https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82090
Bug ID: 82090
Summary: Bogus warning: ‘magic_p’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
[hjl@gnu-efi-2 tmp]$ cat foo.c
typedef int __libc_lock_t;
void malloc_printerr(const char *str) __attribute__ ((noreturn));
extern __libc_lock_t foo;
static void *
mem2chunk_check (void *mem, unsigned char **magic_p)
{
if (!mem)
return (( void *)0) ;
if (magic_p)
*magic_p = (unsigned char *) mem;
return mem;
}
void *
realloc_check (void *oldmem, unsigned int bytes, const void *caller)
{
unsigned char *magic_p;
void * oldp = mem2chunk_check (oldmem, &magic_p);
(void) ({ int ignore; if (__builtin_constant_p (0) && (0) == 0) __asm
__volatile ("cmpl $0, __libc_multiple_threads(%%rip)\n\t" "je 0f\n\t" "lock;
decl %0\n\t" "jne 1f\n\t" "jmp 24f\n\t" "0:\tdecl %0\n\t" "je 24f\n\t" "1:\tlea
%0, %%" "rdi" "\n" "2:\tsub $128, %%" "rsp" "\n" ".cfi_adjust_cfa_offset 128\n"
"3:\tcallq __lll_unlock_wake_private\n" "4:\tadd $128, %%" "rsp" "\n"
".cfi_adjust_cfa_offset -128\n" "24:" : "=m" (foo), "=&D" (ignore) : "m" (foo)
: "ax", "cx", "r11", "cc", "memory"); else __asm __volatile ("cmpl $0,
__libc_multiple_threads(%%rip)\n\t" "je 0f\n\t" "lock; decl %0\n\t" "jne
1f\n\t" "jmp 24f\n\t" "0:\tdecl %0\n\t" "je 24f\n\t" "1:\tlea %0, %%" "rdi"
"\n" "2:\tsub $128, %%" "rsp" "\n" ".cfi_adjust_cfa_offset 128\n" "3:\tcallq
__lll_unlock_wake\n" "4:\tadd $128, %%" "rsp" "\n" ".cfi_adjust_cfa_offset
-128\n" "24:" : "=m" (foo), "=&D" (ignore) : "m" (foo), "S" (0) : "ax", "cx",
"r11", "cc", "memory"); });
if (!oldp)
malloc_printerr ("realloc(): invalid pointer");
*magic_p ^= 0xFF;
return oldp;
}
[hjl@gnu-efi-2 tmp]$ gcc -Wall foo.c -S -O3
foo.c: In function ‘realloc_check’:
foo.c:25:12: warning: ‘magic_p’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
*magic_p ^= 0xFF;
~~~~~~~~~^~~~~~~
[hjl@gnu-efi-2 tmp]$
