781457 - use of undeclared identifier '_Unwind_Backtrace'

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Jan Beich]

User Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:17.0) Gecko/17.0 Firefox/17.0
Build ID: 20120809002637

Steps to reproduce:

1. Installed libunwind
2. Tried to compile firefox with gcc42 or clang.


Actual results:

xpcom/base/nsStackWalk.cpp:1197:29: error: use of undeclared identifier '_Unwind_Backtrace'
    _Unwind_Reason_Code t = _Unwind_Backtrace(unwind_callback, &info);
                            ^
1 error generated.



Expected results:

Build succesfully.

Comment 1

[Jan Beich]

Attachment: define _GNU_SOURCE for _Unwind_Backtrace

Comment 2

[Jan Beich]

Comment on attachment 650465 [details] [diff] [review]
define _GNU_SOURCE for _Unwind_Backtrace

Unlike recent versions of GCC libunwind and libc++ put _Unwind_Backtrace under _GNU_SOURCE. However, configure script doesn't know this and just checks for the function in unwind.h irregardless of where it came from.

http://git.savannah.gnu.org/cgit/libunwind.git/tree/include/unwind.h
https://github.com/pathscale/libcxxrt/blob/master/src/unwind-itanium.h

Comment 3

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

How did configure detect the function's presence if it's conditional on _GNU_SOURCE?

(You deleted config.cache and reran configure when changing compilers, right?)

Comment 4

[Jan Beich]

(In reply to David Baron [:dbaron] from comment #3)
> How did configure detect the function's presence if it's conditional on _GNU_SOURCE?

Configure script checks only header presence[1]. Then it goes to check libraries and finds that implicitly linked -lgcc_s provides _Unwind_Backtrace symbol.

$ env -i PATH=$PATH gmake conftest -f /dev/null
cc     conftest.c   -o conftest

$ cat conftest.c
#line 24094 "configure"
#include "confdefs.h"
/* System header to define __stub macros and hopefully few prototypes,
    which can conflict with char _Unwind_Backtrace(); below.  */
#include <assert.h>
/* Override any gcc2 internal prototype to avoid an error.  */
/* We use char because int might match the return type of a gcc2
    builtin and then its argument prototype would still apply.  */
char _Unwind_Backtrace();

int main() {

/* The GNU C library defines this for functions which it implements
    to always fail with ENOSYS.  Some functions are actually named
    something starting with __ and the normal name is an alias.  */
#if defined (__stub__Unwind_Backtrace) || defined (__stub____Unwind_Backtrace)
choke me
#else
_Unwind_Backtrace();
#endif

; return 0; }


[1] more correct check would likely use AC_TRY_COMPILE, e.g.

dnl ========================================================
dnl = Support for gcc stack unwinding (from gcc 3.3)
dnl ========================================================
if test -z "$SKIP_LIBRARY_CHECKS"; then
    AC_LANG_CPLUSPLUS
    AC_MSG_CHECKING([for _Unwind_Backtrace in unwind.h])
    AC_TRY_COMPILE([#include <unwind.h>], [_Unwind_Backtrace(0,0)],
        AC_MSG_RESULT([found]),
        AC_TRY_COMPILE([#define _GNU_SOURCE
                #include <unwind.h>], [_Unwind_Backtrace(0,0)],
            AC_MSG_RESULT([needs -D_GNU_SOURCE]),
            AC_MSG_RESULT([not found])))
fi

Comment 5

[Jan Beich]

On FreeBSD it usually is Blender port that pulls libunwind by default (CAMERATRACK option).
http://www.freshports.org/graphics/blender

Comment 6

[Jan Beich]

Note, clang has unwind.h since 3.1. The header is different from the one used by -stdlib=libc++, it doesn't need _GNU_SOURCE.

http://clang.llvm.org/doxygen/unwind_8h_source.html

Comment 7

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Comment on attachment 650465 [details] [diff] [review]
define _GNU_SOURCE for _Unwind_Backtrace

r=dbaron

Comment 8

[Jan Beich]

Attachment: Bug 781457 - Define _GNU_SOURCE for _Unwind_Backtrace. r=dbaron

Comment 9

[Ryan VanderMeulen [:RyanVM]]

Green on Try:
https://tbpl.mozilla.org/?tree=Try&rev=1d57b70df30c

https://hg.mozilla.org/integration/mozilla-inbound/rev/115bed385a77

Comment 10

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/115bed385a77