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

[Philip Prindeville]

> On Mar 12, 2021, at 6:25 AM, Felix Fietkau <nbd at nbd.name> wrote:
> 
> 
> 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


Maybe I'm missing something, but why not just fix rules.mk:


ifneq (,$(findstring $(ARCH) , aarch64 aarch64_be powerpc ))
  FPIC:=-fPIC
else
  FPIC:=-fpic
endif

HOST_FPIC:=-fPIC


To have the FPIC and HOST_FPIC definitions include -DPIC?