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Re: [PATCH] aarch64: Check PIC instead of SHARED in start.S
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
--
H.J.