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transform (gc): create stack slots in callers of external functions

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This updates the stack slot pass to include callers of external functions which may access non-argument memory.
Wiithout this change, a use-after-free could occur on WASM when calling a reentrant function or switching to another goroutine.
This commit is contained in:
Nia Waldvogel
2025-12-09 13:18:42 -05:00
committed by Ron Evans
parent ee0a10ec51
commit b37535bcfb
3 changed files with 154 additions and 32 deletions
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transform/testdata/gc-stackslots.ll
Vendored
+49
View File
@@ -4,6 +4,7 @@ target triple = "wasm32-unknown-unknown-wasm"
@runtime.stackChainStart = external global ptr
@someGlobal = global i8 3
@ptrGlobal = global ptr null
@arrGlobal = global [8 x i8] zeroinitializer
declare void @runtime.trackPointer(ptr nocapture readonly)
@@ -116,3 +117,51 @@ define void @allocAndSave(ptr %x) {
store ptr %x, ptr @ptrGlobal
ret void
}
declare void @"(internal/task).Pause"()
define ptr @getAndPause() {
%ptr = call ptr @getPointer()
call void @runtime.trackPointer(ptr %ptr)
; Calling a function with unknown memory access forces stack slot creation.
call void @"(internal/task).Pause"()
ret ptr %ptr
}
; Function Attrs: memory(readwrite)
declare void @externCallWithMemAttr() #0
define ptr @getAndCallWithMemAttr() {
%ptr = call ptr @getPointer()
call void @runtime.trackPointer(ptr %ptr)
; Calling an external function which may access non-arg memory forces stack slot creation.
call void @externCallWithMemAttr()
ret ptr %ptr
}
; Generic function that returns a slice (that must be tracked).
define {ptr, i32, i32} @getSlice() {
ret {ptr, i32, i32} {ptr @someGlobal, i32 8, i32 8}
}
define i32 @copyToSlice(ptr %src.ptr, i32 %src.len, i32 %src.cap) {
%dst = call {ptr, i32, i32} @getSlice()
%dst.ptr = extractvalue {ptr, i32, i32} %dst, 0
call void @runtime.trackPointer(ptr %dst.ptr)
%dst.len = extractvalue {ptr, i32, i32} %dst, 1
; Math intrinsics do not need stack slots.
%minLen = call i32 @llvm.umin.i32(i32 %dst.len, i32 %src.len)
; Intrinsics which only access argument memory do not need stack slots.
call void @llvm.memmove.p0.p0.i32(ptr %dst.ptr, ptr %src.ptr, i32 %minLen, i1 false)
ret i32 %minLen
}
; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare i32 @llvm.umin.i32(i32, i32) #1
; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
declare void @llvm.memmove.p0.p0.i32(ptr nocapture writeonly, ptr nocapture readonly, i32, i1 immarg) #2
attributes #0 = { memory(readwrite) }
attributes #1 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
attributes #2 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
transform/testdata/gc-stackslots.out.ll
Vendored
+59
View File
@@ -4,6 +4,7 @@ target triple = "wasm32-unknown-unknown-wasm"
@runtime.stackChainStart = internal global ptr null
@someGlobal = global i8 3
@ptrGlobal = global ptr null
@arrGlobal = global [8 x i8] zeroinitializer
declare void @runtime.trackPointer(ptr nocapture readonly)
@@ -166,3 +167,61 @@ define void @allocAndSave(ptr %x) {
store ptr %1, ptr @runtime.stackChainStart, align 4
ret void
}
declare void @"(internal/task).Pause"()
define ptr @getAndPause() {
%gc.stackobject = alloca { ptr, i32, ptr }, align 8
store { ptr, i32, ptr } { ptr null, i32 1, ptr null }, ptr %gc.stackobject, align 4
%1 = load ptr, ptr @runtime.stackChainStart, align 4
%2 = getelementptr { ptr, i32, ptr }, ptr %gc.stackobject, i32 0, i32 0
store ptr %1, ptr %2, align 4
store ptr %gc.stackobject, ptr @runtime.stackChainStart, align 4
%ptr = call ptr @getPointer()
%3 = getelementptr { ptr, i32, ptr }, ptr %gc.stackobject, i32 0, i32 2
store ptr %ptr, ptr %3, align 4
call void @"(internal/task).Pause"()
store ptr %1, ptr @runtime.stackChainStart, align 4
ret ptr %ptr
}
; Function Attrs: memory(readwrite)
declare void @externCallWithMemAttr() #0
define ptr @getAndCallWithMemAttr() {
%gc.stackobject = alloca { ptr, i32, ptr }, align 8
store { ptr, i32, ptr } { ptr null, i32 1, ptr null }, ptr %gc.stackobject, align 4
%1 = load ptr, ptr @runtime.stackChainStart, align 4
%2 = getelementptr { ptr, i32, ptr }, ptr %gc.stackobject, i32 0, i32 0
store ptr %1, ptr %2, align 4
store ptr %gc.stackobject, ptr @runtime.stackChainStart, align 4
%ptr = call ptr @getPointer()
%3 = getelementptr { ptr, i32, ptr }, ptr %gc.stackobject, i32 0, i32 2
store ptr %ptr, ptr %3, align 4
call void @externCallWithMemAttr()
store ptr %1, ptr @runtime.stackChainStart, align 4
ret ptr %ptr
}
define { ptr, i32, i32 } @getSlice() {
ret { ptr, i32, i32 } { ptr @someGlobal, i32 8, i32 8 }
}
define i32 @copyToSlice(ptr %src.ptr, i32 %src.len, i32 %src.cap) {
%dst = call { ptr, i32, i32 } @getSlice()
%dst.ptr = extractvalue { ptr, i32, i32 } %dst, 0
%dst.len = extractvalue { ptr, i32, i32 } %dst, 1
%minLen = call i32 @llvm.umin.i32(i32 %dst.len, i32 %src.len)
call void @llvm.memmove.p0.p0.i32(ptr %dst.ptr, ptr %src.ptr, i32 %minLen, i1 false)
ret i32 %minLen
}
; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare i32 @llvm.umin.i32(i32, i32) #1
; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
declare void @llvm.memmove.p0.p0.i32(ptr nocapture writeonly, ptr nocapture readonly, i32, i1 immarg) #2
attributes #0 = { memory(readwrite) }
attributes #1 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
attributes #2 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }