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

["andrey.sploshnov at kaspersky dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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: unassigned@gcc.gnu.org
        ReportedBy: andrey.sploshnov@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.