-mlong-calls generates non-PIC code on ARM

[glandium]

Bugzilla Link	40624
Version	unspecified
OS	Linux
CC	@froydnj

Extended Description

With the following source:

extern __attribute__((visibility("hidden"))) int foo();

int bar() { return foo(); };

clang generates the following with -fPIC -mlong-calls -O3 --target=armv7a-linux-gnueabi:

bar:
        ldr     r0, .LCPI0_0
        bx      r0
.LCPI0_0:
        .long   foo

That is not PIC, as that .LCPI0_0 label is in .text.

GCC generates the following:

bar:
        ldr     r3, .L3
.LPIC0:
        add     r3, pc, r3
        bx      r3
.L3:
        .word   foo-(.LPIC0+8)

(All courtesy of godbolt)

https://godbolt.org/z/gKwbiO

[llvmbot]

@llvm/issue-subscribers-backend-arm

Author: Mike Hommey (glandium)

| | | | --- | --- | | Bugzilla Link | [40624](https://llvm.org/bz40624) | | Version | unspecified | | OS | Linux | | CC | @froydnj |

Extended Description

With the following source:

extern __attribute__((visibility("hidden"))) int foo();

int bar() { return foo(); };

clang generates the following with -fPIC -mlong-calls -O3 --target=armv7a-linux-gnueabi:

bar:
        ldr     r0, .LCPI0_0
        bx      r0
.LCPI0_0:
        .long   foo

That is not PIC, as that .LCPI0_0 label is in .text.

GCC generates the following:

bar:
        ldr     r3, .L3
.LPIC0:
        add     r3, pc, r3
        bx      r3
.L3:
        .word   foo-(.LPIC0+8)

(All courtesy of godbolt)

https://godbolt.org/z/gKwbiO

[hstk30-hw]

So, can I say -mlong-calls isn't currently compatible with position independent code in LLVM?

GCC seem ok, GCC will generate R_ARM_GOT_BREL or R_ARM_REL32 for some call.
I'm not sure which behavior is reasonable.