Re: [Tinycc-devel] BUG: called function should pop the arguments when using fastcall

[张博洋]

Hello,

   I tested this on Linux myself, according to gcc doc, the behavior 
should be same as windows: 
https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html

> fastcall
>
>     On x86-32 targets, the fastcall attribute causes the compiler to pass the 
> first argument (if of integral type) in the register ECX and the second 
> argument (if of integral type) in the register EDX. Subsequent and other typed 
> arguments are passed on the stack. The called function pops the arguments off 
> the stack. If the number of arguments is variable all arguments are pushed on 
> the stack.

   I also tested with a simple C source code:
> int __attribute__ ((fastcall)) test(int a, int b, int c, int d, int e)
> {
>     return a - b + c + d + e;
> }
   GCC generated the following assembly:

> Disassembly of section .text:
>
> 00000000 <test>:
>    0:   55                      push   %ebp
>    1:   89 e5                   mov    %esp,%ebp
>    3:   83 ec 08                sub    $0x8,%esp
>    6:   89 4d fc                mov    %ecx,-0x4(%ebp)
>    9:   89 55 f8                mov    %edx,-0x8(%ebp)
>    c:   8b 45 f8                mov    -0x8(%ebp),%eax
>    f:   8b 55 fc                mov    -0x4(%ebp),%edx
>   12:   29 c2                   sub    %eax,%edx
>   14:   8b 45 08                mov    0x8(%ebp),%eax
>   17:   01 c2                   add    %eax,%edx
>   19:   8b 45 0c                mov    0xc(%ebp),%eax
>   1c:   01 c2                   add    %eax,%edx
>   1e:   8b 45 10                mov    0x10(%ebp),%eax
>   21:   01 d0                   add    %edx,%eax
>   23:	c9                   	leave  
>   24:	c2 0c 00             	ret    $0xc

  The "ret $0xc" indicates that the behavior is same as windows.



Zhang Boyang





在 2017年08月23日 20:42, grischka 写道:
> 张博洋 wrote:
> > Hello,
> >
> >   I found that TCC implement 'fastcall' that the calling function pops 
> > arguments. However, according to MSDN 
> > (https://msdn.microsoft.com/en-us/library/6xa169sk.aspx), the called 
> > function should pop arguments when using fastcall.
> >   I provided a patch and I have already pushed it to the mob branch, 
> > since I'm new to TCC and compilers, please review my patch carefully.
> >   I also wrote a test case which is in attachments, you may use the 
> > testcase to discover the problem.
>
> Did someone try this on Linux?  The wanted behavior might be different.
>
> -- gr
>
> >   Thanks
> >
> > Zhang Boyang
>
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