pushl computed immediate address on 2.8.1
H.J. Lu
hjl@lucon.org
Fri Jan 9 20:42:00 GMT 1998
>
>
> I was thinking this was a bug in the SCO x86 assembler becuase it worked
> under GAS for Linux. However, after some prodding form the egcs folks
> that really know PIC, I'm wondering if this is actually a construct that
> GAS should produce an error for becuase GCC shouldn't emit it.
>
> The problem is that
>
> pushl $.LC0@GOTOFF(%ebx)
>
> seems to assemble just like
>
> pushl $LC0
>
> so it ends up generating an push of an absolute address once the
> linker gets done with it.
>
> Does this sound right at all? Should GAS error on this?
>
>
> Here's a short "hello, world" in PIC to exercise the issue.
>
>
> Thanx,
>
> RJL
>
> .file "test.c"
> .section .rodata
> .LC0:
> .string "Hello, World\n"
>
> .text
> .align 4
> .globl main
> .type main,@function
> main:
> pushl %ebp
> movl %esp,%ebp
> pushl %ebx
> call .L2
> .L2:
> popl %ebx
> addl $_GLOBAL_OFFSET_TABLE_+[.-.L2],%ebx
>
> // This is the aproach that works, and is what GCC should emit.
> // registers
> leal .LC0@GOTOFF(%ebx),%eax
> pushl %eax
> call printf@PLT
>
> // This what GCC does emit, but seems to be nonsensical.
> // assembler.
> pushl $.LC0@GOTOFF(%ebx)
> call printf@PLT
>
Which gcc are you using? How did you get gcc to emit that?
I only can get my gcc to generate
leal .LC0@GOTOFF(%ebx),%eax
pushl %eax
call printf@PLT
I tried egcs 971215, egcs 1.0.1 and gcc 2.8.0 971225. They
are all the same.
H.J.
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