Hi folks,
The attached testcase dies on Debian (amd64) if
compiled with -O2.
Here is the usual data:
% gcc -v
Using built-in specs.
Target: x86_64-linux
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr
--libexecdir=/usr/lib --enable-shared --with-system-zlib --enable-nls
--enable-threads=posix --without-included-gettext --program-suffix=-4.0
--enable-__cxa_atexit --enable-libstdcxx-allocator=mt
--enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm
--enable-java-awt=gtk --enable-mpfr --disable-werror --enable-checking=release
x86_64-linux
Thread model: posix
gcc version 4.0.0 (Debian 4.0.0-1)
% gcc -O -o testcase testcase.c
% ./testcase
Data: 42
% gcc -O2 -o testcase testcase.c
% ./testcase
Segmentation fault (core dumped)
The testcase has been created by grabbing some code
fragments from libX11, XFree86 4.3 on Debian, amd64.
-Wall complains about dereferencing type-punned pointer.
Is this a known problem? I haven't seen it in the database.
Regards
Harri
#include stdio.h
typedef struct _XDisplay Display;
typedef union {
Display *display;
void *gc;
void *visual;
void *screen;
void *pixmap_format;
void *font; } XEDataObject;
typedef struct _XExtData {
int number; /* number returned by XRegisterExtension */
struct _XExtData *next; /* next item on list of data for structure */
int (*free_private)( /* called to free private storage */
struct _XExtData *extension
);
void * private_data; /* data private to this extension. */
} XExtData;
struct _XDisplay
{
XExtData *ext_data; /* hook for extension to hang data */
int data; /* Network socket. */
};
XExtData **XEHeadOfExtensionList(object)
XEDataObject object;
{
return *(XExtData ***)object;
}
void _XF86BigfontCodes (dpy)
register Display *dpy;
{
XEDataObject dpy_union;
XExtData **pData;
dpy_union.display = dpy;
pData = XEHeadOfExtensionList(dpy_union);
printf(Data: %d\n, (*pData)-number);
}
int main()
{
XExtData extdata_in_main;
Display dpy = {
extdata_in_main,
0xdeadbeef,
};
extdata_in_main.number = 42;
extdata_in_main.next = 0;
_XF86BigfontCodes(dpy);
return 0;
}
# 1 testcase.c
# 1 built-in
# 1 command line
# 1 testcase.c
# 1 /usr/include/stdio.h 1 3 4
# 28 /usr/include/stdio.h 3 4
# 1 /usr/include/features.h 1 3 4
# 308 /usr/include/features.h 3 4
# 1 /usr/include/sys/cdefs.h 1 3 4
# 309 /usr/include/features.h 2 3 4
# 331 /usr/include/features.h 3 4
# 1 /usr/include/gnu/stubs.h 1 3 4
# 332 /usr/include/features.h 2 3 4
# 29 /usr/include/stdio.h 2 3 4
# 1 /usr/lib/gcc/x86_64-linux/4.0.0/include/stddef.h 1 3 4
# 214 /usr/lib/gcc/x86_64-linux/4.0.0/include/stddef.h 3 4
typedef long unsigned int size_t;
# 35 /usr/include/stdio.h 2 3 4
# 1 /usr/include/bits/types.h 1 3 4
# 28 /usr/include/bits/types.h 3 4
# 1 /usr/include/bits/wordsize.h 1 3 4
# 29 /usr/include/bits/types.h 2 3 4
# 1 /usr/lib/gcc/x86_64-linux/4.0.0/include/stddef.h 1 3 4
# 32 /usr/include/bits/types.h 2 3 4
typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;
typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef signed short int __int16_t;
typedef unsigned short int __uint16_t;
typedef signed int __int32_t;
typedef unsigned int __uint32_t;
typedef signed long int __int64_t;
typedef unsigned long int __uint64_t;
typedef long int __quad_t;
typedef unsigned long int __u_quad_t;
# 129 /usr/include/bits/types.h 3 4
# 1 /usr/include/bits/typesizes.h 1 3 4
# 130 /usr/include/bits/types.h 2 3 4
__extension__ typedef unsigned long int __dev_t;
__extension__ typedef unsigned int __uid_t;
__extension__ typedef unsigned int __gid_t;
__extension__ typedef unsigned long int __ino_t;
__extension__ typedef unsigned long int __ino64_t;
__extension__ typedef unsigned int __mode_t;
__extension__ typedef unsigned long int __nlink_t;
__extension__ typedef long int __off_t;
__extension__ typedef long int __off64_t;
__extension__ typedef int __pid_t;
__extension__ typedef struct { int __val[2]; } __fsid_t;
__extension__ typedef long int __clock_t;
__extension__ typedef unsigned long int __rlim_t;
__extension__ typedef unsigned long int __rlim64_t;
__extension__ typedef unsigned int __id_t;
__extension__ typedef long int __time_t;
__extension__ typedef unsigned int __useconds_t;
__extension__ typedef long int __suseconds_t;
__extension__ typedef int __daddr_t;
__extension__ typedef long int __swblk_t;
__extension__ typedef int __key_t;
__extension__ typedef int __clockid_t;
__extension__ typedef void * __timer_t;
__extension__ typedef long int __blksize_t;
__extension__ typedef long int __blkcnt_t;
__extension__ typedef long int __blkcnt64_t;
__extension__ typedef unsigned long int __fsblkcnt_t;
__extension__ typedef unsigned long int __fsblkcnt64_t;
__extension__ typedef unsigned long int __fsfilcnt_t;
__extension__ typedef
