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Check for __builtin_unreachable at configure time

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Add a configure check for __builtin_unreachable instead of basing its
availability on the __GNUC__ version. On OS X using gcc (a real gcc, not the
bundled version that's just a gcc front-end) leads to a linker assertion:

    https://github.com/jemalloc/jemalloc/issues/266

It turns out that this is caused by a gcc bug resulting from the use of
__builtin_unreachable():

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57438

To work around this bug, check that __builtin_unreachable() actually works at
configure time, and if it doesn't use abort() instead. The check is based on
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57438#c21.

With this `make check` passes with a homebrew installed gcc-5 and gcc-6.
This commit is contained in:
Elliot Ronaghan 2016-06-17 13:28:39 -07:00 • committed by Jason Evans
parent ae3314785b
commit 1167e9eff3
3 changed files with 29 additions and 16 deletions
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17
configure.ac
View file

@ -1038,6 +1038,23 @@ if test "x$enable_cache_oblivious" = "x1" ; then
fi
AC_SUBST([enable_cache_oblivious])
JE_COMPILABLE([a program using __builtin_unreachable], [
void foo (void) {
__builtin_unreachable();
}
], [
{
foo();
}
], [je_cv_gcc_builtin_unreachable])
if test "x${je_cv_gcc_builtin_ffsl}" = "xyes" ; then
AC_DEFINE([JEMALLOC_INTERNAL_UNREACHABLE], [__builtin_unreachable])
else
AC_DEFINE([JEMALLOC_INTERNAL_UNREACHABLE], [abort])
fi
dnl ============================================================================
dnl Check for __builtin_ffsl(), then ffsl(3), and fail if neither are found.
dnl One of those two functions should (theoretically) exist on all platforms

6
include/jemalloc/internal/jemalloc_internal_defs.h.in
View file

@ -185,6 +185,12 @@
/* TLS is used to map arenas and magazine caches to threads. */
#undef JEMALLOC_TLS
/*
* Used to mark unreachable code to quiet "end of non-void" compiler warnings.
* Don't use this directly; instead use unreachable() from util.h
*/
#undef JEMALLOC_INTERNAL_UNREACHABLE
/*
* ffs*() functions to use for bitmapping. Don't use these directly; instead,
* use ffs_*() from util.h.

22
include/jemalloc/internal/util.h
View file

@ -61,30 +61,20 @@
# define JEMALLOC_CC_SILENCE_INIT(v)
#endif
#define JEMALLOC_GNUC_PREREQ(major, minor) \
(!defined(__clang__) && \
(__GNUC__ > (major) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor))))
#ifndef __has_builtin
# define __has_builtin(builtin) (0)
#endif
#define JEMALLOC_CLANG_HAS_BUILTIN(builtin) \
(defined(__clang__) && __has_builtin(builtin))
#ifdef __GNUC__
# define likely(x) __builtin_expect(!!(x), 1)
# define unlikely(x) __builtin_expect(!!(x), 0)
# if JEMALLOC_GNUC_PREREQ(4, 6) || \
JEMALLOC_CLANG_HAS_BUILTIN(__builtin_unreachable)
# define unreachable() __builtin_unreachable()
# else
# define unreachable() abort()
# endif
#else
# define likely(x) !!(x)
# define unlikely(x) !!(x)
# define unreachable() abort()
#endif
#if !defined(JEMALLOC_INTERNAL_UNREACHABLE)
# error JEMALLOC_INTERNAL_UNREACHABLE should have been defined by configure
#endif
#define unreachable() JEMALLOC_INTERNAL_UNREACHABLE()
#include "jemalloc/internal/assert.h"
/* Use to assert a particular configuration, e.g., cassert(config_debug). */