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Re: [PATCH] aarch64: Check PIC instead of SHARED in start.S
On 06/10/17 13:34, H.J. Lu wrote:
> On 10/6/17, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>> On 03/10/17 16:31, Szabolcs Nagy wrote:
>>> On 03/10/17 11:39, Szabolcs Nagy wrote:
>>>> On 02/10/17 12:20, H.J. Lu wrote:
>>>>> On 10/2/17, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>>>>>> On 29/09/17 22:32, H.J. Lu wrote:
>>>>>>> Since start.o may be compiled as PIC, we should check PIC instead of
>>>>>>> SHARED.
>>>>>>>
>>>>>>> OK for master?
>>>>>>>
>>>>>>
>>>>>> i believe that the compile/link tests worked..
>>>>>
>>>>> Does static PIE of hjl/pie/static branch run on arm and aarch64?
>>>>>
>>>>
>>>> no, if i build with --enable-static-pie the install step
>>>> fails when the static linked sln runs.
>>>>
>>>> there are relative relocs against the func ptrs that are
>>>> loaded from GOT in the startup code, but execution fails
>>>> even before those are used because there are R*_JUMP_SLOT
>>>> and R*_GLOB_DAT relocs which are not processed correctly.
>>>>
>>>> in particular in
>>>> if (__pthread_initialize_minimal != NULL)
>>>> __pthread_initialize_minimal ();
>>>> the symbol value loaded from GOT is non-NULL even though
>>>> there is no pthread linked in, that is probably a linker bug.
>>>>
>>>
>>> it seems weak extern symbol is accessed via got and at
>>> link time that is not relaxed to 0 with -static -pie
>>> and the got entry is not initialized to 0 either.
>>
>> aarch64 dl-machine.h has
>>
>> struct link_map *sym_map = RESOLVE_MAP (&sym, version, r_type);
>> ElfW(Addr) value = sym_map == NULL ? 0 : sym_map->l_addr +
>> sym->st_value;
>>
>> x86_64 has
>>
>> struct link_map *sym_map = RESOLVE_MAP (&sym, version, r_type);
>> ElfW(Addr) value = (sym == NULL ? 0
>> : (ElfW(Addr)) sym_map->l_addr + sym->st_value);
>>
>> sym_map is always == BOOTSTRAP_MAP in case of static pie, so
>> tye sym_map == NULL check is not true on aarch64 case for weak
>> undef symbols.
>>
>> so either targets need to be fixed to not use sym_map check
>> for detecting undef weak (powerpc32, powerpc64, aarch64,
>> i386, arm, sh, sparc32, sparc64) or RESOLVE_MAP should not
>> be unconditionally set to BOOTSTRAP_MAP in _dl_relocate_static_pie
>> (since that is not true for undef symbols)
>>
>
> It shouldn't matter. All undefined weak symbols should be resolved
> to 0 in static PIE by linker. See:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=22269
>
ok, thanks for the bug report, but i prefer to also
fix the dynamic linker to try set abs/got/jumpslot
relocs for weak undef syms to 0, so it can work with
earlier binutils.