Re: Fix Thumb-2 shared libraries

[Christophe LYON <christophe dot lyon at st dot com>]

On 25.08.2009 20:51, Daniel Jacobowitz wrote:
 > Unfortunately, this patch breaks Thumb-2 shared libraries.
Would you mind giving an example?

> But now the symbol table still points to the Thumb code, and we've
> marked the entry as STT_FUNC.  It ends up without the ISA bit set.
> This causes R_ARM_JUMP_SLOT relocations to jump to the target function
> as if it were ARM code - does not work.
I expected this part of allocate_dynrelocs() to be used only by
CALL-like relocs, and thought it was better to fix the definition in one
place, rather than several uses, which is error prone.

> If I revert just this part of your patch, there is one additional
> failure in the testsuite (thanks, as usual, for test cases!).  We use
> blx to branch to the PLT entry, so I assume that's what this hunk was
> for.  We have to change the use of the symbol in this case, rather
> than the definition.
Agreed.

> The test still needs a fixup, because the version that's there now
> would not work at runtime.  It has:
>
> .* <__lib_func3_from_thumb>:
>  .*:    e59fc000        ldr     ip, \[pc, #0\]  ; 1000364 <__lib_func3_from_thumb\+0x8>
>  .*:    e08ff00c        add     pc, pc, ip
>  .*:    feffff90        .word   0xfeffff90
>
> That will branch to lib_func3 in ARM mode, but lib_func3 is a Thumb
> function.

Good catch! Sorry not to have noticed this, despite having re-read my
patch quite a few times before committing!

> Here's a patch I'm testing for this failure.
It seems OK, but I think you forgot to add a test case :-)


Christophe.