sunfish created this revision.
Herald added subscribers: llvm-commits, dexonsmith, aheejin, jgravelle-google,
sbc100, mehdi_amini, dschuff.
Herald added projects: clang, LLVM.
WebAssembly enforces a rule that caller and callee signatures must
match. This means that the traditional technique of passing `main`
`argc` and `argv` even when it doesn't need them doesn't work.
Currently the backend renames `main` to `__original_main`, however this
doesn't interact well with LTO'ing libc, and the name isn't intuitive.
This patch allows us to transition to `__main_argc_argv` instead.
This is currently being discussed in
https://github.com/WebAssembly/tool-conventions/pull/134.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D70700
Files:
clang/lib/AST/Mangle.cpp
clang/lib/Frontend/InitHeaderSearch.cpp
clang/test/CodeGen/wasm-call-main.c
clang/test/CodeGen/wasm-main.c
clang/test/CodeGen/wasm-main_argc_argv.c
llvm/include/llvm/ADT/Triple.h
Index: llvm/include/llvm/ADT/Triple.h
===================================================================
--- llvm/include/llvm/ADT/Triple.h
+++ llvm/include/llvm/ADT/Triple.h
@@ -730,6 +730,11 @@
return getArch() == Triple::riscv32 || getArch() == Triple::riscv64;
}
+ /// Tests whether the target is wasm (32- and 64-bit).
+ bool isWasm() const {
+ return getArch() == Triple::wasm32 || getArch() == Triple::wasm64;
+ }
+
/// Tests whether the target supports comdat
bool supportsCOMDAT() const {
return !isOSBinFormatMachO();
Index: clang/test/CodeGen/wasm-main_argc_argv.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/wasm-main_argc_argv.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Mangle the argc/argv form of main.
+
+int main(int argc, char **argv) {
+ return 0;
+}
+
+// CHECK-LABEL: define i32 @__main_argc_argv(i32 %argc, i8** %argv)
Index: clang/test/CodeGen/wasm-main.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/wasm-main.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Don't mangle the no-arg form of main.
+
+int main(void) {
+ return 0;
+}
+
+// CHECK-LABEL: define i32 @main()
Index: clang/test/CodeGen/wasm-call-main.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/wasm-call-main.c
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple wasm32 -o - -emit-llvm %s | FileCheck %s
+
+// Mangle argc/argv main even when it's not defined in this TU.
+
+#include <stddef.h>
+
+int main(int argc, char *argv[]);
+
+int foo(void) {
+ return main(0, NULL);
+}
+
+// CHECK: call i32 @__main_argc_argv(
Index: clang/lib/Frontend/InitHeaderSearch.cpp
===================================================================
--- clang/lib/Frontend/InitHeaderSearch.cpp
+++ clang/lib/Frontend/InitHeaderSearch.cpp
@@ -435,8 +435,7 @@
break;
case llvm::Triple::UnknownOS:
- if (triple.getArch() == llvm::Triple::wasm32 ||
- triple.getArch() == llvm::Triple::wasm64)
+ if (triple.isWasm())
return;
break;
}
Index: clang/lib/AST/Mangle.cpp
===================================================================
--- clang/lib/AST/Mangle.cpp
+++ clang/lib/AST/Mangle.cpp
@@ -50,7 +50,8 @@
CCM_Fast,
CCM_RegCall,
CCM_Vector,
- CCM_Std
+ CCM_Std,
+ CCM_WasmMainArgcArgv
};
static bool isExternC(const NamedDecl *ND) {
@@ -63,6 +64,14 @@
const NamedDecl *ND) {
const TargetInfo &TI = Context.getTargetInfo();
const llvm::Triple &Triple = TI.getTriple();
+
+ // On wasm, the argc/argv form of "main" is renamed so that the startup code
+ // can call it with the correct function signature.
+ if (Triple.isWasm())
+ if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(ND))
+ if (FD->isMain() && FD->hasPrototype() && FD->param_size() == 2)
+ return CCM_WasmMainArgcArgv;
+
if (!Triple.isOSWindows() ||
!(Triple.getArch() == llvm::Triple::x86 ||
Triple.getArch() == llvm::Triple::x86_64))
@@ -145,6 +154,12 @@
const ASTContext &ASTContext = getASTContext();
CCMangling CC = getCallingConvMangling(ASTContext, D);
+
+ if (CC == CCM_WasmMainArgcArgv) {
+ Out << "__main_argc_argv";
+ return;
+ }
+
bool MCXX = shouldMangleCXXName(D);
const TargetInfo &TI = Context.getTargetInfo();
if (CC == CCM_Other || (MCXX && TI.getCXXABI() == TargetCXXABI::Microsoft)) {
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