NetBSD Problem Report #56940
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Date: Mon, 25 Jul 2022 22:30:48 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: libexecinfo fails to trace stack through signal trampoline for SIGSEGV call to null function pointer
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>Number: 56940
>Category: lib
>Synopsis: libexecinfo fails to trace stack through signal trampoline for SIGSEGV call to null function pointer
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: lib-bug-people
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Mon Jul 25 22:35:00 +0000 2022
>Last-Modified: Mon Jul 25 22:40:01 +0000 2022
>Originator: Taylor R Campbell
>Release: current
>Organization:
El Fundacion NetBSD
>Environment:
being consumed by an insatiable thirst for oil
>Description:
When invoked from a signal handler for the SIGSEGV delivered due to a call to a null function pointer, the backtrace(3) functions of libexecinfo bottom out at __sigtramp_siginfo_2 or equivalent, and fail to yield return addresses for the call site of the null function pointer or its callers.
The information is available -- for example, on amd64, r15 of the signal trampoline frame points to a ucontext_t structure with process state where rsp[0] holds the return address and &rsp[1] is where parent frame lives. But libunwind fails to find this information, and so the stack trace ends at the signal trampoline.
>How-To-Repeat:
#include <sys/cdefs.h>
#include <err.h>
#include <execinfo.h>
#include <setjmp.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
void (*f)(void);
jmp_buf env;
void *stack[64];
size_t stackdepth;
char **symbols;
void
sigsegv(int signo)
{
(void)signo;
stackdepth = backtrace(stack, __arraycount(stack));
longjmp(env, 1);
}
int
main(void)
{
size_t i;
if (signal(SIGSEGV, &sigsegv) == SIG_ERR)
err(1, "signal(SIGSEGV)");
if (setjmp(env) == 0)
(*f)();
symbols = backtrace_symbols(stack, stackdepth);
if (symbols == NULL)
err(1, "backtrace_symbols");
for (i = 0; i < stackdepth; i++)
printf("%s\n", symbols[i]);
fflush(stdout);
return ferror(stdout);
}
>Fix:
Yes, please!
>Audit-Trail:
From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc:
Subject: PR/56940 CVS commit: src/tests/lib/libexecinfo
Date: Mon, 25 Jul 2022 22:37:37 +0000
Module Name: src
Committed By: riastradh
Date: Mon Jul 25 22:37:37 UTC 2022
Modified Files:
src/tests/lib/libexecinfo: t_sig_backtrace.c
Log Message:
execinfo(3): Mark sig_backtrace_jump test as xfail.
PR lib/56940
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/tests/lib/libexecinfo/t_sig_backtrace.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
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