uclibc: weak symbols -> SEGV

[Denis Vlasenko]

On Saturday 30 December 2006 02:20, Denis Vlasenko wrote:
>     if (likely(_locale_init!=NULL))
> {
> void *p = _locale_init;
> write(1, &p, 4);
> _exit(95);
>         _locale_init();
> }
> 
> Compiling with -S reveals that if() is optimized to if(1) -
> gcc thinks that _locale_init is never NULL. But it is -
> write() outputs four zero bytes if I compile and run this...

Okay, I think I nailed it down:

// Works: gcc -Os -S test.c
// Does NOT work: gcc -Os -S -fPIC test.c
// (tested with gcc 3.4.3 and 4.1.1)
// (weak without hidden works!)
void __attribute__ ((weak)) f(void) __attribute__ ((visibility ("hidden")));

int main(void) {
        if (f != 0)
                return 1;
        return 0;
}

Is it a bug in gcc? If not, maybe a #warning or #error is in order somewhere
so that people won't be bitten by this?

.config which has the right mix of option for this to happen is attached.
--
vda
-------------- next part --------------
#
# Automatically generated make config: don't edit
# Sat Dec 30 01:34:53 2006
#
# TARGET_alpha is not set
# TARGET_arm is not set
# TARGET_bfin is not set
# TARGET_cris is not set
# TARGET_e1 is not set
# TARGET_frv is not set
# TARGET_h8300 is not set
# TARGET_hppa is not set
TARGET_i386=y
# TARGET_i960 is not set
# TARGET_ia64 is not set
# TARGET_m68k is not set
# TARGET_microblaze is not set
# TARGET_mips is not set
# TARGET_nios is not set
# TARGET_nios2 is not set
# TARGET_powerpc is not set
# TARGET_sh is not set
# TARGET_sh64 is not set
# TARGET_sparc is not set
# TARGET_v850 is not set
# TARGET_vax is not set
# TARGET_x86_64 is not set

#
# Target Architecture Features and Options
#
TARGET_ARCH="i386"
FORCE_OPTIONS_FOR_ARCH=y
# CONFIG_GENERIC_386 is not set
# CONFIG_386 is not set
CONFIG_486=y
# CONFIG_586 is not set
# CONFIG_586MMX is not set
# CONFIG_686 is not set
# CONFIG_PENTIUMII is not set
# CONFIG_PENTIUMIII is not set
# CONFIG_PENTIUM4 is not set
# CONFIG_K6 is not set
# CONFIG_K7 is not set
# CONFIG_ELAN is not set
# CONFIG_CRUSOE is not set
# CONFIG_WINCHIPC6 is not set
# CONFIG_WINCHIP2 is not set
# CONFIG_CYRIXIII is not set
# CONFIG_NEHEMIAH is not set

#
# Using ELF file format
#
ARCH_LITTLE_ENDIAN=y

#
# Using Little Endian
#
ARCH_HAS_MMU=y
ARCH_USE_MMU=y
UCLIBC_HAS_FLOATS=y
UCLIBC_HAS_FPU=y
DO_C99_MATH=y
KERNEL_HEADERS="/usr/srcdevel/uclibc/uClibc/include_2.6.18.1"
HAVE_DOT_CONFIG=y

#
# General Library Settings
#
# HAVE_NO_PIC is not set
DOPIC=y
# HAVE_NO_SHARED is not set
# ARCH_HAS_NO_LDSO is not set
# HAVE_SHARED is not set
UCLIBC_CTOR_DTOR=y
# HAS_NO_THREADS is not set
UCLIBC_HAS_THREADS=y
# PTHREADS_DEBUG_SUPPORT is not set
LINUXTHREADS_OLD=y
UCLIBC_HAS_LFS=y
# MALLOC is not set
# MALLOC_SIMPLE is not set
MALLOC_STANDARD=y
# MALLOC_GLIBC_COMPAT is not set
UCLIBC_DYNAMIC_ATEXIT=y
# COMPAT_ATEXIT is not set
# UCLIBC_SUSV3_LEGACY is not set
# UCLIBC_SUSV3_LEGACY_MACROS is not set
UCLIBC_HAS_SHADOW=y
# UCLIBC_HAS_PROGRAM_INVOCATION_NAME is not set
UCLIBC_HAS___PROGNAME=y
UNIX98PTY_ONLY=y
ASSUME_DEVPTS=y
UCLIBC_HAS_TM_EXTENSIONS=y
UCLIBC_HAS_TZ_CACHING=y
UCLIBC_HAS_TZ_FILE=y
UCLIBC_HAS_TZ_FILE_READ_MANY=y
UCLIBC_TZ_FILE_PATH="/etc/TZ"

#
# Networking Support
#
UCLIBC_HAS_IPV6=y
UCLIBC_HAS_RPC=y
UCLIBC_HAS_FULL_RPC=y
UCLIBC_HAS_REENTRANT_RPC=y
# UCLIBC_USE_NETLINK is not set

#
# String and Stdio Support
#
UCLIBC_HAS_STRING_GENERIC_OPT=y
UCLIBC_HAS_STRING_ARCH_OPT=y
UCLIBC_HAS_CTYPE_TABLES=y
UCLIBC_HAS_CTYPE_SIGNED=y
UCLIBC_HAS_CTYPE_UNSAFE=y
# UCLIBC_HAS_CTYPE_CHECKED is not set
# UCLIBC_HAS_CTYPE_ENFORCED is not set
UCLIBC_HAS_WCHAR=y
UCLIBC_HAS_LOCALE=y
UCLIBC_PREGENERATED_LOCALE_DATA=y
# UCLIBC_DOWNLOAD_PREGENERATED_LOCALE_DATA is not set
# UCLIBC_HAS_XLOCALE is not set
# UCLIBC_HAS_HEXADECIMAL_FLOATS is not set
# UCLIBC_HAS_GLIBC_DIGIT_GROUPING is not set
# UCLIBC_HAS_GLIBC_CUSTOM_PRINTF is not set
UCLIBC_PRINTF_SCANF_POSITIONAL_ARGS=9
# UCLIBC_HAS_SCANF_GLIBC_A_FLAG is not set
# UCLIBC_HAS_STDIO_BUFSIZ_NONE is not set
# UCLIBC_HAS_STDIO_BUFSIZ_256 is not set
# UCLIBC_HAS_STDIO_BUFSIZ_512 is not set
# UCLIBC_HAS_STDIO_BUFSIZ_1024 is not set
# UCLIBC_HAS_STDIO_BUFSIZ_2048 is not set
UCLIBC_HAS_STDIO_BUFSIZ_4096=y
# UCLIBC_HAS_STDIO_BUFSIZ_8192 is not set
UCLIBC_HAS_STDIO_BUILTIN_BUFFER_NONE=y
# UCLIBC_HAS_STDIO_BUILTIN_BUFFER_4 is not set
# UCLIBC_HAS_STDIO_BUILTIN_BUFFER_8 is not set
# UCLIBC_HAS_STDIO_SHUTDOWN_ON_ABORT is not set
UCLIBC_HAS_STDIO_GETC_MACRO=y
UCLIBC_HAS_STDIO_PUTC_MACRO=y
UCLIBC_HAS_STDIO_AUTO_RW_TRANSITION=y
# UCLIBC_HAS_FOPEN_LARGEFILE_MODE is not set
# UCLIBC_HAS_FOPEN_EXCLUSIVE_MODE is not set
# UCLIBC_HAS_GLIBC_CUSTOM_STREAMS is not set
UCLIBC_HAS_PRINTF_M_SPEC=y
UCLIBC_HAS_ERRNO_MESSAGES=y
# UCLIBC_HAS_SYS_ERRLIST is not set
UCLIBC_HAS_SIGNUM_MESSAGES=y
# UCLIBC_HAS_SYS_SIGLIST is not set
UCLIBC_HAS_GNU_GETOPT=y
UCLIBC_HAS_GNU_GETSUBOPT=y

#
# Big and Tall
#
UCLIBC_HAS_REGEX=y
UCLIBC_HAS_REGEX_OLD=y
UCLIBC_HAS_FNMATCH=y
UCLIBC_HAS_FNMATCH_OLD=y
UCLIBC_HAS_WORDEXP=y
UCLIBC_HAS_FTW=y
UCLIBC_HAS_GLOB=y
# UCLIBC_HAS_GNU_GLOB is not set

#
# Library Installation Options
#
RUNTIME_PREFIX="/usr/$(TARGET_ARCH)-linux-uclibc/"
DEVEL_PREFIX="/usr/$(TARGET_ARCH)-linux-uclibc/usr/"

#
# Security options
#
# UCLIBC_HAS_ARC4RANDOM is not set
# HAVE_NO_SSP is not set
# UCLIBC_HAS_SSP is not set
UCLIBC_BUILD_NOEXECSTACK=y

#
# uClibc development/debugging options
#
CROSS_COMPILER_PREFIX=""
# DODEBUG is not set
# DODEBUG_PT is not set
DOSTRIP=y
# DOASSERTS is not set
# UCLIBC_MALLOC_DEBUGGING is not set
WARNINGS="-Wall"
# EXTRA_WARNINGS is not set
# DOMULTI is not set
# UCLIBC_MJN3_ONLY is not set