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Unix crash log: handle SIGSEGVs while backtracing. Add documentation.

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This commit is contained in:
Jonathan G Rennison
2015-09-09 18:28:03 +01:00
parent b9f5765415
commit eaf9aa6571
1 changed files with 72 additions and 6 deletions
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78
src/os/unix/crashlog_unix.cpp
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@@ -19,6 +19,7 @@
#include <errno.h>
#include <signal.h>
#include <sys/utsname.h>
#include <setjmp.h>
#if defined(__GLIBC__)
/* Execinfo (and thus making stacktraces) is a GNU extension */
@@ -43,6 +44,21 @@
#include "../../safeguards.h"
#if defined(__GLIBC__) && defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
#pragma GCC diagnostic ignored "-Wclobbered"
#endif
#if defined(__GLIBC__)
static char *logStacktraceSavedBuffer;
static jmp_buf logStacktraceJmpBuf;
static void LogStacktraceSigSegvHandler(int sig)
{
signal(SIGSEGV, SIG_DFL);
longjmp(logStacktraceJmpBuf, 1);
}
#endif
/**
* Unix implementation for the crash logger.
*/
@@ -115,17 +131,60 @@ class CrashLogUnix : public CrashLog {
}
#endif
/**
* Get a stack backtrace of the current thread's stack.
*
* This has several modes/options, the most full-featured/complex of which is GLIBC mode.
*
* This gets the backtrace using backtrace() and backtrace_symbols().
* backtrace() is prone to crashing if the stack is invalid.
* Also these functions freely use malloc which is not technically OK in a signal handler, as
* malloc is not re-entrant.
* For that reason, set up another SIGSEGV handler to handle the case where we trigger a SIGSEGV
* during the course of getting the backtrace.
*
* If libdl is present, try to use that to get the section file name and possibly the symbol
* name/address instead of using the string from backtrace_symbols().
* If libdl and libbfd are present, try to use that to get the symbol name/address using the
* section file name returned from libdl. This is becuase libbfd also does line numbers,
* and knows about more symbols than libdl does.
* If demangling support is available, try to demangle whatever symbol name we got back.
* If we could find a symbol address from libdl or libbfd, show the offset from that to the frame address.
*
* Note that GCC complains about 'buffer' being clobbered by the longjmp.
* This is not an issue as we save/restore it explicitly, so silence the warning.
*/
/* virtual */ char *LogStacktrace(char *buffer, const char *last) const
{
buffer += seprintf(buffer, last, "Stacktrace:\n");
#if defined(__GLIBC__)
#if defined(WITH_BFD)
bfd_init();
#endif
logStacktraceSavedBuffer = buffer;
if (setjmp(logStacktraceJmpBuf) != 0) {
buffer = logStacktraceSavedBuffer;
buffer += seprintf(buffer, last, "\nSomething went seriously wrong when attempting to decode the stacktrace (SIGSEGV in signal handler)\n");
buffer += seprintf(buffer, last, "This is probably due to either: a crash caused by an attempt to call an invalid function\n");
buffer += seprintf(buffer, last, "pointer, some form of stack corruption, or an attempt was made to call malloc recursively.\n\n");
return buffer;
}
signal(SIGSEGV, LogStacktraceSigSegvHandler);
sigset_t sigs;
sigset_t oldsigs;
sigemptyset(&sigs);
sigaddset(&sigs, SIGSEGV);
sigprocmask(SIG_UNBLOCK, &sigs, &oldsigs);
void *trace[64];
int trace_size = backtrace(trace, lengthof(trace));
char **messages = backtrace_symbols(trace, trace_size);
#if defined(WITH_BFD)
bfd_init();
#endif /* WITH_BFD */
for (int i = 0; i < trace_size; i++) {
#if defined(WITH_DL)
Dl_info info;
@@ -144,7 +203,7 @@ class CrashLogUnix : public CrashLog {
if (bfd_info.function_addr != 0) func_addr = reinterpret_cast<void *>(bfd_info.function_addr);
line_num = bfd_info.line;
}
#endif
#endif /* WITH_BFD */
bool ok = true;
const int ptr_str_size = (2 + sizeof(void*) * 2);
if (dladdr_result && func_name) {
@@ -152,7 +211,7 @@ class CrashLogUnix : public CrashLog {
char *demangled = NULL;
#if defined(WITH_DEMANGLE)
demangled = abi::__cxa_demangle(func_name, NULL, 0, &status);
#endif
#endif /* WITH_DEMANGLE */
const char *name = (demangled != NULL && status == 0) ? demangled : func_name;
buffer += seprintf(buffer, last, " [%02i] %*p %-40s %s + 0x%zx\n", i, ptr_str_size,
trace[i], info.dli_fname, name, (char *)trace[i] - (char *)func_addr);
@@ -167,10 +226,15 @@ class CrashLogUnix : public CrashLog {
buffer += seprintf(buffer, last, "%*s%s:%u\n", 7 + ptr_str_size, "", file_name, line_num);
}
if (ok) continue;
#endif
#endif /* WITH_DL */
buffer += seprintf(buffer, last, " [%02i] %s\n", i, messages[i]);
}
free(messages);
signal(SIGSEGV, SIG_DFL);
sigprocmask(SIG_SETMASK, &oldsigs, NULL);
/* end of __GLIBC__ */
#elif defined(SUNOS)
ucontext_t uc;
if (getcontext(&uc) != 0) {
@@ -180,6 +244,8 @@ class CrashLogUnix : public CrashLog {
StackWalkerParams wp = { &buffer, last, 0 };
walkcontext(&uc, &CrashLogUnix::SunOSStackWalker, &wp);
/* end of SUNOS */
#else
buffer += seprintf(buffer, last, " Not supported.\n");
#endif