Improve crash signal reporting on Windows

This change fixes a bug where exiting a crash signal handler on Windows
after adding the signal to uc_sigmask, but not correcting the CPU state
would cause the signal handler to loop infinitely, causing process hang

Another issue is that very tiny programs, that don't link posix signals
would not have their SIGILL / SIGSEGV / etc. status reported to Cosmo's
bash shell when terminating on crash. That's fixed by a tiny handler in
WinMain() that knows how to map WIN32 crash codes to the POSIX flavors.

Author: jart

build/config.mk

@@ -11,20 +11,20 @@
 #
 ifeq ($(MODE),)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CCFLAGS += -O2 $(BACKTRACES)
 CONFIG_CPPFLAGS += -DSYSDEBUG
 TARGET_ARCH ?= -msse3
 endif
 ifeq ($(MODE), x86_64)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CCFLAGS += -O2 $(BACKTRACES)
 CONFIG_CPPFLAGS += -DSYSDEBUG
 endif
 ifeq ($(MODE), aarch64)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CCFLAGS += -O2 $(BACKTRACES)
 CONFIG_CPPFLAGS += -DSYSDEBUG
 endif
@@ -38,13 +38,13 @@ endif
 #
 ifeq ($(MODE), zero)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 OVERRIDE_CFLAGS += -O0
 OVERRIDE_CXXFLAGS += -O0
 CONFIG_CPPFLAGS += -DSYSDEBUG
 endif
 ifeq ($(MODE), aarch64-zero)
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 OVERRIDE_CFLAGS += -O0 -fdce
 OVERRIDE_CXXFLAGS += -O0 -fdce
 CONFIG_CPPFLAGS += -DSYSDEBUG
@@ -81,7 +81,7 @@ endif
 #
 ifeq ($(MODE), opt)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CPPFLAGS += -DNDEBUG -DSYSDEBUG
 CONFIG_CCFLAGS += $(BACKTRACES) -O3 -fmerge-all-constants
 TARGET_ARCH ?= -march=native
@@ -98,7 +98,7 @@ endif
 #   - Turns off support for other operating systems
 #
 ifeq ($(MODE), optlinux)
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CPPFLAGS += -DNDEBUG -DSYSDEBUG -DSUPPORT_VECTOR=1
 CONFIG_CCFLAGS += -O3 -fmerge-all-constants
 CONFIG_COPTS += -mred-zone
@@ -140,7 +140,7 @@ endif
 #
 ifeq ($(MODE), asan)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CPPFLAGS += -D__SANITIZE_ADDRESS__
 CONFIG_CCFLAGS += $(BACKTRACES) -O2 -DSYSDEBUG
 CONFIG_COPTS += -fsanitize=address
@@ -160,7 +160,7 @@ endif
 #
 ifeq ($(MODE), dbg)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CPPFLAGS += -DMODE_DBG -D__SANITIZE_ADDRESS__ -D__SANITIZE_UNDEFINED__
 CONFIG_CCFLAGS += $(BACKTRACES) -DSYSDEBUG -O0 -fno-inline
 CONFIG_COPTS += -fsanitize=address -fsanitize=undefined
@@ -170,7 +170,7 @@ QUOTA ?= -C64 -L300
 endif
 ifeq ($(MODE), aarch64-dbg)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CPPFLAGS += -DMODE_DBG -D__SANITIZE_UNDEFINED__
 CONFIG_CCFLAGS += $(BACKTRACES) -DSYSDEBUG -O0 -fno-inline -fdce
 CONFIG_COPTS += -fsanitize=undefined
@@ -189,7 +189,7 @@ endif
 #
 ifeq ($(MODE), sysv)
 ENABLE_FTRACE = 1
-CONFIG_OFLAGS ?= -g
+CONFIG_OFLAGS ?= -g -ggdb
 CONFIG_CCFLAGS += $(BACKTRACES) -O2
 CONFIG_CPPFLAGS += -DSYSDEBUG -DSUPPORT_VECTOR=121
 TARGET_ARCH ?= -msse3

libc/calls/BUILD.mk

@@ -147,6 +147,13 @@ o/$(MODE)/libc/calls/pledge-linux.o: private		\
 			-fPIC				\
 			-ffreestanding
 
+# we want -Os because:
+#   it makes a big difference
+#   it gets called very rarely
+o/$(MODE)/libc/calls/sigcrashsig.o: private		\
+		CFLAGS +=				\
+			-Os
+
 # these assembly files are safe to build on aarch64
 o/$(MODE)/libc/calls/getcontext.o: libc/calls/getcontext.S
 	@$(COMPILE) -AOBJECTIFY.S $(OBJECTIFY.S) $(OUTPUT_OPTION) -c $<

libc/calls/sig.c

@@ -301,7 +301,7 @@ static textwindows wontreturn void __sig_tramp(struct SignalFrame *sf) {
 }
 
 // sends signal to another specific thread which is ref'd
-static int __sig_killer(struct PosixThread *pt, int sig, int sic) {
+static textwindows int __sig_killer(struct PosixThread *pt, int sig, int sic) {
   unsigned rva = __sighandrvas[sig];
   unsigned flags = __sighandflags[sig];
 
@@ -462,66 +462,7 @@ textwindows void __sig_generate(int sig, int sic) {
   ALLOW_SIGNALS;
 }
 
-static int __sig_crash_sig(struct NtExceptionPointers *ep, int *code) {
-  switch (ep->ExceptionRecord->ExceptionCode) {
-    case kNtSignalBreakpoint:
-      *code = TRAP_BRKPT;
-      return SIGTRAP;
-    case kNtSignalIllegalInstruction:
-      *code = ILL_ILLOPC;
-      return SIGILL;
-    case kNtSignalPrivInstruction:
-      *code = ILL_PRVOPC;
-      return SIGILL;
-    case kNtSignalInPageError:
-    case kNtStatusStackOverflow:
-      *code = SEGV_MAPERR;
-      return SIGSEGV;
-    case kNtSignalGuardPage:
-    case kNtSignalAccessViolation:
-      *code = SEGV_ACCERR;
-      return SIGSEGV;
-    case kNtSignalInvalidHandle:
-    case kNtSignalInvalidParameter:
-    case kNtSignalAssertionFailure:
-      *code = SI_USER;
-      return SIGABRT;
-    case kNtStatusIntegerOverflow:
-      *code = FPE_INTOVF;
-      return SIGFPE;
-    case kNtSignalFltDivideByZero:
-      *code = FPE_FLTDIV;
-      return SIGFPE;
-    case kNtSignalFltOverflow:
-      *code = FPE_FLTOVF;
-      return SIGFPE;
-    case kNtSignalFltUnderflow:
-      *code = FPE_FLTUND;
-      return SIGFPE;
-    case kNtSignalFltInexactResult:
-      *code = FPE_FLTRES;
-      return SIGFPE;
-    case kNtSignalFltDenormalOperand:
-    case kNtSignalFltInvalidOperation:
-    case kNtSignalFltStackCheck:
-    case kNtSignalIntegerDivideByZero:
-    case kNtSignalFloatMultipleFaults:
-    case kNtSignalFloatMultipleTraps:
-      *code = FPE_FLTINV;
-      return SIGFPE;
-    case kNtSignalDllNotFound:
-    case kNtSignalOrdinalNotFound:
-    case kNtSignalEntrypointNotFound:
-    case kNtSignalDllInitFailed:
-      *code = SI_KERNEL;
-      return SIGSYS;
-    default:
-      *code = ep->ExceptionRecord->ExceptionCode;
-      return SIGSEGV;
-  }
-}
-
-static char *__sig_stpcpy(char *d, const char *s) {
+static textwindows char *__sig_stpcpy(char *d, const char *s) {
   size_t i;
   for (i = 0;; ++i) {
     if (!(d[i] = s[i])) {
@@ -530,8 +471,24 @@ static char *__sig_stpcpy(char *d, const char *s) {
   }
 }
 
-static void __sig_unmaskable(struct NtExceptionPointers *ep, int code, int sig,
-                             struct CosmoTib *tib) {
+static textwindows wontreturn void __sig_death(int sig, const char *thing) {
+#ifndef TINY
+  intptr_t hStderr;
+  char sigbuf[21], s[128], *p;
+  hStderr = GetStdHandle(kNtStdErrorHandle);
+  p = __sig_stpcpy(s, "Terminating on ");
+  p = __sig_stpcpy(p, thing);
+  p = __sig_stpcpy(p, strsignal_r(sig, sigbuf));
+  p = __sig_stpcpy(p,
+                   ". Pass --strace and/or ShowCrashReports() for details.\n");
+  WriteFile(hStderr, s, p - s, 0, 0);
+#endif
+  __sig_terminate(sig);
+}
+
+static textwindows void __sig_unmaskable(struct NtExceptionPointers *ep,
+                                         int code, int sig,
+                                         struct CosmoTib *tib) {
 
   // log vital crash information reliably for --strace before doing much
   // we don't print this without the flag since raw numbers scare people
@@ -549,17 +506,7 @@ static void __sig_unmaskable(struct NtExceptionPointers *ep, int code, int sig,
   // exception, then print a friendly helpful hint message to stderr
   unsigned rva = __sighandrvas[sig];
   if (rva == (intptr_t)SIG_DFL || rva == (intptr_t)SIG_IGN) {
-#ifndef TINY
-    intptr_t hStderr;
-    char sigbuf[21], s[128], *p;
-    hStderr = GetStdHandle(kNtStdErrorHandle);
-    p = __sig_stpcpy(s, "Terminating on uncaught ");
-    p = __sig_stpcpy(p, strsignal_r(sig, sigbuf));
-    p = __sig_stpcpy(
-        p, ". Pass --strace and/or ShowCrashReports() for details.\n");
-    WriteFile(hStderr, s, p - s, 0, 0);
-#endif
-    __sig_terminate(sig);
+    __sig_death(sig, "uncaught ");
   }
 
   // if this signal handler is configured to auto-reset to the default
@@ -580,8 +527,9 @@ static void __sig_unmaskable(struct NtExceptionPointers *ep, int code, int sig,
   }
 
   // call the user signal handler
-  // with a temporarily replaced signal mask
   // and a modifiable view of the faulting code's cpu state
+  // temporarily replace signal mask while calling crash handler
+  // abort process if sig is already blocked to avoid crash loop
   // note ucontext_t is a hefty data structures on top of NtContext
   ucontext_t ctx = {0};
   siginfo_t si = {.si_signo = sig, .si_code = code, .si_addr = si_addr};
@@ -591,6 +539,10 @@ static void __sig_unmaskable(struct NtExceptionPointers *ep, int code, int sig,
     blocksigs |= 1ull << (sig - 1);
   ctx.uc_sigmask = atomic_fetch_or_explicit(&tib->tib_sigmask, blocksigs,
                                             memory_order_acquire);
+  if (ctx.uc_sigmask & (1ull << (sig - 1))) {
+    __sig_death(sig, "masked ");
+    __sig_terminate(sig);
+  }
   __sig_handler(rva)(sig, &si, &ctx);
   atomic_store_explicit(&tib->tib_sigmask, ctx.uc_sigmask,
                         memory_order_release);

libc/calls/sig.internal.h

@@ -1,6 +1,7 @@
 #ifndef COSMOPOLITAN_LIBC_CALLS_SIGNALS_INTERNAL_H_
 #define COSMOPOLITAN_LIBC_CALLS_SIGNALS_INTERNAL_H_
 #include "libc/calls/struct/sigset.h"
+#include "libc/nt/struct/ntexceptionpointers.h"
 #include "libc/thread/posixthread.internal.h"
 
 #define SIG_HANDLED_NO_RESTART 1
@@ -17,11 +18,12 @@ extern struct Signals __sig;
 
 bool __sig_ignored(int);
 int __sig_check(void);
+int __sig_crash_sig(struct NtExceptionPointers *, int *);
+int __sig_get(sigset_t);
 int __sig_kill(struct PosixThread *, int, int);
 int __sig_mask(int, const sigset_t *, sigset_t *);
-int __sig_relay(int, int, sigset_t);
 int __sig_raise(int, int);
-int __sig_get(sigset_t);
+int __sig_relay(int, int, sigset_t);
 void __sig_delete(int);
 void __sig_generate(int, int);
 void __sig_init(void);

libc/calls/sigcrashsig.c

@@ -0,0 +1,107 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2024 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/sig.internal.h"
+#include "libc/intrin/pushpop.internal.h"
+#include "libc/nt/enum/signal.h"
+#include "libc/nt/enum/status.h"
+#include "libc/nt/struct/ntexceptionpointers.h"
+
+// this is all a mandatory dependency of winmain
+// so, we trade away maintanibility for tininess
+// see libc/sysv/consts.sh for canonical magnums
+
+#define SIGILL_  pushpop(4)
+#define SIGTRAP_ pushpop(5)
+#define SIGABRT_ pushpop(6)
+#define SIGFPE_  pushpop(8)
+#define SIGSEGV_ pushpop(11)
+#define SIGSYS_  pushpop(31)
+
+#define TRAP_BRKPT_  pushpop(1)
+#define ILL_ILLOPC_  pushpop(1)
+#define ILL_PRVOPC_  pushpop(5)
+#define SEGV_MAPERR_ pushpop(1)
+#define SEGV_ACCERR_ pushpop(2)
+#define SI_USER_     pushpop(0)
+#define FPE_FLTDIV_  pushpop(3)
+#define FPE_FLTOVF_  pushpop(4)
+#define FPE_INTOVF_  pushpop(2)
+#define FPE_FLTUND_  pushpop(5)
+#define FPE_FLTRES_  pushpop(6)
+#define FPE_FLTINV_  pushpop(7)
+#define SI_KERNEL_   0x80
+
+textwindows int __sig_crash_sig(struct NtExceptionPointers *ep, int *code) {
+  switch (ep->ExceptionRecord->ExceptionCode) {
+    case kNtSignalBreakpoint:
+      *code = TRAP_BRKPT_;
+      return SIGTRAP_;
+    case kNtSignalIllegalInstruction:
+      *code = ILL_ILLOPC_;
+      return SIGILL_;
+    case kNtSignalPrivInstruction:
+      *code = ILL_PRVOPC_;
+      return SIGILL_;
+    case kNtSignalInPageError:
+    case kNtStatusStackOverflow:
+      *code = SEGV_MAPERR_;
+      return SIGSEGV_;
+    case kNtSignalGuardPage:
+    case kNtSignalAccessViolation:
+      *code = SEGV_ACCERR_;
+      return SIGSEGV_;
+    case kNtSignalInvalidHandle:
+    case kNtSignalInvalidParameter:
+    case kNtSignalAssertionFailure:
+      *code = SI_USER_;
+      return SIGABRT_;
+    case kNtStatusIntegerOverflow:
+      *code = FPE_INTOVF_;
+      return SIGFPE_;
+    case kNtSignalFltDivideByZero:
+      *code = FPE_FLTDIV_;
+      return SIGFPE_;
+    case kNtSignalFltOverflow:
+      *code = FPE_FLTOVF_;
+      return SIGFPE_;
+    case kNtSignalFltUnderflow:
+      *code = FPE_FLTUND_;
+      return SIGFPE_;
+    case kNtSignalFltInexactResult:
+      *code = FPE_FLTRES_;
+      return SIGFPE_;
+    case kNtSignalFltDenormalOperand:
+    case kNtSignalFltInvalidOperation:
+    case kNtSignalFltStackCheck:
+    case kNtSignalIntegerDivideByZero:
+    case kNtSignalFloatMultipleFaults:
+    case kNtSignalFloatMultipleTraps:
+      *code = FPE_FLTINV_;
+      return SIGFPE_;
+    case kNtSignalDllNotFound:
+    case kNtSignalOrdinalNotFound:
+    case kNtSignalEntrypointNotFound:
+    case kNtSignalDllInitFailed:
+      *code = SI_KERNEL_;
+      return SIGSYS_;
+    default:
+      *code = ep->ExceptionRecord->ExceptionCode;
+      return SIGSEGV_;
+  }
+}