[lld] 8fdebff - [PAC][ThinLTO] Fix auth key for GOT entries of function symbols (#131467)

[via llvm-commits]

Author: Daniil Kovalev
Date: 2025-04-19T17:40:50+03:00
New Revision: 8fdebff69d92fd3c6023bf2d0646ca909bb4ec05

URL: https://github.com/llvm/llvm-project/commit/8fdebff69d92fd3c6023bf2d0646ca909bb4ec05
DIFF: https://github.com/llvm/llvm-project/commit/8fdebff69d92fd3c6023bf2d0646ca909bb4ec05.diff

LOG: [PAC][ThinLTO] Fix auth key for GOT entries of function symbols (#131467)

Symtab is first filled with the data from the bitcode file, and all
undefined symbols except TLS ones are `STT_NOTYPE`. Since auth key for a
signed GOT entry depends on the symbol type being `STT_FUNC` or not, we
need to update the symtab after the bitcode is compiled to an ELF object
and update symbol types for function symbols. This patch implements the
described behavior.

Added: 
    lld/test/ELF/lto/aarch64-pac-got-func.ll

Modified: 
    lld/ELF/Driver.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index b3c5518b42877..9d36071e1532f 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2638,6 +2638,18 @@ void LinkerDriver::compileBitcodeFiles(bool skipLinkedOutput) {
     auto *obj = cast<ObjFile<ELFT>>(file.get());
     obj->parse(/*ignoreComdats=*/true);
 
+    // This is only needed for AArch64 PAuth to set correct key in AUTH GOT
+    // entry based on symbol type (STT_FUNC or not).
+    // TODO: check if PAuth is actually used.
+    if (ctx.arg.emachine == EM_AARCH64) {
+      for (typename ELFT::Sym elfSym : obj->template getGlobalELFSyms<ELFT>()) {
+        StringRef elfSymName = check(elfSym.getName(obj->getStringTable()));
+        if (Symbol *sym = ctx.symtab->find(elfSymName))
+          if (sym->type == STT_NOTYPE)
+            sym->type = elfSym.getType();
+      }
+    }
+
     // For defined symbols in non-relocatable output,
     // compute isExported and parse '@'.
     if (!ctx.arg.relocatable)

diff  --git a/lld/test/ELF/lto/aarch64-pac-got-func.ll b/lld/test/ELF/lto/aarch64-pac-got-func.ll
new file mode 100644
index 0000000000000..a37c67a2f3ba8
--- /dev/null
+++ b/lld/test/ELF/lto/aarch64-pac-got-func.ll
@@ -0,0 +1,66 @@
+; REQUIRES: aarch64
+
+; RUN: llvm-as %s -o %t.o
+; RUN: ld.lld %t.o -shared -o %t
+; RUN: llvm-readelf -r -x.got %t | FileCheck %s
+
+; CHECK:      Relocation section '.rela.dyn' at offset 0x3d0 contains 8 entries:
+; CHECK-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+; CHECK-NEXT: 00000000000206a0  0000000100000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 func_undef + 0
+; CHECK-NEXT: 00000000000206a8  0000000200000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g1 + 0
+; CHECK-NEXT: 00000000000206b0  0000000300000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g2 + 0
+; CHECK-NEXT: 00000000000206b8  0000000400000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g3 + 0
+; CHECK-NEXT: 00000000000206c0  0000000500000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 g4 + 0
+; CHECK-NEXT: 00000000000206c8  0000000600000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 var_undef + 0
+; CHECK-NEXT: 0000000000020690  0000000700000412 R_AARCH64_AUTH_GLOB_DAT 0000000000010490 func + 0
+; CHECK-NEXT: 0000000000020698  0000000a00000412 R_AARCH64_AUTH_GLOB_DAT 00000000000306d0 var + 0
+
+; CHECK:      Hex dump of section '.got':
+; CHECK-NEXT: 0x00020690 00000000 00000080 00000000 000000a0
+;;                                      ^^ func: 0b10000000 bit 63 address diversity = true, bits 61..60 key = IA
+;;                                                        ^^ var: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+; CHECK-NEXT: 0x000206a0 00000000 00000080 00000000 000000a0
+;;                                      ^^ func_undef: 0b10000000 bit 63 address diversity = true, bits 61..60 key = IA
+;;                                                        ^^ g1: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+; CHECK-NEXT: 0x000206b0 00000000 000000a0 00000000 000000a0
+;;                                      ^^ g2: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+;;                                                        ^^ g3: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+; CHECK-NEXT: 0x000206c0 00000000 000000a0 00000000 000000a0
+;;                                      ^^ g4: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+;;                                                        ^^ var_undef: 0b10100000 bit 63 address diversity = true, bits 61..60 key = DA
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+ at g1 = external global ptr
+ at g2 = external global ptr
+ at g3 = external global ptr
+ at g4 = external global ptr
+
+define void @func() {
+entry:
+  ret void
+}
+declare void @func_undef()
+
+ at var = global i32 42
+ at var_undef = external global i32
+
+define void @bar() #0 {
+entry:
+  store ptr ptrauth (ptr @func, i32 0), ptr @g1
+  store ptr ptrauth (ptr @func_undef, i32 0), ptr @g2
+  store ptr ptrauth (ptr @var, i32 0), ptr @g3
+  store ptr ptrauth (ptr @var_undef, i32 0), ptr @g4
+  ret void
+}
+
+define void @_start() {
+entry:
+  ret void
+}
+
+attributes #0 = {"target-features"="+pauth"}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 8, !"ptrauth-elf-got", i32 1}