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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lld

Author: Daniil Kovalev (kovdan01)

<details>
<summary>Changes</summary>

Symtab is first filled with the data from the bitcode file, and all 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.

---
Full diff: https://github.com/llvm/llvm-project/pull/131467.diff


2 Files Affected:

- (modified) lld/ELF/Driver.cpp (+7) 
- (added) lld/test/ELF/lto/aarch64-pac-got-func.ll (+38) 


``````````diff
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 18f9fed0d08e2..434f17786c861 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2618,6 +2618,13 @@ void LinkerDriver::compileBitcodeFiles(bool skipLinkedOutput) {
     auto *obj = cast<ObjFile<ELFT>>(file.get());
     obj->parse(/*ignoreComdats=*/true);
 
+    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..e42f78d30adba
--- /dev/null
+++ b/lld/test/ELF/lto/aarch64-pac-got-func.ll
@@ -0,0 +1,38 @@
+; 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 0x2a8 contains 2 entries:
+; CHECK-NEXT:     Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
+; CHECK-NEXT: 00000000000203d8  0000000100000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 foo + 0
+; CHECK-NEXT: 00000000000203e0  0000000200000412 R_AARCH64_AUTH_GLOB_DAT 0000000000000000 var + 0
+
+; CHECK:      Hex dump of section '.got':
+; CHECK-NEXT: 0x000203d8 00000000 00000080 00000000 000000a0
+;;                                      ^^ 0b10000000 bit 63 address diversity = true, bits 61..60 key = IA
+;;                                                        ^^ 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 var = external global ptr
+
+declare void @foo()
+
+define void @bar() #0 {
+entry:
+  store ptr ptrauth (ptr @foo, i32 0), ptr @var
+  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}

``````````

</details>


https://github.com/llvm/llvm-project/pull/131467