[lld] r351335 - [ELF][AArch64] Add R_AARCH64_PLT_PAGE_PC to isRelExpr

[Hans Wennborg via llvm-commits]

Merged to 8.0 in r351446.

On Wed, Jan 16, 2019 at 2:27 PM Peter Smith via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: psmith
> Date: Wed Jan 16 05:24:02 2019
> New Revision: 351335
>
> URL: http://llvm.org/viewvc/llvm-project?rev=351335&view=rev
> Log:
> [ELF][AArch64] Add R_AARCH64_PLT_PAGE_PC to isRelExpr
>
> As a follow on to D56666 (r351186) there is a case when taking the address
> of an ifunc when linking -pie that can generate a spurious can't create
> dynamic relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol in readonly
> segment. Specifically the case is where the ifunc is in the same
> translation unit as the address taker, so given -fpie the compiler knows
> the ifunc is defined in the executable so it can use a non-got-generating
> relocation.
>
> The error message is due to R_AARCH64_PLT_PAGE_PC not being added to
> isRelExpr, its non PLT equivalent R_AARCH64_PAGE_PC is already in
> isRelExpr.
>
> Differential Revision: https://reviews.llvm.org/D56724
>
>
> Added:
>     lld/trunk/test/ELF/aarch64-gnu-ifunc-address-pie.s
> Modified:
>     lld/trunk/ELF/Relocations.cpp
>
> Modified: lld/trunk/ELF/Relocations.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Relocations.cpp?rev=351335&r1=351334&r2=351335&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Relocations.cpp (original)
> +++ lld/trunk/ELF/Relocations.cpp Wed Jan 16 05:24:02 2019
> @@ -356,7 +356,7 @@ static bool needsGot(RelExpr Expr) {
>  static bool isRelExpr(RelExpr Expr) {
>    return isRelExprOneOf<R_PC, R_GOTREL, R_GOTREL_FROM_END, R_MIPS_GOTREL,
>                          R_PPC_CALL, R_PPC_CALL_PLT, R_AARCH64_PAGE_PC,
> -                        R_RELAX_GOT_PC>(Expr);
> +                        R_AARCH64_PLT_PAGE_PC, R_RELAX_GOT_PC>(Expr);
>  }
>
>  // Returns true if a given relocation can be computed at link-time.
>
> Added: lld/trunk/test/ELF/aarch64-gnu-ifunc-address-pie.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/aarch64-gnu-ifunc-address-pie.s?rev=351335&view=auto
> ==============================================================================
> --- lld/trunk/test/ELF/aarch64-gnu-ifunc-address-pie.s (added)
> +++ lld/trunk/test/ELF/aarch64-gnu-ifunc-address-pie.s Wed Jan 16 05:24:02 2019
> @@ -0,0 +1,44 @@
> +# REQUIRES: aarch64
> +# RUN: llvm-mc -filetype=obj -triple=aarch64-none-linux-gnu %s -o %t.o
> +# RUN: ld.lld -pie %t.o -o %tout
> +# RUN: llvm-objdump -D %tout | FileCheck %s
> +# RUN: llvm-readobj -r %tout | FileCheck %s -check-prefix=CHECK-RELOCS
> +
> +# Test that when we take the address of a preemptible ifunc using -fpie, we can
> +# handle the case when the ifunc is in the same translation unit as the address
> +# taker. In this case the compiler knows that ifunc is not defined in a shared
> +# library so it can use a non got generating relative reference.
> +.text
> +.globl myfunc
> +.type myfunc, at gnu_indirect_function
> +myfunc:
> + ret
> +
> +.text
> +.globl main
> +.type main, at function
> +main:
> + adrp x8, myfunc
> + add  x8, x8, :lo12: myfunc
> + ret
> +
> +# CHECK: 0000000000010000 myfunc:
> +# CHECK-NEXT:    10000:        c0 03 5f d6     ret
> +# CHECK: 0000000000010004 main:
> +# CHECK-NEXT:    10004:        08 00 00 90     adrp    x8, #0
> +# x8 = 0x10000
> +# CHECK-NEXT:    10008:        08 41 00 91     add     x8, x8, #16
> +# x8 = 0x10010 = .plt for myfunc
> +# CHECK-NEXT:    1000c:        c0 03 5f d6     ret
> +# CHECK-NEXT: Disassembly of section .plt:
> +# CHECK-NEXT: 0000000000010010 .plt:
> +# CHECK-NEXT:    10010:        90 00 00 90     adrp    x16, #65536
> +# CHECK-NEXT:    10014:        11 02 40 f9     ldr     x17, [x16]
> +# CHECK-NEXT:    10018:        10 02 00 91     add     x16, x16, #0
> +# CHECK-NEXT:    1001c:        20 02 1f d6     br      x17
> +
> +# CHECK-RELOCS: Relocations [
> +# CHECK-RELOCS-NEXT:   Section {{.*}} .rela.plt {
> +# CHECK-RELOCS-NEXT:     0x20000 R_AARCH64_IRELATIVE - 0x10000
> +# CHECK-RELOCS-NEXT:   }
> +# CHECK-RELOCS-NEXT: ]
>
>
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