[lld][WebAssembly] Fix SEGFAULT when importing wrapped symbol #169656
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When wrapping a symbol `foo`, we create the symbol `__wrap_foo` that replaces all mentions of `foo`. This change adds the correct signature to the wrapped symbol to enable generating an import for it.
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@llvm/pr-subscribers-lld-wasm Author: Lukas Döllerer (Lukasdoe) ChangesWhen wrapping a symbol So far, no valid signature has been attached to the undefined symbol, leading to a nullptr dereference in the logic for creating the import section. This change adds the correct signature to the wrapped symbol, enabling the generation of an import for it. Full diff: https://github.com/llvm/llvm-project/pull/169656.diff 3 Files Affected:
diff --git a/lld/test/wasm/wrap_import.s b/lld/test/wasm/wrap_import.s
new file mode 100644
index 0000000000000..526c1f539a4fd
--- /dev/null
+++ b/lld/test/wasm/wrap_import.s
@@ -0,0 +1,36 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
+# RUN: wasm-ld -emit-relocs -wrap nosuchsym -wrap foo -allow-undefined -o %t.wasm %t.o
+# RUN: obj2yaml %t.wasm | FileCheck %s
+
+.globl foo
+.globl _start
+
+foo:
+ .functype foo () -> (i32)
+ i32.const 1
+ end_function
+
+_start:
+ .functype _start () -> ()
+ call foo
+ drop
+ end_function
+
+# CHECK: - Type: IMPORT
+# CHECK-NEXT: Imports:
+# CHECK-NEXT: - Module: env
+# CHECK-NEXT: Field: __wrap_foo
+# CHECK-NEXT: Kind: FUNCTION
+# CHECK-NEXT SigIndex: 0
+
+# CHECK: - Type: CODE
+# CHECK-NEXT: Relocations:
+# CHECK-NEXT: - Type: R_WASM_FUNCTION_INDEX_LEB
+# CHECK-NEXT: Index: 1
+# CHECK-NEXT: Offset: 0x4
+
+# CHECK: FunctionNames:
+# CHECK-NEXT: - Index: 0
+# CHECK-NEXT: Name: __wrap_foo
+# CHECK-NEXT: - Index: 1
+# CHECK-NEXT: Name: _start
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index fac166587cb9b..97e50783985a8 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -1173,9 +1173,10 @@ struct WrappedSymbol {
Symbol *wrap;
};
-static Symbol *addUndefined(StringRef name) {
+static Symbol *addUndefined(StringRef name,
+ const WasmSignature *signature = nullptr) {
return symtab->addUndefinedFunction(name, std::nullopt, std::nullopt,
- WASM_SYMBOL_UNDEFINED, nullptr, nullptr,
+ WASM_SYMBOL_UNDEFINED, nullptr, signature,
false);
}
@@ -1198,7 +1199,8 @@ static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
continue;
Symbol *real = addUndefined(saver().save("__real_" + name));
- Symbol *wrap = addUndefined(saver().save("__wrap_" + name));
+ Symbol *wrap =
+ addUndefined(saver().save("__wrap_" + name), sym->getSignature());
v.push_back({sym, real, wrap});
// We want to tell LTO not to inline symbols to be overwritten
diff --git a/lld/wasm/SyntheticSections.cpp b/lld/wasm/SyntheticSections.cpp
index 399a5084e6595..5e7b9c229f3ed 100644
--- a/lld/wasm/SyntheticSections.cpp
+++ b/lld/wasm/SyntheticSections.cpp
@@ -196,7 +196,9 @@ void ImportSection::addImport(Symbol *sym) {
StringRef module = sym->importModule.value_or(defaultModule);
StringRef name = sym->importName.value_or(sym->getName());
if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
- ImportKey<WasmSignature> key(*(f->getSignature()), module, name);
+ const WasmSignature *sig = f->getSignature();
+ assert(sig && "imported functions must have a signature");
+ ImportKey<WasmSignature> key(*sig, module, name);
auto entry = importedFunctions.try_emplace(key, numImportedFunctions);
if (entry.second) {
importedSymbols.emplace_back(sym);
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@llvm/pr-subscribers-lld Author: Lukas Döllerer (Lukasdoe) ChangesWhen wrapping a symbol So far, no valid signature has been attached to the undefined symbol, leading to a nullptr dereference in the logic for creating the import section. This change adds the correct signature to the wrapped symbol, enabling the generation of an import for it. Full diff: https://github.com/llvm/llvm-project/pull/169656.diff 3 Files Affected:
diff --git a/lld/test/wasm/wrap_import.s b/lld/test/wasm/wrap_import.s
new file mode 100644
index 0000000000000..526c1f539a4fd
--- /dev/null
+++ b/lld/test/wasm/wrap_import.s
@@ -0,0 +1,36 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
+# RUN: wasm-ld -emit-relocs -wrap nosuchsym -wrap foo -allow-undefined -o %t.wasm %t.o
+# RUN: obj2yaml %t.wasm | FileCheck %s
+
+.globl foo
+.globl _start
+
+foo:
+ .functype foo () -> (i32)
+ i32.const 1
+ end_function
+
+_start:
+ .functype _start () -> ()
+ call foo
+ drop
+ end_function
+
+# CHECK: - Type: IMPORT
+# CHECK-NEXT: Imports:
+# CHECK-NEXT: - Module: env
+# CHECK-NEXT: Field: __wrap_foo
+# CHECK-NEXT: Kind: FUNCTION
+# CHECK-NEXT SigIndex: 0
+
+# CHECK: - Type: CODE
+# CHECK-NEXT: Relocations:
+# CHECK-NEXT: - Type: R_WASM_FUNCTION_INDEX_LEB
+# CHECK-NEXT: Index: 1
+# CHECK-NEXT: Offset: 0x4
+
+# CHECK: FunctionNames:
+# CHECK-NEXT: - Index: 0
+# CHECK-NEXT: Name: __wrap_foo
+# CHECK-NEXT: - Index: 1
+# CHECK-NEXT: Name: _start
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index fac166587cb9b..97e50783985a8 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -1173,9 +1173,10 @@ struct WrappedSymbol {
Symbol *wrap;
};
-static Symbol *addUndefined(StringRef name) {
+static Symbol *addUndefined(StringRef name,
+ const WasmSignature *signature = nullptr) {
return symtab->addUndefinedFunction(name, std::nullopt, std::nullopt,
- WASM_SYMBOL_UNDEFINED, nullptr, nullptr,
+ WASM_SYMBOL_UNDEFINED, nullptr, signature,
false);
}
@@ -1198,7 +1199,8 @@ static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
continue;
Symbol *real = addUndefined(saver().save("__real_" + name));
- Symbol *wrap = addUndefined(saver().save("__wrap_" + name));
+ Symbol *wrap =
+ addUndefined(saver().save("__wrap_" + name), sym->getSignature());
v.push_back({sym, real, wrap});
// We want to tell LTO not to inline symbols to be overwritten
diff --git a/lld/wasm/SyntheticSections.cpp b/lld/wasm/SyntheticSections.cpp
index 399a5084e6595..5e7b9c229f3ed 100644
--- a/lld/wasm/SyntheticSections.cpp
+++ b/lld/wasm/SyntheticSections.cpp
@@ -196,7 +196,9 @@ void ImportSection::addImport(Symbol *sym) {
StringRef module = sym->importModule.value_or(defaultModule);
StringRef name = sym->importName.value_or(sym->getName());
if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
- ImportKey<WasmSignature> key(*(f->getSignature()), module, name);
+ const WasmSignature *sig = f->getSignature();
+ assert(sig && "imported functions must have a signature");
+ ImportKey<WasmSignature> key(*sig, module, name);
auto entry = importedFunctions.try_emplace(key, numImportedFunctions);
if (entry.second) {
importedSymbols.emplace_back(sym);
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| # CHECK: - Type: CODE | ||
| # CHECK-NEXT: Relocations: | ||
| # CHECK-NEXT: - Type: R_WASM_FUNCTION_INDEX_LEB | ||
| # CHECK-NEXT: Index: 1 |
There was a problem hiding this comment.
Is this the right value here for the relocation? Shouldn't it be function zero (i.e. the __wrap_foo import) that is called here? It is this index 1 in the symbol table? If so you we should probably show the symbol table here too. (or just drop the Relocations and emit-relocs flag completely?)
Could be a bug in --emit-relocs maybe?
There was a problem hiding this comment.
I just stepped through the code a bit and I think this is intended behavior.
- Type: CODE
Relocations:
- Type: R_WASM_FUNCTION_INDEX_LEB
Index: 1
Offset: 0x4
Functions:
- Index: 1
Locals: []
Body: 1080808080000B
- Type: CUSTOM
Name: linking
Version: 2
SymbolTable:
- Index: 0
Kind: FUNCTION
Name: _start
Flags: [ ]
Function: 1
- Index: 1
Kind: FUNCTION
Name: __wrap_foo
Flags: [ UNDEFINED ]
Function: 0
- Type: CUSTOM
Name: name
FunctionNames:
- Index: 0
Name: __wrap_foo
- Index: 1
Name: _start
The symbol index is a different one than the function index. __wrap_foo has symbol index 1, which is why the relocation is emitted for index 1, while _start has function index 1, explaining why this function is shown.
sbc100
changed the title
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3 participants
When wrapping a symbol
foovia-wrap=foo, we create the symbol__wrap_foothat replaces all mentions offoo. This feature was implemented for wasm-ld in commit a5ca34e.So far, no valid signature has been attached to the undefined symbol, leading to a nullptr dereference in the logic for creating the import section. This change adds the correct signature to the wrapped symbol, enabling the generation of an import for it.