On Wed, Jan 26, 2011 at 10:42:41AM -0500, Nicolas Pitre wrote:
> On Wed, 26 Jan 2011, Dave Martin wrote:
> > Alternatively, I wonder .alt.smp.init could make weak references
> > instead of normal references: then if the referenced section is
> > discarded, the reference will revert to 0 and the fixup code can
> > ignore it (at the expense of wasting a bit of space in the fixup table
> > ... but it's no worse than the current situation). From
> > experimentation, it seems this doesn't work if the referenced symbol
> > is defined in the same file, since the linker resolves the reference
> > before discarding sections, but maybe there's a way around it...
>
> That's strange. How can the linker resolve the reference if the
> referenced symbol is not in the same section as the reference source?
> What happens when the final link completes?
$ cat t.s
.section ".exit.text", "ax", %progbits
mov r0, r0
a: mov r0, r0
.pushsection ".alt.smp.fixup", "a"
.weak a
.long a
mov r0, r1
.popsection
$ arm-linux-as -o t.o t.s
$ arm-linux-nm t.o
00000004 W a
$ arm-linux-objdump -Dr t.o
Disassembly of section .exit.text:
00000000 <a-0x4>:
0: e1a00000 nop (mov r0,r0)
00000004 <a>:
4: e1a00000 .word 0xe1a00000
Disassembly of section .alt.smp.fixup:
00000000 <.alt.smp.fixup>:
0: 00000000 .word 0x00000000
0: R_ARM_ABS32 a
4: e1a00001 mov r0, r1
which when linked with:
SECTIONS
{
.alt.smp.init : { *(.alt.smp.init) }
/DISCARD/ : { *(.exit.text) }
}
$ arm-linux-ld -T t.lds -r -o t.oo t.o
`a' referenced in section `.alt.smp.fixup' of t.o: defined in discarded section
`.exit.text' of t.o
So I don't think weak symbols work like we want them to.
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