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[CrossDSO CFI] Make sure __cfi_check has BTI attribute. #131224

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[CrossDSO CFI] Make sure __cfi_check has BTI attribute. #131224

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cbdee73
[CrossDSO CFI] Make sure __cfi_check has BTI attribute.
efriedma-quic Mar 13, 2025
256aeb1
Use createWithDefaultAttr instead of explicitly modifying attributes.
efriedma-quic Mar 14, 2025
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24 changes: 18 additions & 6 deletions llvm/lib/Transforms/IPO/CrossDSOCFI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -82,14 +82,26 @@ void CrossDSOCFI::buildCFICheck(Module &M) {
}

LLVMContext &Ctx = M.getContext();
FunctionCallee C = M.getOrInsertFunction(
"__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
PointerType::getUnqual(Ctx), PointerType::getUnqual(Ctx));
FunctionType *CFICheckTy =
FunctionType::get(Type::getVoidTy(Ctx),
{Type::getInt64Ty(Ctx), PointerType::getUnqual(Ctx),
PointerType::getUnqual(Ctx)},
false);
FunctionCallee C = Function::createWithDefaultAttr(
CFICheckTy, GlobalValue::ExternalLinkage, 0, "__cfi_check", &M);
Function *F = cast<Function>(C.getCallee());
// Take over the existing function. The frontend emits a weak stub so that the
// linker knows about the symbol; this pass replaces the function body.
F->deleteBody();
F->setAlignment(Align(4096));
if (F->getName() != "__cfi_check") {
// The frontend might have already created a function named __cfi_check;
// delete it.
GlobalValue *G = M.getNamedValue("__cfi_check");
assert(G && "cfi_check must exist after we constructed it");
if (G->getAddressSpace() != F->getAddressSpace())
report_fatal_error("__cfi_check with unexpected address space");
G->replaceAllUsesWith(F);
F->takeName(G);
G->eraseFromParent();
}

Triple T(M.getTargetTriple());
if (T.isARM() || T.isThumb())
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53 changes: 53 additions & 0 deletions llvm/test/Transforms/CrossDSOCFI/aarch64-bti.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,53 @@
; RUN: opt -S -passes=cross-dso-cfi < %s | FileCheck %s

; CHECK: define void @__cfi_check({{.*}}) [[ATTR:#[0-9]+]] align 4096
; CHECK: [[ATTR]] = { "branch-target-enforcement" }

target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "aarch64-unknown-linux-gnu"

@_ZTV1A = constant i8 0, !type !4, !type !5
@_ZTV1B = constant i8 0, !type !4, !type !5, !type !6, !type !7

define signext i8 @f11() "branch-target-enforcement" !type !0 !type !1 {
entry:
ret i8 1
}

define signext i8 @f12() "branch-target-enforcement" !type !0 !type !1 {
entry:
ret i8 2
}

define signext i8 @f13() "branch-target-enforcement" !type !0 !type !1 {
entry:
ret i8 3
}

define i32 @f21() "branch-target-enforcement" !type !2 !type !3 {
entry:
ret i32 4
}

define i32 @f22() "branch-target-enforcement" !type !2 !type !3 {
entry:
ret i32 5
}

define weak_odr hidden void @__cfi_check_fail(ptr, ptr) "branch-target-enforcement" {
entry:
ret void
}

!llvm.module.flags = !{!8, !9}

!0 = !{i64 0, !"_ZTSFcvE"}
!1 = !{i64 0, i64 111}
!2 = !{i64 0, !"_ZTSFivE"}
!3 = !{i64 0, i64 222}
!4 = !{i64 16, !"_ZTS1A"}
!5 = !{i64 16, i64 333}
!6 = !{i64 16, !"_ZTS1B"}
!7 = !{i64 16, i64 444}
!8 = !{i32 4, !"Cross-DSO CFI", i32 1}
!9 = !{i32 8, !"branch-target-enforcement", i32 1}