[PATCH] D71649: [PPC32] Emit R_PPC_PLTREL24 for calls to dso_local ifunc

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: PowerPC, hfinkel, nemanjai, jhibbits, sfertile, vit9696.
Herald added subscribers: llvm-commits, jsji, kbarton, hiraditya.
Herald added a project: LLVM.

  static void *ifunc(void) __attribute__((ifunc("resolver")));
  void foo() { ifunc(); }

The relocation produced by the ifunc() call:

1. gcc -msecure-plt -fPIC => R_PPC_PLTREL24 r_addend=0x8000
2. gcc -msecure-plt -PIE => R_PPC_PLTREL24 r_addend=0x8000
3. clang -msecure-plt -fPIC => R_PPC_PLTREL24 r_addend=0x8000
4. clang -msecure-plt -fPIE => R_PPC_REL24

4 is incorrect. The R_PPC_REL24 needs a call stub due to ifunc. If this
relocation is mixed with other R_PPC_PLTREL24(r_addend=0x8000) in a
function, both GNU ld and lld (after D71621 <https://reviews.llvm.org/D71621> fix) may produce a wrong
result.

This patch fixes 4 to use R_PPC_PLTREL24, which matches GCC.
Both GNU ld and lld (after D71621 <https://reviews.llvm.org/D71621>) will be happy.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71649

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/test/CodeGen/PowerPC/ifunc-dsolocal.ll


Index: llvm/test/CodeGen/PowerPC/ifunc-dsolocal.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/ifunc-dsolocal.ll
@@ -0,0 +1,19 @@
+; RUN: llc %s -o - -mtriple=powerpc | FileCheck --check-prefix=REL %s
+; RUN: llc %s -o - -mtriple=powerpc -relocation-model=pic | FileCheck --check-prefix=PLTREL %s
+; RUN: llc %s -o - -mtriple=powerpc64 | FileCheck --check-prefix=REL %s
+; RUN: llc %s -o - -mtriple=powerpc64 -relocation-model=pic | FileCheck --check-prefix=REL %s
+
+ at ifunc1 = dso_local ifunc void(), i8*()* @resolver
+ at ifunc2 = ifunc void(), i8*()* @resolver
+
+define i8* @resolver() { ret i8* null }
+
+define void @foo() {
+  ; REL: bl ifunc1{{$}}
+  ; REL: bl ifunc2{{$}}
+  ; PLTREL: bl ifunc1 at PLT
+  ; PLTREL: bl ifunc2 at PLT
+  call void @ifunc1()
+  call void @ifunc2()
+  ret void
+}
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -5102,9 +5102,10 @@
   auto isLocalCallee = [&]() {
     const GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
     const Module *Mod = DAG.getMachineFunction().getFunction().getParent();
+    const GlobalValue *GV = G ? G->getGlobal() : nullptr;
 
-    return DAG.getTarget().shouldAssumeDSOLocal(*Mod,
-                                                G ? G->getGlobal() : nullptr);
+    return DAG.getTarget().shouldAssumeDSOLocal(*Mod, GV) &&
+           !dyn_cast_or_null<GlobalIFunc>(GV);
   };
 
   bool UsePlt = Subtarget.is32BitELFABI() && !isLocalCallee();


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