[PATCH] PR ld/19636: pie changes program behavior and generate unnecessary dynamic symbols
H.J. Lu
hjl.tools@gmail.com
Sun Feb 21 05:59:00 GMT 2016
On Wed, Feb 17, 2016 at 10:31 PM, Alan Modra <amodra@gmail.com> wrote:
> On Wed, Feb 17, 2016 at 08:24:06PM -0800, H.J. Lu wrote:
>> On Wed, Feb 17, 2016 at 4:42 PM, Alan Modra <amodra@gmail.com> wrote:
>> > On Wed, Feb 17, 2016 at 03:33:51PM -0800, H.J. Lu wrote:
>> >> On Tue, Feb 16, 2016 at 9:23 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> >> > On Mon, Feb 15, 2016 at 07:00:32AM -0800, H.J. Lu wrote:
>> >> >> I fixed x86. Other backends need similar fix. Any comments?
>> >
>> > If you aren't going to fix other backends too, have you at least run
>> > the testsuite for all the other ELF targets that use SYMBOLIC_BIND?
>>
>> Should I enable them for all ELF target with PIE/PIC support?
>> All of them fail since none of them handle PIE correctly.
>
> No, I meant the existing testsuite, not your new tests. These changes
> are quite likely to break existing tests.
>
>> >> -/* Will a symbol be bound to the definition within the shared
>> >> - library, if any. A unique symbol can never be bound locally. */
>> >> -#define SYMBOLIC_BIND(INFO, H) \
>> >> - (!(H)->unique_global \
>> >> - && ((INFO)->symbolic || ((INFO)->dynamic && !(H)->dynamic)))
>> >> +/* Will a symbol be bound to the definition within the PIC object, if
>> >> + any. A unique symbol can never be bound locally. Symbols are always
>> >> + bound locally in PIE, similar to -shared -Bsymbolic. */
>> >> +#define SYMBOLIC_BIND(INFO, H) \
>> >> + (!(H)->unique_global \
>> >> + && ((INFO)->symbolic \
>> >> + || ((INFO)->dynamic && !(H)->dynamic) \
>> >> + || bfd_link_pie (INFO)))
>> >
>> > This probably should be bfd_link_executable rather than bfd_link_pie.
>>
>> SYMBOLIC_BIND was intended for shared library and is used only when
>> PIC is true. It is never applied to bfd_link_hash_undefweak. That is why
>> I added bfd_link_pie. Change it to bfd_link_executable is a good start if
>> we want to extend it to executable where bfd_link_hash_undefweak is a
>> special case. bfd_link_hash_undefweak always binds locally in executable
>> and never binds locally in shared library. Should we extend SYMBOLIC_BIND
>> to cover all cases so that we don't have check PIC nor undefweak before
>> using it?
>
> The reason I suggested bfd_link_executable was simply that it is a
> property of ELF executables in general that symbols bind locally, not
> just a property of PIEs. I wouldn't try to extend SYMBOLIC_BIND to
> other cases just yet, and your claim about bfd_link_hash_undefweak is
> not true. That was the whole point of my comment below.
I removed the SYMBOLIC_BIND change.
>> > This change is incorrect. Some targets (even x86_64 with -fPIC)
>> > support
>> > if (fun)
>> > fun ();
>> > for an undefined weak fun at link time, making fun dynamic and
>> > emitting dynamic relocs against fun. So when the executable is linked
>> > against a new shared library that provides fun, fun will be called.
>
>> Yes, it should be moved before
>
> No, that change should not be added at all!
I moved it to x86 backend via elf_backend_fixup_symbol.
>> It exposed more issues in x86 backends :-).
>
> I'm not surprised. :) I tried something similar many years ago, but
> ran into "issues" in the powerpc backends, and decided I didn't care
> enough about a few extra symbols.
>
Here is the final patch. There are some extra failures:
crisv32-linux:
New failures:
FAIL: ld-elf/pr19636-1d
FAIL: ld-elf/pr19636-1e
FAIL: ld-elf/pr19636-2a
frv-linux:
New failures:
FAIL: FRV uClinux PIC relocs to weak undefined symbols, pie linking
FAIL: ld-elf/pr19636-1d
FAIL: ld-elf/pr19636-1e
i370-linux:
New failures:
FAIL: ld-elf/pr19636-1d
FAIL: ld-elf/pr19636-1e
FAIL: ld-elf/pr19636-2b
FAIL: ld-elf/pr19636-2c
frv-elf:
New failures:
FAIL: FRV uClinux PIC relocs to weak undefined symbols, pie linking
They are due to the existing issues in those backends.
--
H.J.
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