Initial fix of upstream merge.

CHANGES

@@ -12,6 +12,96 @@ various other people, all of whom are (hopefully) listed below.
 ------------------------------------------------------------
 
 
+OS/161 2.0.3 released 20160124
+------------------------------
+
+20170124 dholland in base
+   - Remove obsolete, redundant, or not useful test programs:
+	guzzle (same as hog)
+	kitchen (equivalent to multiexec -n 4 sink)
+	sink (same as conman)
+	sty (equivalent to multiexec -n 6 hog)
+	quinthuge (offers little over triplehuge, can be done with multiexec)
+	quintmat, quintsort (ditto)
+
+20170118 dholland in base
+   - Make -g -Og the flags when "debug" is enabled in a kernel config
+     (which it is in the non-OPT ones) and add an additional kernel
+     config verb "debugonly" to get just -g in case that becomes
+     necessary. This should significantly improve the output code
+     quality from gcc without compromising debugging. (However, gcc
+     being gcc, it also sometimes leads to additional spurious
+     warnings that don't occur with either -g or -O2.)
+
+20170118 dholland in base
+   - Add a MI mainbus_debugger() function that goes through the right
+     MD paths to trigger the debugger hook in the ltrace device. Also
+     add a menu function "debug" to trigger it.
+
+20170118 dholland in base
+   - Add some bits to forktest to try to catch the case where the fork
+     child returns from the next system call instead of from fork.
+     (Which is a moderately common bug, caused by races copying the
+     trapframe information in the kernel.)
+
+20170117 dholland in base
+   - Add a menu command "deadlock" to intentionally deadlock.
+
+20170117 dholland in base, from Sam Fishman
+   - Fix parallelvm -w so that if one of the forks fails the whole
+     thing doesn't wedge.
+
+20170117 dholland in base, reported by Sam Fishman
+   - Don't do semfs I/O from NULL, or from/to insufficiently sized
+     buffers. Like the 20150615 change, except covering the rest of
+     the tests that use the semaphores that were doing it wrong:
+     multiexec, parallelvm, and schedpong.
+
+20170117 dholland in base, from Sam Fishman
+   - Add assembler directives to exception-mips1.S that tell gdb how
+     to read trap frames correctly. Garbage-collect old stuff left
+     over from making it work with a (much) older version of gdb a
+     long time back. This also usually makes it possible to trace back
+     through a syscall into a userlevel process; include a gdb script
+     with tools for making this useful.
+
+20170117 dholland in base
+   - Merge the deadlock detector into base. It was a success last year.
+   - Mention in the comments that the hangman hooks in locks need to
+     be called atomically.
+
+20170117 dholland in base, reported by Jeffrey Cai, patch from Sam Fishman
+   - Fix off-by-one in tac that makes it skip the first line of files.
+
+20170117 dholland in base, from Sam Fishman
+   - Make badcall's "pipe with unaligned pointer" test clean up after
+     itself if the operation succeeds. Otherwise it leaks fds and that
+     can intefere with other tests.
+
+20170116 dholland in base, reported by Sam Fishman
+   - Don't allow opening an entirely empty pathname to succeed, and
+     don't allow success for this case in badcall either.
+
+20170116 dholland in base, from Sasha Fedorova
+   - Fix write buffer size in filetest.
+
+20160325 dholland in base
+   - Fix macro parenthesis bug in ROUNDUP().
+
+20160304 dholland in base, from Sam Fishman
+   - Make runtest.py handle spacing in the command strings it's given.
+
+20160216 dholland in base
+   - Fix spacing problems in ls -l output for large files.
+
+20160203 dholland in base
+   - Expand comments attached to cpustacks[]/cputhreads[], prompted by
+     James Mickens.
+
+20160125 dholland in base, from Nikhil Benesch.
+   - Fix stupid argument handling bug in test.py.
+
+
 OS/161 2.0.2 released 20160112
 ------------------------------
 
@@ -53,6 +143,14 @@ OS/161 2.0.2 released 20160112
      anyway. If they aren't actually constant because of bugs, reading
      a stale or even garbage value is not going to hurt more.
 
+20160107 dholland in deadlock-detector
+   - Add a deadlock detector. For now this will be supplied to
+     instructors as a supplementary patch, because it intrudes into
+     the synchronization primitives and affects what students do
+     there. We are planning to try it on our students this coming
+     semester; if that works out well, I'll probably merge it into
+     base.
+
 20160107 dholland in base
    - In testbin/multiexec, if fork fails partway through, continue
      with the forks we got. Otherwise the subprocesses we started hang

kern/arch/mips/include/trapframe.h

@@ -69,8 +69,6 @@ struct trapframe {
 	uint32_t tf_s7;
 	uint32_t tf_t8;
 	uint32_t tf_t9;
-	uint32_t tf_k0;		/* dummy (see exception-mips1.S comments) */
-	uint32_t tf_k1;		/* dummy */
 	uint32_t tf_gp;
 	uint32_t tf_sp;
 	uint32_t tf_s8;

kern/arch/mips/locore/exception-mips1.S

@@ -101,6 +101,8 @@ mips_general_end:
    .text
    .type common_exception,@function
    .ent common_exception
+   .cfi_startproc
+   .cfi_signal_frame
 common_exception:
    mfc0 k0, c0_status		/* Get status register */
    andi k0, k0, CST_KUp		/* Check the we-were-in-user-mode bit */
@@ -130,11 +132,12 @@ common_exception:
     */
 
    /*
-    * Allocate stack space for 37 words to hold the trap frame,
+    * Allocate stack space for 35 words to hold the trap frame,
     * plus four more words for a minimal argument block, plus
     * one more for proper (64-bit) stack alignment.
     */
-   addi sp, sp, -168
+   addi sp, sp, -160
+   .cfi_def_cfa sp, 0
 
    /*
     * Save general registers.
@@ -143,70 +146,89 @@ common_exception:
     *
     * The order here must match mips/include/trapframe.h.
     *
-    * gdb disassembles this code to try to figure out what registers
+    * gdb uses the .cfi_offset assembler directives inserted below to
-    * are where, and it isn't very bright. So in order to make gdb be
+    * to figure out where each register is stored. Since we've marked
-    * able to trace the stack back through here, we play some silly
+    * this function as a "signal handler" with the .cfi_signal_frame
-    * games.
+    * directive, gdb won't complain about the fact that the stack
+    * is noncontiguous (if we're coming from userland).
     *
-    * In particular:
+    * We also play a trick with the return address: we mark the ra
-    *    (1) We store the return address register into the epc slot,
+    * register as stored to the stack normally and then mark the
-    *        which makes gdb think it's the return address slot. Then
+    * return address for *this* function as being in the k1 register
-    *        we store the real epc value over that.
+    * using the .cfi_return_column directive. gdb is then able to
-    *    (2) We store the current sp into the sp slot, which makes gdb
+    * recognize that the ra we've stored here is the return address
-    *        think it's the stack pointer slot. Then we store the real
+    * for the function that was executing when this exception was
-    *        value.
+    * taken.
-    *    (3) gdb also assumes that saved registers in a function are
-    *        saved in order. This is why we put epc where it is, and
-    *        handle the real value of ra afterwards.
-    *    (4) Because gdb will think we're saving k0 and k1, we need to
-    *        leave slots for them in the trap frame, even though the
-    *        stuff we save there is useless.
     *
-    * This logic has not been tested against a recent gdb and has
+    * All of the cfi (call frame information) material is compiled
-    * probably bitrotted. Someone(TM) should figure out what gdb
+    * into the .eh_frame section of the compiled kernel.
-    * currently expects -- or maybe even patch gdb to understand a
-    * better form of this that doesn't waste so many cycles.
     */
-   sw ra, 160(sp)	/* dummy for gdb */
+   sw s8, 148(sp)	/* save s8 */
-   sw s8, 156(sp)	/* save s8 */
+   .cfi_offset s8, 148
-   sw sp, 152(sp)	/* dummy for gdb */
+   sw k1, 144(sp)	/* real saved sp */
-   sw gp, 148(sp)	/* save gp */
+   .cfi_offset sp, 144
-   sw k1, 144(sp)	/* dummy for gdb */
+   sw gp, 140(sp)	/* save gp */
-   sw k0, 140(sp)	/* dummy for gdb */
-
-   sw k1, 152(sp)	/* real saved sp */
    nop			/* delay slot for store */
+   .cfi_offset gp, 140
 
+   .cfi_return_column k1
    mfc0 k1, c0_epc	/* Copr.0 reg 13 == PC for exception */
-   sw k1, 160(sp)	/* real saved PC */
+   sw k1, 152(sp)	/* real saved PC */
+   .cfi_offset k1, 152
 
    sw t9, 136(sp)
+   .cfi_offset t9, 136
    sw t8, 132(sp)
+   .cfi_offset t8, 132
    sw s7, 128(sp)
+   .cfi_offset s7, 128
    sw s6, 124(sp)
+   .cfi_offset s6, 124
    sw s5, 120(sp)
+   .cfi_offset s5, 120
    sw s4, 116(sp)
+   .cfi_offset s4, 116
    sw s3, 112(sp)
+   .cfi_offset s3, 112
    sw s2, 108(sp)
+   .cfi_offset s2, 108
    sw s1, 104(sp)
+   .cfi_offset s1, 104
    sw s0, 100(sp)
+   .cfi_offset s0, 100
    sw t7, 96(sp)
+   .cfi_offset t7, 96
    sw t6, 92(sp)
+   .cfi_offset t6, 92
    sw t5, 88(sp)
+   .cfi_offset t5, 88
    sw t4, 84(sp)
+   .cfi_offset t4, 84
    sw t3, 80(sp)
+   .cfi_offset t3, 80
    sw t2, 76(sp)
+   .cfi_offset t2, 76
    sw t1, 72(sp)
+   .cfi_offset t1, 72
    sw t0, 68(sp)
+   .cfi_offset t0, 68
    sw a3, 64(sp)
+   .cfi_offset a3, 64
    sw a2, 60(sp)
+   .cfi_offset a2, 60
    sw a1, 56(sp)
+   .cfi_offset a1, 56
    sw a0, 52(sp)
+   .cfi_offset a0, 52
    sw v1, 48(sp)
+   .cfi_offset v1, 48
    sw v0, 44(sp)
+   .cfi_offset v0, 44
    sw AT, 40(sp)
+   .cfi_offset AT, 40
 
    sw ra, 36(sp)
+   .cfi_offset ra, 36
 
    /*
     * Save special registers.
@@ -227,11 +249,6 @@ common_exception:
    mfc0 t4, c0_cause
    sw   t4, 24(sp)               /* Copr.0 reg 13 == exception cause */
 
-   /*
-    * Pretend to save $0 for gdb's benefit.
-    */
-   sw $0, 12(sp)
-
    /*
     * Load the curthread register if coming from user mode.
     */
@@ -260,9 +277,6 @@ common_exception:
    jal mips_trap		/* call it */
    nop				/* delay slot */
 
-   /* Something must be here or gdb doesn't find the stack frame. */
-   nop
-
    /*
     * Now restore stuff and return from the exception.
     * Interrupts should be off.
@@ -309,20 +323,17 @@ exception_return:
    lw s7, 128(sp)
    lw t8, 132(sp)
    lw t9, 136(sp)
+   lw gp, 140(sp)		/* restore gp */
+   /*     144(sp)		   stack pointer - below */
+   lw s8, 148(sp)		/* restore s8 */
+   lw k1, 152(sp)		/* fetch exception return PC into k1 */
 
-   /*     140(sp)		   "saved" k0 was dummy garbage anyway */
+   lw sp, 144(sp)		/* fetch saved sp (must be last) */
-   /*     144(sp)		   "saved" k1 was dummy garbage anyway */
-
-   lw gp, 148(sp)		/* restore gp */
-   /*     152(sp)		   stack pointer - below */
-   lw s8, 156(sp)		/* restore s8 */
-   lw k0, 160(sp)		/* fetch exception return PC into k0 */
-
-   lw sp, 152(sp)		/* fetch saved sp (must be last) */
 
    /* done */
-   jr k0			/* jump back */
+   jr k1			/* jump back */
    rfe				/* in delay slot */
+   .cfi_endproc
    .end common_exception
 
 /*

kern/arch/mips/locore/trap.c

@@ -130,8 +130,8 @@ mips_trap(struct trapframe *tf)
 	bool iskern;
 	int spl;
 
-	/* The trap frame is supposed to be 37 registers long. */
+	/* The trap frame is supposed to be 35 registers long. */
-	KASSERT(sizeof(struct trapframe)==(37*4));
+	KASSERT(sizeof(struct trapframe)==(35*4));
 
 	/*
 	 * Extract the exception code info from the register fields.

kern/arch/mips/thread/cpu.c

@@ -54,6 +54,14 @@
  *
  * These arrays are also used to start up new CPUs, for roughly the
  * same reasons.
+ *
+ * The values in the current cpu's slots in these arrays are updated
+ * with the current thread's information in trap.c before heading to
+ * userlevel, as well as being initialized in cpu_machdep_init below.
+ * This means that (unless something really horrible happens) on entry
+ * to the kernel, and when a new CPU starts up in cpu_start_secondary,
+ * they will have the information needed to figure out who we are and
+ * proceed.
  */
 
 vaddr_t cpustacks[MAXCPUS];

kern/arch/sys161/dev/lamebus_machdep.c

@@ -42,6 +42,7 @@
 #include <mainbus.h>
 #include <sys161/bus.h>
 #include <lamebus/lamebus.h>
+#include <lamebus/ltrace.h>
 #include "autoconf.h"
 
 /*
@@ -275,6 +276,15 @@ mainbus_send_ipi(struct cpu *target)
 	lamebus_assert_ipi(lamebus, target);
 }
 
+/*
+ * Trigger the debugger.
+ */
+void
+mainbus_debugger(void)
+{
+	ltrace_stop(0);
+}
+
 /*
  * Interrupt dispatcher.
  */

kern/conf/DUMBVM

@@ -3,7 +3,9 @@
 
 include conf/conf.kern		# get definitions of available options
 
-debug				# Compile with debug info.
+debug				# Compile with debug info and -Og.
+#debugonly			# Compile with debug info only (no -Og).
+options hangman 		# Deadlock detection. (off by default)
 
 #
 # Device drivers for hardware.

kern/conf/DUMBVM-OPT

@@ -7,6 +7,7 @@
 include conf/conf.kern		# get definitions of available options
 
 #debug				# Optimizing compile (no debug).
+#debugonly
 options noasserts		# Disable assertions.
 
 #

kern/conf/GENERIC

@@ -5,6 +5,8 @@
 include conf/conf.kern		# get definitions of available options
 
 debug				# Compile with debug info.
+#debugonly			# Compile with debug info only (no -Og).
+#options hangman 		# Deadlock detection. (off by default)
 
 #
 # Device drivers for hardware.

kern/conf/GENERIC-OPT

@@ -7,6 +7,7 @@
 include conf/conf.kern		# get definitions of available options
 
 #debug				# Optimizing compile (no debug).
+#debugonly
 options noasserts		# Disable assertions.
 
 #

kern/conf/conf.kern

@@ -334,6 +334,9 @@ file      thread/synch.c
 file      thread/thread.c
 file      thread/threadlist.c
 
+defoption hangman
+optfile   hangman thread/hangman.c
+
 #
 # Process system
 #

kern/conf/config

@@ -12,7 +12,8 @@
 # Recognized directives:
 #
 #    file <filename>          use source file
-#    debug                    turn on debug info
+#    debug                    turn on debug info and -Og
+#    debugonly                turn on debug info without -Og
 #    defoption <sym>          define an option
 #    optfile <sym> <file>     if option <sym> is enabled, use file <file>
 #    optofffile <sym> <file>  if option <sym> is disabled, use file <file>
@@ -97,6 +98,7 @@ echo "$CONFNAME" $CONFTMP | awk '
 	nfields["include"] = 2;
 	nfields["file"] = 2;
 	nfields["debug"] = 1;
+	nfields["debugonly"] = 1;
 	nfields["defoption"] = 2;
 	nfields["optfile"] = 3;
 	nfields["optofffile"] = 3;
@@ -776,6 +778,9 @@ echo -n ' files.mk'
 	# Default: optimize.
 	BEGIN { debugflags="-O2"; }
 	$1=="debug" {
+	    debugflags="-g -Og";
+	}
+	$1=="debugonly" {
 	    debugflags="-g";
 	}
 

kern/gdbscripts/mips-userland

@@ -0,0 +1,40 @@
+# commands to interact with userland
+
+define load-userprogram
+    init-if-undefined $userprog_loaded = 0
+    if !$userprog_loaded || !$_streq($arg0, $cur_userprog)
+        add-symbol-file $arg0 0x4000b0
+        # remove after adding the new file in case add-symbol-file fails
+        if $userprog_loaded
+            remove-symbol-file -a 0x4000b0
+        end
+        set $userprog_loaded = 1
+        set $cur_userprog = $arg0
+    end
+end
+document load-userprogram
+Loads a single user program into gdb's symbol table, removing
+the previous user program loaded if one exists.
+Usage: load-userprogram <path-to-prog>
+end
+alias -a lu = load-userprogram
+
+define auto-userprogram
+    set $pname = curthread->t_proc->p_name
+    if $pname != 0 && $pname[0] != 0 && !$_streq($pname, "[kernel]")
+        if $pname[0] == '/'
+            set $pname = $pname + 1
+        end
+        # This dumbness works around the fact that gdb doesn't
+        # expand convenience variables when you execute commands.
+        # And setting the third parameter to True silences the command.
+        python gdb.execute("load-userprogram " + str(gdb.parse_and_eval("$pname")).split()[1], False, True)
+    end
+end
+document auto-userprogram
+Calls load-userprogram on whatever is curproc->p_name. It is meant
+to work with kernels that set p_name to an absolute path to the
+program, and it is designed to be called from hook-stop.
+Usage: auto-userprogram
+end
+

kern/include/cpu.h

@@ -88,6 +88,11 @@ struct cpu {
 	struct tlbshootdown c_shootdown[TLBSHOOTDOWN_MAX];
 	unsigned c_numshootdown;
 	struct spinlock c_ipi_lock;
+
+	/*
+	 * Accessed by other cpus. Protected inside hangman.c.
+	 */
+	HANGMAN_ACTOR(c_hangman);
 };
 
 /*

kern/include/hangman.h

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2015
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef HANGMAN_H
+#define HANGMAN_H
+
+/*
+ * Simple deadlock detector. Enable with "options hangman" in the
+ * kernel config.
+ */
+
+#include "opt-hangman.h"
+
+#if OPT_HANGMAN
+
+struct hangman_actor {
+	const char *a_name;
+	const struct hangman_lockable *a_waiting;
+};
+
+struct hangman_lockable {
+	const char *l_name;
+	const struct hangman_actor *l_holding;
+};
+
+void hangman_wait(struct hangman_actor *a, struct hangman_lockable *l);
+void hangman_acquire(struct hangman_actor *a, struct hangman_lockable *l);
+void hangman_release(struct hangman_actor *a, struct hangman_lockable *l);
+
+#define HANGMAN_ACTOR(sym)	struct hangman_actor sym
+#define HANGMAN_LOCKABLE(sym)	struct hangman_lockable sym
+
+#define HANGMAN_ACTORINIT(a, n)	    ((a)->a_name = (n), (a)->a_waiting = NULL)
+#define HANGMAN_LOCKABLEINIT(l, n)  ((l)->l_name = (n), (l)->l_holding = NULL)
+
+#define HANGMAN_LOCKABLE_INITIALIZER	{ "spinlock", NULL }
+
+#define HANGMAN_WAIT(a, l)	hangman_wait(a, l)
+#define HANGMAN_ACQUIRE(a, l)	hangman_acquire(a, l)
+#define HANGMAN_RELEASE(a, l)	hangman_release(a, l)
+
+#else
+
+#define HANGMAN_ACTOR(sym)
+#define HANGMAN_LOCKABLE(sym)
+
+#define HANGMAN_ACTORINIT(a, name)
+#define HANGMAN_LOCKABLEINIT(a, name)
+
+#define HANGMAN_LOCKABLE_INITIALIZER
+
+#define HANGMAN_WAIT(a, l)
+#define HANGMAN_ACQUIRE(a, l)
+#define HANGMAN_RELEASE(a, l)
+
+#endif
+
+#endif /* HANGMAN_H */

kern/include/lib.h

@@ -194,7 +194,7 @@ void kprintf_bootstrap(void);
  */
 
 #define DIVROUNDUP(a,b) (((a)+(b)-1)/(b))
-#define ROUNDUP(a,b)    (DIVROUNDUP(a,b)*b)
+#define ROUNDUP(a,b)    (DIVROUNDUP(a,b)*(b))
 
 
 #endif /* _LIB_H_ */

kern/include/mainbus.h

@@ -55,6 +55,9 @@ size_t mainbus_ramsize(void);
 /* Switch on an inter-processor interrupt. (Low-level.) */
 void mainbus_send_ipi(struct cpu *target);
 
+/* Request breaking into the debugger, where available. */
+void mainbus_debugger(void);
+
 /*
  * The various ways to shut down the system. (These are very low-level
  * and should generally not be called directly - md_poweroff, for

kern/include/spinlock.h

@@ -36,6 +36,7 @@
  */
 
 #include <cdefs.h>
+#include <hangman.h>
 
 /* Inlining support - for making sure an out-of-line copy gets built */
 #ifndef SPINLOCK_INLINE
@@ -57,12 +58,18 @@
 struct spinlock {
 	volatile spinlock_data_t splk_lock; /* Memory word where we spin. */
 	struct cpu *splk_holder;	    /* CPU holding this lock. */
+	HANGMAN_LOCKABLE(splk_hangman);     /* Deadlock detector hook. */
 };
 
 /*
  * Initializer for cases where a spinlock needs to be static or global.
  */
+#ifdef OPT_HANGMAN
+#define SPINLOCK_INITIALIZER	{ SPINLOCK_DATA_INITIALIZER, NULL, \
+				  HANGMAN_LOCKABLE_INITIALIZER }
+#else
 #define SPINLOCK_INITIALIZER	{ SPINLOCK_DATA_INITIALIZER, NULL }
+#endif
 
 /*
  * Spinlock functions.

kern/include/synch.h

@@ -74,6 +74,7 @@ void V(struct semaphore *);
  */
 struct lock {
         char *lk_name;
+        HANGMAN_LOCKABLE(lk_hangman);   /* Deadlock detector hook. */
         // add what you need here
         // (don't forget to mark things volatile as needed)
 };

kern/include/thread.h

@@ -93,6 +93,7 @@ struct thread {
 	struct switchframe *t_context;	/* Saved register context (on stack) */
 	struct cpu *t_cpu;		/* CPU thread runs on */
 	struct proc *t_proc;		/* Process thread belongs to */
+	HANGMAN_ACTOR(t_hangman);	/* Deadlock detector hook */
 
 	/*
 	 * Interrupt state fields.

kern/include/version.h

@@ -34,7 +34,7 @@
  * Leave this alone, so we can tell what version of the OS/161 base
  * code we gave you.
  */
-#define BASE_VERSION    "2.0.2"
+#define BASE_VERSION    "2.0.3"
 
 /*
  * Change this as you see fit in the course of hacking the system.

kern/main/menu.c

@@ -35,6 +35,8 @@
 #include <lib.h>
 #include <uio.h>
 #include <clock.h>
+#include <mainbus.h>
+#include <synch.h>
 #include <thread.h>
 #include <proc.h>
 #include <vfs.h>
@@ -247,6 +249,21 @@ cmd_sync(int nargs, char **args)
 	return 0;
 }
 
+/*
+ * Command for dropping to the debugger.
+ */
+static
+int
+cmd_debug(int nargs, char **args)
+{
+	(void)nargs;
+	(void)args;
+
+	mainbus_debugger();
+
+	return 0;
+}
+
 /*
  * Command for doing an intentional panic.
  */
@@ -261,6 +278,81 @@ cmd_panic(int nargs, char **args)
 	return 0;
 }
 
+/*
+ * Subthread for intentially deadlocking.
+ */
+struct deadlock {
+	struct lock *lock1;
+	struct lock *lock2;
+};
+
+static
+void
+cmd_deadlockthread(void *ptr, unsigned long num)
+{
+	struct deadlock *dl = ptr;
+
+	(void)num;
+
+	/* If it doesn't wedge right away, keep trying... */
+	while (1) {
+		lock_acquire(dl->lock2);
+		lock_acquire(dl->lock1);
+		kprintf("+");
+		lock_release(dl->lock1);
+		lock_release(dl->lock2);
+	}
+}
+
+/*
+ * Command for doing an intentional deadlock.
+ */
+static
+int
+cmd_deadlock(int nargs, char **args)
+{
+	struct deadlock dl;
+	int result;
+
+	(void)nargs;
+	(void)args;
+
+	dl.lock1 = lock_create("deadlock1");
+	if (dl.lock1 == NULL) {
+		kprintf("lock_create failed\n");
+		return ENOMEM;
+	}
+	dl.lock2 = lock_create("deadlock2");
+	if (dl.lock2 == NULL) {
+		lock_destroy(dl.lock1);
+		kprintf("lock_create failed\n");
+		return ENOMEM;
+	}
+
+	result = thread_fork(args[0] /* thread name */,
+			NULL /* kernel thread */,
+			cmd_deadlockthread /* thread function */,
+			&dl /* thread arg */, 0 /* thread arg */);
+	if (result) {
+		kprintf("thread_fork failed: %s\n", strerror(result));
+		lock_release(dl.lock1);
+		lock_destroy(dl.lock2);
+		lock_destroy(dl.lock1);
+		return result;
+	}
+
+	/* If it doesn't wedge right away, keep trying... */
+	while (1) {
+		lock_acquire(dl.lock1);
+		lock_acquire(dl.lock2);
+		kprintf(".");
+		lock_release(dl.lock2);
+		lock_release(dl.lock1);
+	}
+	/* NOTREACHED */
+	return 0;
+}
+
 /*
  * Command for shutting down.
  */
@@ -463,7 +555,9 @@ static const char *opsmenu[] = {
 	"[cd]      Change directory          ",
 	"[pwd]     Print current directory   ",
 	"[sync]    Sync filesystems          ",
+	"[debug]   Drop to debugger          ",
 	"[panic]   Intentional panic         ",
+	"[deadlock] Intentional deadlock     ",
 	"[q]       Quit and shut down        ",
 	NULL
 };
@@ -614,7 +708,9 @@ static struct {
 	{ "cd",		cmd_chdir },
 	{ "pwd",	cmd_pwd },
 	{ "sync",	cmd_sync },
+	{ "debug",	cmd_debug },
 	{ "panic",	cmd_panic },
+	{ "deadlock",	cmd_deadlock },
 	{ "q",		cmd_quit },
 	{ "exit",	cmd_quit },
 	{ "halt",	cmd_quit },

kern/test/arraytest.c

@@ -156,6 +156,9 @@ arraytest2(int nargs, char **args)
 	(void)nargs;
 	(void)args;
 
+	/* Silence warning with gcc 4.8 -Og (but not -O2) */
+	x = 0;
+
 	kprintf("Beginning large array test...\n");
 	a = array_create();
 	KASSERT(a != NULL);

kern/test/fstest.c

@@ -681,7 +681,7 @@ checkfilesystem(int nargs, char **args)
 	char *device;
 
 	if (nargs != 2) {
-		kprintf("Usage: fs[12345] filesystem:\n");
+		kprintf("Usage: fs[123456] filesystem:\n");
 		return EINVAL;
 	}
 

kern/thread/hangman.c

@@ -0,0 +1,182 @@
+/*
+ * Copyright (c) 2015
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * Simple deadlock detector.
+ */
+
+#include <types.h>
+#include <lib.h>
+#include <spl.h>
+#include <spinlock.h>
+#include <hangman.h>
+
+static struct spinlock hangman_lock = SPINLOCK_INITIALIZER;
+
+/*
+ * Look for a path through the waits-for graph that goes from START to
+ * TARGET.
+ *
+ * Because lockables can only be held by one actor, and actors can
+ * only be waiting for one thing at a time, this turns out to be
+ * quite simple.
+ */
+static
+void
+hangman_check(const struct hangman_lockable *start,
+	      const struct hangman_actor *target)
+{
+	const struct hangman_actor *cur;
+
+	cur = start->l_holding;
+	while (cur != NULL) {
+		if (cur == target) {
+			goto found;
+		}
+		if (cur->a_waiting == NULL) {
+			break;
+		}
+		cur = cur->a_waiting->l_holding;
+	}
+	return;
+
+ found:
+	/*
+	 * None of this can change while we print it (that's the point
+	 * of it being a deadlock) so drop hangman_lock while
+	 * printing; otherwise we can come back via kprintf_spinlock
+	 * and that makes a mess. But force splhigh() explicitly so
+	 * the console prints in polled mode and to discourage other
+	 * things from running in the middle of the printout.
+	 */
+	splhigh();
+	spinlock_release(&hangman_lock);
+
+	kprintf("hangman: Detected lock cycle!\n");
+	kprintf("hangman: in %s (%p);\n", target->a_name, target);
+	kprintf("hangman: waiting for %s (%p), but:\n", start->l_name, start);
+	kprintf("   lockable %s (%p)\n", start->l_name, start);
+	cur = start->l_holding;
+	while (cur != target) {
+		kprintf("   held by actor %s (%p)\n", cur->a_name, cur);
+		kprintf("   waiting for lockable %s (%p)\n",
+			cur->a_waiting->l_name, cur->a_waiting);
+		cur = cur->a_waiting->l_holding;
+	}
+	kprintf("   held by actor %s (%p)\n", cur->a_name, cur);
+	panic("Deadlock.\n");
+}
+
+/*
+ * Note that a is about to wait for l.
+ *
+ * Note that there's no point calling this if a isn't going to wait,
+ * because in that case l->l_holding will be null and the check
+ * won't go anywhere.
+ *
+ * One could also maintain in memory a graph of all requests ever
+ * seen, in order to detect lock order inversions that haven't
+ * actually deadlocked; but there are a lot of ways in which this is
+ * tricky and problematic. For now we'll settle for just detecting and
+ * reporting deadlocks that do happen.
+ */
+void
+hangman_wait(struct hangman_actor *a,
+	     struct hangman_lockable *l)
+{
+	if (l == &hangman_lock.splk_hangman) {
+		/* don't recurse */
+		return;
+	}
+
+	spinlock_acquire(&hangman_lock);
+
+	if (a->a_waiting != NULL) {
+		spinlock_release(&hangman_lock);
+		panic("hangman_wait: already waiting for something?\n");
+	}
+
+	hangman_check(l, a);
+	a->a_waiting = l;
+
+	spinlock_release(&hangman_lock);
+}
+
+void
+hangman_acquire(struct hangman_actor *a,
+		struct hangman_lockable *l)
+{
+	if (l == &hangman_lock.splk_hangman) {
+		/* don't recurse */
+		return;
+	}
+
+	spinlock_acquire(&hangman_lock);
+
+	if (a->a_waiting != l) {
+		spinlock_release(&hangman_lock);
+		panic("hangman_acquire: not waiting for lock %s (%p)\n",
+		      l->l_name, l);
+	}
+	if (l->l_holding != NULL) {
+		spinlock_release(&hangman_lock);
+		panic("hangman_acquire: lock %s (%p) still held by %s (%p)\n",
+		      l->l_name, l, a->a_name, a);
+	}
+
+	l->l_holding = a;
+	a->a_waiting = NULL;
+
+	spinlock_release(&hangman_lock);
+}
+
+void
+hangman_release(struct hangman_actor *a,
+		struct hangman_lockable *l)
+{
+	if (l == &hangman_lock.splk_hangman) {
+		/* don't recurse */
+		return;
+	}
+
+	spinlock_acquire(&hangman_lock);
+
+	if (a->a_waiting != NULL) {
+		spinlock_release(&hangman_lock);
+		panic("hangman_release: waiting for something?\n");
+	}
+	if (l->l_holding != a) {
+		spinlock_release(&hangman_lock);
+		panic("hangman_release: not the holder\n");
+	}
+
+	l->l_holding = NULL;
+
+	spinlock_release(&hangman_lock);
+}

kern/thread/spinlock.c

@@ -52,6 +52,7 @@ spinlock_init(struct spinlock *splk)
 {
 	spinlock_data_set(&splk->splk_lock, 0);
 	splk->splk_holder = NULL;
+	HANGMAN_LOCKABLEINIT(&splk->splk_hangman, "spinlock");
 }
 
 /*
@@ -85,6 +86,8 @@ spinlock_acquire(struct spinlock *splk)
 			panic("Deadlock on spinlock %p\n", splk);
 		}
 		mycpu->c_spinlocks++;
+
+		HANGMAN_WAIT(&curcpu->c_hangman, &splk->splk_hangman);
 	}
 	else {
 		mycpu = NULL;
@@ -112,6 +115,10 @@ spinlock_acquire(struct spinlock *splk)
 
 	membar_store_any();
 	splk->splk_holder = mycpu;
+
+	if (CURCPU_EXISTS()) {
+		HANGMAN_ACQUIRE(&curcpu->c_hangman, &splk->splk_hangman);
+	}
 }
 
 /*
@@ -125,6 +132,7 @@ spinlock_release(struct spinlock *splk)
 		KASSERT(splk->splk_holder == curcpu->c_self);
 		KASSERT(curcpu->c_spinlocks > 0);
 		curcpu->c_spinlocks--;
+		HANGMAN_RELEASE(&curcpu->c_hangman, &splk->splk_hangman);
 	}
 
 	splk->splk_holder = NULL;

kern/thread/synch.c

@@ -154,6 +154,8 @@ lock_create(const char *name)
 		return NULL;
 	}
 
+	HANGMAN_LOCKABLEINIT(&lock->lk_hangman, lock->lk_name);
+
 	// add stuff here as needed
 
 	return lock;
@@ -173,14 +175,23 @@ lock_destroy(struct lock *lock)
 void
 lock_acquire(struct lock *lock)
 {
+	/* Call this (atomically) before waiting for a lock */
+	//HANGMAN_WAIT(&curthread->t_hangman, &lock->lk_hangman);
+
 	// Write this
 
 	(void)lock;  // suppress warning until code gets written
+
+	/* Call this (atomically) once the lock is acquired */
+	//HANGMAN_ACQUIRE(&curthread->t_hangman, &lock->lk_hangman);
 }
 
 void
 lock_release(struct lock *lock)
 {
+	/* Call this (atomically) when the lock is released */
+	//HANGMAN_RELEASE(&curthread->t_hangman, &lock->lk_hangman);
+
 	// Write this
 
 	(void)lock;  // suppress warning until code gets written

kern/thread/thread.c

@@ -145,6 +145,7 @@ thread_create(const char *name)
 	thread->t_context = NULL;
 	thread->t_cpu = NULL;
 	thread->t_proc = NULL;
+	HANGMAN_ACTORINIT(&thread->t_hangman, thread->t_name);
 
 	/* Interrupt state fields */
 	thread->t_in_interrupt = false;
@@ -244,6 +245,8 @@ cpu_create(unsigned hardware_number)
 		curcpu->c_curthread = curthread;
 	}
 
+	HANGMAN_ACTORINIT(&c->c_hangman, "cpu");
+
 	result = proc_addthread(kproc, c->c_curthread);
 	if (result) {
 		panic("cpu_create: proc_addthread:: %s\n", strerror(result));

kern/vfs/vfslist.c

@@ -129,6 +129,23 @@ vfs_biglock_acquire(void)
 	if (!lock_do_i_hold(vfs_biglock)) {
 		lock_acquire(vfs_biglock);
 	}
+	else if (vfs_biglock_depth == 0) {
+		/*
+		 * Supposedly we hold it, but the depth is 0. This may
+		 * mean: (1) the count is messed up, or (2)
+		 * lock_do_i_hold is lying. Since OS/161 ships out of
+		 * the box with unimplemented locks (students
+		 * implement them) that always return true, assume
+		 * situation (2). In this case acquire the lock
+		 * anyway.
+		 *
+		 * Once you have working locks, this won't be the
+		 * case, and if you get here it should be situation
+		 * (1), in which case the count is messed up and one
+		 * can panic.
+		 */
+		lock_acquire(vfs_biglock);
+	}
 	vfs_biglock_depth++;
 }
 
@@ -381,6 +398,9 @@ vfs_doadd(const char *dname, int mountable, struct device *dev, struct fs *fs)
 	unsigned index;
 	int result;
 
+	/* Silence warning with gcc 4.8 -Og (but not -O2) */
+	index = 0;
+
 	vfs_biglock_acquire();
 
 	name = kstrdup(dname);

kern/vfs/vfslookup.c

@@ -135,6 +135,13 @@ getdevice(char *path, char **subpath, struct vnode **startvn)
 
 	KASSERT(vfs_biglock_do_i_hold());
 
+	/*
+	 * Entirely empty filenames aren't legal.
+	 */
+	if (path[0] == 0) {
+		return EINVAL;
+	}
+
 	/*
 	 * Locate the first colon or slash.
 	 */

kern/vm/kmalloc.c

@@ -1113,6 +1113,10 @@ subpage_kfree(void *ptr)
 
 	checksubpages();
 
+	/* Silence warnings with gcc 4.8 -Og (but not -O2) */
+	prpage = 0;
+	blktype = 0;
+
 	for (pr = allbase; pr; pr = pr->next_all) {
 		prpage = PR_PAGEADDR(pr);
 		blktype = PR_BLOCKTYPE(pr);

mk/os161.mkdirs.mk

@@ -1,5 +1,5 @@
 #
-# MKDIRS logic
+# OS/161 build environment: MKDIRS logic
 #
 # This generates rules for all intermediate directories as well as
 # the directories listed. (That is, if you say MKDIRS=/usr/bin/foo

mk/os161.script.mk

@@ -0,0 +1,92 @@
+#
+# OS/161 build environment: install scripts
+#
+# Usage:
+#    TOP=../..
+#    .include "$(TOP)/mk/os161.config.mk"
+#    [defs go here]
+#    .include "$(TOP)/mk/os161.man.mk"
+#    [any extra rules go here]
+#
+# Variables controlling this file:
+#
+# EXECSCRIPTS			Executable files to install.
+# NONEXECSCRIPTS		Non-executable files to install.
+#
+# SCRIPTDIR			Directory under $(OSTREE) to install into,
+#                               e.g. /hostbin. Should have a leading slash.
+#
+
+ALLSCRIPTS=$(NONEXECSCRIPTS)
+
+# We may want these directories created. (Used by os161.baserules.mk.)
+MKDIRS+=$(MYBUILDDIR)
+MKDIRS+=$(INSTALLTOP)$(SCRIPTDIR)
+MKDIRS+=$(OSTREE)$(SCRIPTDIR)
+
+# Default rule: "build" the executable scripts. This sets the hash-bang
+# header with the interpreter path.
+# (In make the first rule found is the default.)
+all: all-local
+all-local: $(MYBUILDDIR) .WAIT
+.for S in $(EXECSCRIPTS)
+ALLSCRIPTS+=$(MYBUILDDIR)/$(S)
+all-local: $(MYBUILDDIR)/$(S)
+$(MYBUILDDIR)/$(S): $(S)
+# This must test $@, or assign another variable; it can't test $(S).
+# (This is a bmake bug.)
+.if !empty(@:M*.py)
+	echo '#!'"$(PYTHON_INTERPRETER)" > $@.new
+.else
+	sed -n -e '1p' < $(S) > $@.new
+.endif
+	sed -e '1d' < $(S) >> $@.new
+	chmod 755 $@.new
+	mv -f $@.new $@
+.endfor
+
+# depend doesn't need to do anything
+depend-local: ;
+
+#
+# Install: we can install into either $(INSTALLTOP) or $(OSTREE).
+# When building the whole system, we always install into the staging
+# area. However, if you're working on a particular program it is
+# usually convenient to be able to install it directly to $(OSTREE)
+# instead of doing a complete top-level install.
+#
+# Note that we make a hard link instead of a copy by default to reduce
+# overhead.
+#
+install-staging-local: $(INSTALLTOP)$(SCRIPTDIR) .WAIT
+
+.for _F_ in $(ALLSCRIPTS)
+install-staging-local: $(INSTALLTOP)$(SCRIPTDIR)/$(_F_:T)
+$(INSTALLTOP)$(SCRIPTDIR)/$(_F_:T): $(_F_)
+	rm -f $(.TARGET)
+	ln $(_F_) $(.TARGET) || cp $(_F_) $(.TARGET)
+.endfor
+
+install-local: $(OSTREE)$(SCRIPTDIR) .WAIT installscripts
+installscripts:
+.for _F_ in $(ALLSCRIPTS)
+	rm -f $(OSTREE)$(SCRIPTDIR)/$(_F_:T)
+	ln $(_F_) $(OSTREE)$(SCRIPTDIR)/$(_F_:T) || \
+	  cp $(_F_) $(OSTREE)$(SCRIPTDIR)/$(_F_:T)
+.endfor
+
+# clean: remove build products
+clean-local:
+.for S in $(EXECSCRIPTS)
+	rm -f $(MYBUILDDIR)/$(S)
+.endfor
+
+# Mark targets that don't represent files PHONY, to prevent various
+# lossage if files by those names appear.
+.PHONY: all all-local install-staging-local install-local installscripts
+.PHONY: clean-local
+
+# Finally, get the shared definitions for the most basic rules.
+.include "$(TOP)/mk/os161.baserules.mk"
+
+# End.

userland/bin/ls/ls.c

@@ -177,7 +177,7 @@ print(const char *path)
 			typech = '?';
 		}
 
-		printf("%crwx------ %2d root  %-8llu",
+		printf("%crwx------ %2d root  %-7llu ",
 		       typech,
 		       statbuf.st_nlink,
 		       statbuf.st_size);

userland/bin/tac/tac.c

@@ -197,11 +197,9 @@ dumpdata(void)
 
 	indexsize = dolseek(indexfd, indexname, 0, SEEK_CUR);
 	pos = indexsize;
-	while (1) {
+	assert(pos % sizeof(x) == 0);
+	while (pos > 0) {
 		pos -= sizeof(x);
-		if (pos == 0) {
-			break;
-		}
 		assert(pos >= 0);
 		dolseek(indexfd, indexname, pos, SEEK_SET);
 

userland/testbin/badcall/bad_pipe.c

@@ -69,6 +69,11 @@ pipe_unaligned(void)
 
 	rv = pipe((int *)ptr);
 	report_survival(rv, errno, &result);
+	if (rv == 0) {
+		memmove(fds, ptr, 2*sizeof(int));
+		close(fds[0]);
+		close(fds[1]);
+	}
 	return result;
 }
 

userland/testbin/filetest/filetest.c

@@ -46,7 +46,7 @@
 int
 main(int argc, char *argv[])
 {
-	static char writebuf[40] = "Twiddle dee dee, Twiddle dum dum.......\n";
+	static char writebuf[41] = "Twiddle dee dee, Twiddle dum dum.......\n";
 	static char readbuf[41];
 
 	const char *file;

userland/testbin/forktest/forktest.c

@@ -152,12 +152,20 @@ void
 test(int nowait)
 {
 	int pid0, pid1, pid2, pid3;
+	int depth = 0;
 
 	/*
 	 * Caution: This generates processes geometrically.
 	 *
 	 * It is unrolled to encourage gcc to registerize the pids,
 	 * to prevent wait/exit problems if fork corrupts memory.
+	 *
+	 * Note: if the depth prints trigger and show that the depth
+	 * is too small, the most likely explanation is that the fork
+	 * child is returning from the write() inside putchar()
+	 * instead of from fork() and thus skipping the depth++. This
+	 * is a fairly common problem caused by races in the kernel
+	 * fork code.
 	 */
 
 	/*
@@ -184,18 +192,37 @@ test(int nowait)
 	pid0 = dofork();
 	nprintf(".");
 	write(fd, "A", 1);
+	depth++;
+	if (depth != 1) {
+		warnx("depth %d, should be 1", depth);
+	}
 	check();
+
 	pid1 = dofork();
 	nprintf(".");
 	write(fd, "B", 1);
+	depth++;
+	if (depth != 2) {
+		warnx("depth %d, should be 2", depth);
+	}
 	check();
+
 	pid2 = dofork();
 	nprintf(".");
 	write(fd, "C", 1);
+	depth++;
+	if (depth != 3) {
+		warnx("depth %d, should be 3", depth);
+	}
 	check();
+
 	pid3 = dofork();
 	nprintf(".");
 	write(fd, "D", 1);
+	depth++;
+	if (depth != 4) {
+		warnx("depth %d, should be 4", depth);
+	}
 	check();
 
 	/*

userland/testbin/hog/hog.c

@@ -31,7 +31,7 @@
  * hog.c
  * 	Spawned by several other user programs to test time-slicing.
  *
- * This does not differ from guzzle in any important way.
+ * Loops consuming CPU cycles.
  */
 
 int

userland/testbin/multiexec/multiexec.c

@@ -134,6 +134,7 @@ semP(struct usem *sem, size_t num)
 	if (read(sem->fd, c, num) < 0) {
 		err(1, "%s: read", sem->name);
 	}
+	(void)c;
 }
 
 static

userland/testbin/parallelvm/parallelvm.c

@@ -273,16 +273,24 @@ static
 void
 semP(struct usem *sem, size_t num)
 {
-	if (read(sem->fd, NULL, num) < 0) {
+	char c[num];
+
+	if (read(sem->fd, c, num) < 0) {
 		err(1, "%s: read", sem->name);
 	}
+	(void)c;
 }
 
 static
 void
 semV(struct usem *sem, size_t num)
 {
-	if (write(sem->fd, NULL, num) < 0) {
+	char c[num];
+
+	/* semfs does not use these values, but be conservative */
+	memset(c, 0, num);
+
+	if (write(sem->fd, c, num) < 0) {
 		err(1, "%s: write", sem->name);
 	}
 }
@@ -326,7 +334,12 @@ makeprocs(bool dowait)
 	for (i=0; i<NJOBS; i++) {
 		pids[i] = fork();
 		if (pids[i]<0) {
-			warn("fork");
+			warn("fork (process %d)", i);
+			if (dowait) {
+				semopen(&s1);
+				semV(&s1, 1);
+				semclose(&s1);
+			}
 		}
 		if (pids[i]==0) {
 			/* child */

userland/testbin/schedpong/usem.c

@@ -35,6 +35,7 @@
 
 #include <stdio.h>
 #include <stdarg.h>
+#include <string.h>
 #include <unistd.h>
 #include <err.h>
 
@@ -84,9 +85,9 @@ void
 Pn(struct usem *sem, unsigned count)
 {
 	ssize_t r;
-	char c;
+	char c[count];
 
-	r = read(sem->fd, &c, count);
+	r = read(sem->fd, c, count);
 	if (r < 0) {
 		err(1, "%s: read", sem->name);
 	}
@@ -105,9 +106,12 @@ void
 Vn(struct usem *sem, unsigned count)
 {
 	ssize_t r;
-	char c;
+	char c[count];
 
-	r = write(sem->fd, &c, count);
+	/* semfs does not use these values, but be conservative */
+	memset(c, 0, count);
+
+	r = write(sem->fd, c, count);
 	if (r < 0) {
 		err(1, "%s: write", sem->name);
 	}