Messages in this thread | | | From | "Petr Vandrovec" <> | Date | Wed, 2 Jan 2002 18:40:24 +0100 | Subject | Re: [PATCH] C undefined behavior fix |
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On 2 Jan 02 at 11:45, Paul Koning wrote: > > It might be interesting for the compiler to warn about this coding > error (since it presumably can detect it). But "fixing" the behavior > of undefined code seems like a strange thing to do.
It is even worse (gcc 2.95.4 20011223 (Debian prerelease), i386). Test code:
#include <string.h> char* dst; void main(void) { strcpy(dst, "test"+CONSTANT); }
# gcc -O2 -S test.c -DCONSTANT=10 test.c: In function `main': test.c:4: warning: offset outside bounds of constant string ... and compiler generated correct code (call to strcpy with "test"+10).
But: # gcc -O2 -S test.c -DCONSTANT=0x80000000 test.c: In function `main': test.c:4: warning: offset outside bounds of constant string gcc: Internal compiler error: program cc1 got fatal signal 11
(and for CONSTANT < 5 it of course generated correct code to fill dst with string contents; and yes, I know that code will sigsegv on run because of dst is not initialized - but it should die at runtime, not at compile time).
So we should definitely change RELOC(), or sooner or later gcc will die on such code :-(
Debian's gcc 3.0.3-1 generates: 0 <= CONSTANT <= 4: fills dst directly with constant 5 <= CONSTANT <= 0x7FFFFFFF: emit warnings + use strcpy() 0x80000000U <= CONSTANT <= 0xFFFFFFFFU: use strcpy() silently ... and it does not die. Best regards, Petr Vandrovec vandrove@vc.cvut.cz - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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