Re: Bug 84762 - GCC for PowerPC32 violates the SysV ABI spec for small struct returns

[Franz Sirl <Franz dot Sirl-kernel at lauterbach dot com>]

Am 2018-11-19 um 15:36 schrieb Lokesh Janghel:
> Hi Segher,
>
> I am building the GCC with the following configuration ( using gcc trunk ).
>   ../gcc/configure --target=powerpc-linux
> --prefix=/opt/buckeye/powerpc-linux --disable-shared --disable-threads
> --enable-languages=c --with-newlib
>
> And my assembly code (without optimization) is:
> $ cc1   -msvr4-struct-return test.c
> .LFB0:
>          stwu 1,-32(1)
> .LCFI0:
>          stw 31,28(1)
> .LCFI1:
>          mr 31,1
> .LCFI2:
>          lis 9,.LC0@ha
>          la 9,.LC0@l(9)
>          lhz 10,0(9)
>          lbz 9,2(9)
>          sth 10,11(31)
>          stb 9,13(31)
>          lhz 10,11(31)
>          lbz 9,13(31)
>          sth 10,8(31)
>          stb 9,10(31)
>          li 9,0
>          lbz 10,8(31)
>          rlwinm 10,10,0,24,31
>          slwi 10,10,16
>          rlwinm 9,9,0,16,7
>          or 9,9,10
>          lbz 10,9(31)
>          rlwinm 10,10,0,24,31
>          slwi 10,10,8
>          rlwinm 9,9,0,24,15
>          or 9,9,10
>           lbz 10,10(31)
>          rlwinm 10,10,0,24,31
>          rlwinm 9,9,0,0,23
>          or 9,9,10
>          mr 3,9
>          addi 11,31,32
>          lwz 31,-4(11)
> .LCFI3:
>          mr 1,11
> .LCFI4:
>          blr
>
>
> Assembly code (with optimization -O2) is:
> $ cc1   -msvr4-struct-return -O2 test.c
> .LFB0:
>          stwu 1,-32(1)
> .LCFI0:
>          lis 3,0x11
>          ori 3,3,0x2233
>          addi 1,1,32
> .LCFI1:
>          blr
>
> As you mentioned assembly code in the GCC Bugzilla, I am not able to
> reproduce the issue.
> Please let me know your options used to reproduce this issue.

Hi,

you already reproduced the issue, according to the ABI, the code should 
look like:

.LFB0:
        stwu 1,-32(1)
.LCFI0:
        lis 3,0x1122
        ori 3,3,0x3300
        addi 1,1,32
.LCFI1:
        blr

So the value being passed around should be left-aligned in the register.

> Sirl,
> If you got the patch for this issue or will look into the issue.

I have an unfinished patch, it misses commandline handling, testcases 
and some code comments. I've attached it.

It's unlikely I can continue to work on it anytime soon :-(.

Franz

Attachment: ppc-small-struct-return-svr4-std.diff
Description: Text document