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Date: Sun, 19 Oct 2014 22:29:35 +0200
From: Felix Janda <felix.janda@...teo.de>
To: musl@...ts.openwall.com
Subject: Re: debugging problem with musl ld and qemu-ppc
Felix Janda wrote:
> Rich Felker wrote:
[..]
> > What I'm not clear about is the cause for why the linker is forcing
> > you back to the bss-plt model. It might be a matter of the strange
> > relocation type you put in a.s:
> >
> > 00000000 <.text>:
> > 0: 48 00 00 00 b 0x0
> > 0: R_PPC_LOCAL24PC _GLOBAL_OFFSET_TABLE_
>
> The problem caused a self-compiled native gcc to crash because the file
> "mpn/powerpc32/elf.m4" (used to generate some assembly) in the gmp tree
> contains a similar instruction.
>
> I've found the part in binutils emitting the warning and will try to see
> why it forces bss-plt.
This seems to be caused by the part starting from lines 4267 in [1]
/* This refers only to functions defined in the shared library. */
case R_PPC_LOCAL24PC:
if (h != NULL && h == htab->elf.hgot && htab->plt_type == PLT_UNSET)
{
htab->plt_type = PLT_OLD;
htab->old_bfd = abfd;
}
I think it was added to be helpful and detect the construction
bl _GLOBAL_OFFSET_TABLE_@...al-4
mflr r30
intended to load a pointer to the got into r30, which no longer works
with secure-plt. See [2].
Felix
[1]: http://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf32-ppc.c;h=04c2d6ad60b4122eb1727e932cfcda035feeac68;hb=HEAD
[2]: http://www.sourceware.org/ml/binutils/2005-05/txt00011.txt
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