Messages in this thread | | | Date | Sun, 12 Oct 2014 12:00:03 -0500 | From | Jeff Epler <> | Subject | Re: [PATCH] x86: Clean up stack access code in irq_32.c |
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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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