[PATCH v6] elf/x86-64: Subtract __ImageBase for R_AMD64_IMAGEBASE

[H.J. Lu]

On Fri, Mar 5, 2021 at 4:11 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Fri, Mar 05, 2021 at 10:26:35AM -0800, H.J. Lu wrote:
> > On Fri, Mar 5, 2021 at 5:57 AM Alan Modra <amodra@gmail.com> wrote:
> > > This doesn't look like the right place to set up a reference to
> > > __executable_start.  Doing so in a new check_relocs in pei-x86_64.c
> > > that tests for an ELF output would be better.  I'm not suggesting that
> > > you run over relocs looking for R_AMD64_IMAGEBASE, that could be done
> > > but seems unnecessary.
> >
> > check_relocs is too late.  We need to do it in load_symbols ().  Otherwise,
> > __executable_start won't be defined.  I added pex64_link_add_symbols to
> > do it.
>
> Ah, I was forgetting that check_relocs now runs much later.  Even so,
> I would have thought that the PROVIDE would define the symbol?  The
> question is academic, I'm happy with pex64_link_add_symbols.
>
> > Here is the v5 patch.  OK for master?
>
> OK with three further changes.
> 1) The R_AMD64_IMAGEBASE handling should to be inside the
>    output_bfd == NULL block.  It is wrong to apply the image base
>    adjustment to the section for relocatable linking.  Doing so would
>    effectively change the reloc addend.

Fixed.

> 2) I worry about the abort, which I think you might hit if trying to
>    link PE objects into a pie.  One possible fix would be to change
>    the bfd_link_pde in pex64_link_add_symbols to !bfd_link_relocatable.
>    That might just be sweeping a problem under the rug, so an
>    alternative fix would be to remove the abort and instead return
>    with bfd_reloc_dangerous.  Either fix is fine with me.

Changed to return bfd_reloc_dangerous.

> 3) No need to check for bfd_target_elf_flavour in set_output_arch.
>

The check is needed for

./ld-new -z norelro
-L/export/gnu/import/git/gitlab/x86-binutils/ld/testsuite/ld-elf  -T
pr21884.t -o tmpdir/dump tmpdir/pr21884a.o tmpdir/pr21884b.o
Executing on host: sh -c {./ld-new -z norelro
-L/export/gnu/import/git/gitlab/x86-binutils/ld/testsuite/ld-elf  -T
pr21884.t -o tmpdir/dump tmpdir/pr21884a.o tmpdir/pr21884b.o  2>&1}
/dev/null dump.tmp (timeout = 300)
spawn [open ...]^M
sh: line 1: 1894243 Segmentation fault      (core dumped) ./ld-new -z
norelro -L/export/gnu/import/git/gitlab/x86-binutils/ld/testsuite/ld-elf
-T pr21884.t -o tmpdir/dump tmpdir/pr21884a.o tmpdir/pr21884b.o 2>&1
failed with: <sh: line 1: 1894243 Segmentation fault      (core
dumped) ./ld-new -z norelro
-L/export/gnu/import/git/gitlab/x86-binutils/ld/testsuite/ld-elf -T
pr21884.t -o tmpdir/dump tmpdir/pr21884a.o tmpdir/pr21884b.o 2>&1>, no
expected output
FAIL: ld-elf/pr21884

This is the patch I am checking in.

Thanks.

-- 
H.J.
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