[Bug target/50818] New: va_list is filled incorrectly in functions with ms_abi attribute on amd64

[andrey.sploshnov at kaspersky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50818

 Bug #: 50818
   Summary: va_list is filled incorrectly in functions with ms_abi
attribute on amd64
Classification: Unclassified
   Product: gcc
   Version: 4.4.5
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: andrey.splosh...@kaspersky.com


Created attachment 25567
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25567
preprocessed output

Compile the following testcase on x86_64-linux-gnu target:

void __attribute__((ms_abi)) callee (const char* fmt, ...)
{
__builtin_va_list ap;
__builtin_va_start (ap, fmt);

const char* p = __builtin_va_arg(ap, const char*);

va_end (ap);
}

void caller ()
{
const char* str = "arg";
test_proc1("a string: %s", str);
}

After I've built the code with default Debian/squeeze compiler (gcc (Debian
4.4.5-8) 4.4.5), I've got the following piece of code in callee:

   leaq  -32(%rbp), %rax
   movl  $8, (%rax)
   leaq  -32(%rbp), %rax
   movl  $48, 4(%rax)
   leaq  -32(%rbp), %rax
   leaq  24(%rbp), %rdx
   movq  %rdx, 8(%rax)

It seems to me, that va_list is filled incorrectly: pointer to the argument is
saved in overflow_arg_area, but gp_offset is set to 8 instead of 48 (according
to "System V ABI, AMD64 supplement"). So the following va_arg is trying to
extract the pointer from reg_save_area instead of overflow_arg_area.

[Bug target/50818] va_list is filled incorrectly in functions with ms_abi attribute on amd64

[andrey.sploshnov at kaspersky dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50818

--- Comment #1 from Andrey Sploshnov  
2011-10-21 09:16:32 UTC ---
Sorry, there is a typo in the caller() function, it should be:

const char* str = "arg";
callee("a string: %s", str);

test.ii contains a correct version of the case