[PATCH] gmp: compile with -DPIC to use correct asm code

[Felix Fietkau]

On 2021-03-12 11:34, Stijn Tintel wrote:
> On 11/03/2021 23:46, Eneas U de Queiroz wrote:
>> The library is always compiled with $(FPIC) (-fPIC or -fpic), even for
>> the static library.
>>
>> There are some assembly sources that decide whether or not to enable
>> PIC code by checking if PIC is defined.  It counts on libtool to define
>> it, but libtool does it only when producing code for the dynamic
>> library, while we need it for both.
>>
>> Ensure it is defined by adding it to CFLAGS next to $(FPIC).
>>
>> It avoids linking errors with strongswan on x86_64:
>>
>> ld: libgmp.a(bdiv_q_1.o): relocation R_X86_64_PC32 against symbol
>> `__gmp_binvert_limb_table' can not be used when making a shared object;
>> recompile with -fPIC
>>
>> Cc: Stijn Tintel <stijn at linux-ipv6.be>
>> Signed-off-by: Eneas U de Queiroz <cotequeiroz at gmail.com>
>> ---
>>
>> There's an error on one architecture, and all others work fine without
>> this, so I'm uneasy changing this and then breaking stuff that was
>> working fine otherwise.  However, it feels wrong to me to generate PIC
>> code from C files, but not use it in asm sources, which is essentially
>> what I am changing here.
>>
>> I've looked at asm sources for different chitectures, and there are
>> checks for PIC in: arm64, arm, x86_64, x86, and ppc asm sources, but the
>> error only appears on x86_64.
>>
>> For most CPUs, ifdef(`PIC'), is just used to do different definitions of
>> LEA (Load Effective Address).  However, both x86 and x86_64 have many
>> other checks.
>>
>> I've looked at bdiv_q_1.asm for different CPUs, and they all do some
>> form of LEA(binvert_limb_table), except for x86, where it will do it
>> only when PIC is defined.  That may explain why x86_64 is affected, and
>> x86 is not.
>>
>> I have not investigated further details.
>>
>> Alternatively, we can define it only for x86_64, which is where we know
>> there's a build failure with the linker asking to recompile with -fPIC.
>>
> I'm sorry, but I lack the knowledge to review this.

I think the patch makes sense and -DPIC should be used along with -fPIC.
I don't see any reason to make it x86_64 specific.

- Felix