Hello,
Here is the code snippet which caused compile-time error in bug 588:
typedef unsigned long int uintptr_t;
struct Header
{
int self;
uintptr_t stack_guard;
};
void foo(struct Header header, uintptr_t stack_chk_guard)
{
if (sizeof (header.stack_guard) == 1)
asm volatile ("movb %b0,%%fs:%P1" : : "iq" (stack_chk_guard),
"i" (__builtin_offsetof (struct Header, stack_guard)));
else if (sizeof (header.stack_guard) == 4)
asm volatile ("movl %0,%%fs:%P1" : : "ir" (stack_chk_guard), // error
"i" (__builtin_offsetof (struct Header, stack_guard)));
else
{
if (sizeof (header.stack_guard) !=8 )
abort ();
asm volatile ("movq %q0,%%fs:%P1" :
: "ir" ((unsigned long int) stack_chk_guard),
"i" (__builtin_offsetof (struct Header, stack_guard)));
}
}
In the case "sizeof (header.stack_guard) == 4", the operand constraint "ir"
specifies an integer register which is a 64 bit "r" register under a 64 bit
compilation, but a 64 bit register is not valid source operand for a "movl"
instruction, so the open64 compiler reports compile time error at -O0 (it works
fine at O1 and up).
Gcc compiles this test case without any complain, it does dead code elimination
at O0, so the offending code is NOT passed to code generation phase which
checks
the asmbly code constrains. Open64 does not perform this optimization at O0, so
it finds the constrain illegal.
We believe user should not depend on compiler optimizaiton removing illegal
code
to make it work, user is responsible for providing valid code to compiler, so
in
this case, I suggest to close the bug as user error.
(The work around is add a cast: "ir" ((int)stack_chk_guard), )
What do you think?
Thanks,
-Xiaohua
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