It looks like the proposed variant still miscompiles in clang 3.4 and 3.5, the
two versions I had handy to test.
I extracted your code to a simple standalone C translation unit and
inspected various compilers' results via objdump.
// cut here for cso.c
struct thread_info { long l[32]; }; // who knows
#define STACK_WARN (1024)
#define PAGE_SIZE (4096)
#define THREAD_SIZE_ORDER 2
#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
#define THREAD_SIZE_MASK (THREAD_SIZE - 1)
#define CURRENT_MASK (~THREAD_SIZE_MASK)
/* how to get the current stack pointer from C */
#define current_stack_pointer ({ \
register unsigned long sp asm("esp"); \
sp; \
})
int check_stack_overflow0(void)
{
long sp;
__asm__ __volatile__("andl %%esp,%0" :
"=r" (sp) : "0" (THREAD_SIZE - 1));
return sp < (sizeof(struct thread_info) + STACK_WARN);
}
int check_stack_overflow1(void)
{
return (current_stack_pointer & THREAD_SIZE_MASK)
< sizeof(struct thread_info) + STACK_WARN;
}
// end cso.c
Typical compiler invocation:
clang-3.5 -m32 -Os -c cso.c
Both clang-3.4 and clang-3.5 as packaged for debian jessie seem to get
check_stack_overflow1 wrong, yielding a function which always returns true:
00000000 <check_stack_overflow1>:
0: b8 01 00 00 00 mov $0x1,%eax
5: c3 ret
Jeff
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