[PATCH] D56724: [LLD][ELF][AArch64] Add R_AARCH64_PLT_PAGE_PC to isRelExpr

[Peter Smith via Phabricator via llvm-commits]

peter.smith created this revision.
peter.smith added reviewers: ruiu, grimar.
Herald added subscribers: kristof.beyls, arichardson, javed.absar, emaste.
Herald added a reviewer: espindola.

As a follow on to D56666 <https://reviews.llvm.org/D56666> (r351186) there is a case when taking the address of an ifunc when compiling -fpie and 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 that the ifunc is going to be 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. I've checked that the output is comparable to ld.bfd and ld.gold.

I found this while checking combinations of compilation and link options involving taking the address of an ifunc; for ld.gold, ld.bfd and ld.lld.


https://reviews.llvm.org/D56724

Files:
  ELF/Relocations.cpp
  test/ELF/aarch64-gnu-ifunc-address-pie.s


Index: test/ELF/aarch64-gnu-ifunc-address-pie.s
===================================================================
--- /dev/null
+++ test/ELF/aarch64-gnu-ifunc-address-pie.s
@@ -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: ]
Index: ELF/Relocations.cpp
===================================================================
--- ELF/Relocations.cpp
+++ ELF/Relocations.cpp
@@ -356,7 +356,7 @@
 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.


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