Improve assert() failure output (#956)

Changes:
- _ast_assertfail(): Use glibc's backtrace() and
  backtrace_symbols() to produce a backtrace after a failed
  assertion.
  - Compile with -rdynamic or -Wl,-export-dynamic when available.
    Glibc's backtrace_symbols() function will fail to print
    readable function names if this is not included in the linker's
    flags, resulting in significantly worse backtraces. (This flag
    should've been part of #357,
    but it appears to have been forgotten about/omitted
    accidentally.)
- nv_endsubscript(): Add an error message prior to calling assert
  to hopefully make the intermittent crashing bug easier to trace
  (I can't trigger it manually at all, so hopefully the next CI
  crash produces more useful output.)
- ci.yml: Compile CI builds with CCFLAGS=-Og and LDFLAGS=-g
  (required alongside -rdynamic for useful backtraces).

Author: JohnoKing

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     - name: Checkout sources
       uses: actions/checkout@main
     - name: Build
-      run: bin/package make -j5
+      run: bin/package make -j5 CCFLAGS=-Og
     - name: Regression tests
       run: |
         PS4="$PS4[ci.yml] "
@@ -30,13 +30,13 @@ jobs:
         sed --regexp-extended --in-place=.orig \
           '/^SHOPT (AUDIT|BGX|BRACEPAT|DEVFD|DYNAMIC|EDPREDICT|ESH|FIXEDARRAY|HISTEXPAND|MULTIBYTE|NAMESPACE|OPTIMIZE|SPAWN|STATS|SUID_EXEC|VSH)=/ s/=1?/=0/' \
           src/cmd/ksh93/SHOPT.sh &&
-        bin/package make -j5 &&
+        bin/package make -j5 CCFLAGS=-Og &&
         : default regression tests with SHOPTs disabled &&
         script -q -e -c "bin/shtests" &&
         : enable SHOPT_SCRIPTONLY, rebuild ksh &&
         sed --regexp-extended --in-place=.orig \
           '/^SHOPT SCRIPTONLY=/ s/=0?/=1/' \
           src/cmd/ksh93/SHOPT.sh &&
-        bin/package make -j5 &&
+        bin/package make -j5 CCFLAGS=-Og &&
         : default regression tests with SHOPT_SCRIPTONLY enabled &&
         script -q -e -c "bin/shtests"

src/cmd/builtin/Mamfile

@@ -9,7 +9,7 @@ setv INSTALLROOT ../../..
 setv CC cc
 setv mam_cc_FLAGS %{mam_cc_TARGET} %{mam_cc_DLL} %{-debug-symbols?1?%{mam_cc_DEBUG} -D_BLD_DEBUG?%{mam_cc_OPTIMIZE}?}
 setv CCFLAGS
-setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??}
+setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??} %{mam_cc_EXPORT_DYNAMIC}
 setv IFFEFLAGS
 setv LDFLAGS
 

src/cmd/ksh93/Mamfile

@@ -8,7 +8,7 @@ setv INSTALLROOT ../../..
 setv CC cc
 setv mam_cc_FLAGS %{mam_cc_TARGET} %{mam_cc_DLL} -D_BLD_ksh %{-debug-symbols?1?%{mam_cc_DEBUG} -D_BLD_DEBUG?%{mam_cc_OPTIMIZE}?}
 setv CCFLAGS
-setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??}
+setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??} %{mam_cc_EXPORT_DYNAMIC}
 setv IFFEFLAGS
 setv LDFLAGS
 setv SH_DICT \"libshell\"

src/cmd/ksh93/sh/array.c

@@ -1483,6 +1483,8 @@ char *nv_endsubscript(Namval_t *np, char *cp, int mode)
 {
 	int count=1, quoted=0, c;
 	char *sp = cp+1;
+	if(*cp!='[')
+		errormsg(SH_DICT, ERROR_exit(0), "Failure: *cp == %c, cp == '%s'", *cp, cp);
 	assert(*cp=='[');
 	/* first find matching ']' */
 	while(count>0 && (c= *++cp))

src/lib/libast/Mamfile

@@ -10,7 +10,7 @@ setv INCLUDE_AST %{INSTALLROOT}/include/ast
 setv CC cc
 setv mam_cc_FLAGS %{mam_cc_TARGET} %{mam_cc_DLL} -D_BLD_ast %{-debug-symbols?1?%{mam_cc_DEBUG} -D_BLD_DEBUG?%{mam_cc_OPTIMIZE}?}
 setv CCFLAGS
-setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??}
+setv CCLDFLAGS %{-strip-symbols?1?%{mam_cc_LD_STRIP}??} %{mam_cc_EXPORT_DYNAMIC}
 setv IFFEFLAGS
 setv LDFLAGS
 setv DYLIB_PRE %{mam_cc_SUFFIX_DYNAMIC?*?%{mam_cc_PREFIX_DYNAMIC}?%{mam_cc_PREFIX_SHARED}?}

src/lib/libast/comp/assert.c

@@ -16,13 +16,32 @@
 
 #include <ast.h>
 
+#if _hdr_execinfo
+#include <execinfo.h>
+#endif
+
 noreturn void _ast_assertfail(const char *a, const char *fun, const char *file, int line)
 {
 #if _has___func__ || _has___FUNCTION__
 	sfprintf(sfstderr,"\n*** assertion %s failed in %s(), %s:%d\n", a, fun, file, line);
 #else
 	NOT_USED(fun);
 	sfprintf(sfstderr,"\n*** assertion %s failed in %s:%d\n", a, file, line);
+#endif
+#if _lib_backtrace && _lib_backtrace_symbols
+	{
+		void* callstack[200];
+		int i, frames = backtrace(callstack, 200);
+		char** strs = backtrace_symbols(callstack, frames);
+		if(strs)
+		{
+			for (i = 0; i < frames; ++i)
+				sfprintf(sfstderr, "%s\n", strs[i]);
+			free(strs);
+		}
+		else
+			sfprintf(sfstderr, "Could not obtain a backtrace (%s)\n", strerror(errno));
+	}
 #endif
 	sfsync(NULL);
 	abort();

src/lib/libast/features/lib

@@ -4,7 +4,7 @@ cmd	universe
 
 sys	mman
 hdr	fcntl,dirent,direntry,filio,fnmatch,jioctl,libgen,limits
-hdr	locale,ndir,nl_types,process,spawn,utime
+hdr	execinfo,locale,ndir,nl_types,process,spawn,utime
 hdr	linux/fs,linux/msdos_fs
 hdr	wctype
 hdr	wchar note{ <wchar.h> and isw*() really work }end execute{
@@ -24,7 +24,7 @@ dat	_tzname,tzname
 
 lib	BSDsetpgrp
 lib	_cleanup
-lib	bcopy,bzero,confstr,dirread
+lib	backtrace,backtrace_symbols,bcopy,bzero,confstr,dirread
 lib	fchmod,fcntl,fnmatch,fork,fsync
 lib	getconf,getdents,getdirentries,getdtablesize
 lib	gethostname,getpagesize,getrlimit,getuniverse

src/lib/libcmd/Mamfile

@@ -10,7 +10,7 @@ setv mam_cc_FLAGS %{mam_cc_TARGET} %{mam_cc_DLL} %{-debug-symbols?1?%{mam_cc_DEB
 setv CCFLAGS
 setv IFFEFLAGS
 setv LDFLAGS
-setv CCLDFLAGS
+setv CCLDFLAGS %{mam_cc_EXPORT_DYNAMIC}
 setv DYLIB_PRE %{mam_cc_SUFFIX_DYNAMIC?*?%{mam_cc_PREFIX_DYNAMIC}?%{mam_cc_PREFIX_SHARED}?}
 setv DYLIB_SUF %{mam_cc_SUFFIX_DYNAMIC-%{mam_cc_SUFFIX_SHARED}}
 setv DYLIB_VERSION 4.0

src/lib/libdll/Mamfile

@@ -10,7 +10,7 @@ setv mam_cc_FLAGS %{mam_cc_TARGET} %{mam_cc_DLL} %{-debug-symbols?1?%{mam_cc_DEB
 setv CCFLAGS
 setv IFFEFLAGS
 setv LDFLAGS
-setv CCLDFLAGS
+setv CCLDFLAGS %{mam_cc_EXPORT_DYNAMIC}
 setv DYLIB_PRE %{mam_cc_SUFFIX_DYNAMIC?*?%{mam_cc_PREFIX_DYNAMIC}?%{mam_cc_PREFIX_SHARED}?}
 setv DYLIB_SUF %{mam_cc_SUFFIX_DYNAMIC-%{mam_cc_SUFFIX_SHARED}}
 setv DYLIB_VERSION 4.0