[PATCH] D70406: Ignore R_MIPS_JALR relocations against non-function symbols

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This revision was automatically updated to reflect the committed changes.
Closed by commit rG5bab291b7bd0: Ignore R_MIPS_JALR relocations against non-function symbols (authored by Alex Richardson <Alexander.Richardson at cl.cam.ac.uk>).

Changed prior to commit:
  https://reviews.llvm.org/D70406?vs=230088&id=230238#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70406/new/

https://reviews.llvm.org/D70406

Files:
  lld/ELF/Arch/Mips.cpp
  lld/test/ELF/mips-jalr-non-functions.s


Index: lld/test/ELF/mips-jalr-non-functions.s
===================================================================
--- /dev/null
+++ lld/test/ELF/mips-jalr-non-functions.s
@@ -0,0 +1,53 @@
+# REQUIRES: mips
+## Check that we ignore R_MIPS_JALR relocations agains non-function symbols.
+## Older versions of clang were erroneously generating them for function pointers
+## loaded from any table (not just the GOT) as well as against TLS function
+## pointers (when using the local-dynamic model), so we need to ignore these
+## relocations to avoid generating binaries that crash when executed.
+
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-linux %s -o %t.o
+# RUN: ld.lld -shared %t.o -o %t.so 2>&1 | FileCheck %s -check-prefix WARNING-MESSAGE
+# RUN: llvm-objdump --no-show-raw-insn --no-leading-addr -d %t.so | FileCheck %s
+
+.set	noreorder
+test:
+  .reloc .Ltmp1, R_MIPS_JALR, tls_obj
+.Ltmp1:
+  jr  $t9
+  nop
+# WARNING-MESSAGE: warning: found R_MIPS_JALR relocation against non-function symbol tls_obj. This is invalid and most likely a compiler bug.
+
+  .reloc .Ltmp2, R_MIPS_JALR, reg_obj
+.Ltmp2:
+  jr  $t9
+  nop
+# WARNING-MESSAGE: warning: found R_MIPS_JALR relocation against non-function symbol reg_obj. This is invalid and most likely a compiler bug.
+
+  .reloc .Ltmp3, R_MIPS_JALR, untyped
+.Ltmp3:
+  jr  $t9
+  nop
+
+## However, we do perform the optimization for untyped symbols:
+untyped:
+  nop
+
+  .type  tls_obj, at object
+  .section  .tbss,"awT", at nobits
+tls_obj:
+  .word 0
+
+  .type  reg_obj, at object
+  .data
+reg_obj:
+  .word 0
+
+# CHECK-LABEL: Disassembly of section .text:
+# CHECK-EMPTY:
+# CHECK-NEXT: test:
+# CHECK-NEXT: jr	$25
+# CHECK-NEXT: nop
+# CHECK-NEXT: jr	$25
+# CHECK-NEXT: nop
+# CHECK-NEXT: b	8 <untyped>
+# CHECK-NEXT: nop
Index: lld/ELF/Arch/Mips.cpp
===================================================================
--- lld/ELF/Arch/Mips.cpp
+++ lld/ELF/Arch/Mips.cpp
@@ -83,6 +83,17 @@
 
   switch (type) {
   case R_MIPS_JALR:
+    // Older versions of clang would erroneously emit this relocation not only
+    // against functions (loaded from the GOT) but also against data symbols
+    // (e.g. a table of function pointers). When we encounter this, ignore the
+    // relocation and emit a warning instead.
+    if (!s.isFunc() && s.type != STT_NOTYPE) {
+      warn(getErrorLocation(loc) +
+           "found R_MIPS_JALR relocation against non-function symbol " +
+           toString(s) + ". This is invalid and most likely a compiler bug.");
+      return R_NONE;
+    }
+
     // If the target symbol is not preemptible and is not microMIPS,
     // it might be possible to replace jalr/jr instruction by bal/b.
     // It depends on the target symbol's offset.


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