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[PAC][ThinLTO] Fix auth key for GOT entries of function symbols #131467

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Merged
kovdan01 merged 4 commits into from
Apr 19, 2025
Merged

[PAC][ThinLTO] Fix auth key for GOT entries of function symbols #131467

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479f585
[PAC][ThinLTO] Fix auth key for GOT entries of function symbols
kovdan01 Mar 15, 2025
feab9b8
Merge branch 'main' into pauth-lto-signed-got-key-main
kovdan01 Apr 14, 2025
af42aeb
Enhance test
kovdan01 Apr 14, 2025
efaa9e2
Limit special behavior to AArch64
kovdan01 Apr 14, 2025
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7 changes: 7 additions & 0 deletions lld/ELF/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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38 changes: 38 additions & 0 deletions lld/test/ELF/lto/aarch64-pac-got-func.ll
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@@ -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"

@var = external global ptr

declare void @foo()

define void @bar() #0 {
entry:
store ptr ptrauth (ptr @foo, i32 0), ptr @var
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@MaskRay MaskRay Apr 8, 2025 •
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Perhaps rename var to something else then add

store ptr ptrauth (ptr @func, i32 0), ptr @g
store ptr ptrauth (ptr @func_undef, i32 0), ptr @g
store ptr ptrauth (ptr @var_undef, i32 0), ptr @g
store ptr ptrauth (ptr @var, i32 0), ptr @g

Use llvm.used so that the symbols will not be optimized out.

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@kovdan01 kovdan01 Apr 14, 2025

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Use llvm.used so that the symbols will not be optimized out.

Maybe I'm doing smth wrong, but it looks like that llvm.used has no effect and only the symbol from the last store operation is present in GOT. This is what I've added to the code (right before @bar definition, just in case):

@llvm.used = appending global [4 x ptr] [ ptr @func, ptr @func_undef, ptr @var, ptr @var_undef], section "llvm.metadata"

Adding @g to this array, removing section "llvm.metadata", moving this array definition to the end of the file does not change the behavior.

This smells like a bug, given llvm.used description from IR reference: https://llvm.org/docs/LangRef.html#the-llvm-used-global-variable.

@MaskRay does this look like a bug for you as well, or maybe I'm just mis-using this special array?

As for now, I've just used a separate global for each store - g1, g2, g3, g4. Not elegant, but at least it works :)

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}