From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dibyendu Majumdar <mobile@majumdar.org.uk>
Subject: Re: Potential issue with handling of va_arg()
Date: Fri, 31 Mar 2017 15:34:24 +0100
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On 31 March 2017 at 15:06, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> On 31 March 2017 at 14:47, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
>> I am investigating a failure in this test:
>>
>> #include <stdarg.h>
>> #include <stdlib.h>
>> #include <stdio.h>
>>
>> void error_message(const char *fmt, ...) {
>> va_list argp;
>> va_start(argp, fmt);
>> vfprintf(stdout, fmt, argp);
>> va_end(argp);
>> }
>>
>> int main(void)
>> {
>> error_message("%s\n", "hello world");
>> return 0;
>> }
>>
>>
>> The linearized output for error_message() is:
>>
>> rror_message:
>> .L0:
>> <entry-point>
>> store.64    %arg1 -> 0[fmt]
>> cast.64     %r2 <- (64) fmt
>> load.64     %r3 <- 0[stdout]
>> call.32     %r6 <- vfprintf, %r3, %arg1, %r2
>> ret
>>
>> Above seems incorrect to me, as %r2 should be pointing to [8]fmt presumably?
>>
>
> I think this might be because the macro __builtin_va_start() is being
> defined in sparse but this doesn't match what gets defined by gcc? I
> see this in sparse:
>
> #define __builtin_va_start(a,b) ((a) = (__builtin_va_list)(&(b)))
>
> but if I run above code through gcc then preprocessed output says:
>
> __builtin_va_start(argp, fmt);
>

And it also seems that LLVM provides special instructions and
intrinsics for variable argument handling:

http://llvm.org/docs/LangRef.html#int-varargs

I don't know how to fix this issue as it appears that there is
OP_VAARG instruction in sparse but this is not implemented/output?

Thanks and Regards
Dibyendu