[clang] 89d5635 - [lld][WebAssembly] Add --keep-section flag
Sam Clegg via cfe-commits
cfe-commits at lists.llvm.org
Thu Nov 2 14:24:21 PDT 2023
Author: Sam Clegg
Date: 2023-11-02T14:23:45-07:00
New Revision: 89d5635f0a834e53ac5446c6d6ea38d9166b2a55
URL: https://github.com/llvm/llvm-project/commit/89d5635f0a834e53ac5446c6d6ea38d9166b2a55
DIFF: https://github.com/llvm/llvm-project/commit/89d5635f0a834e53ac5446c6d6ea38d9166b2a55.diff
LOG: [lld][WebAssembly] Add --keep-section flag
This flag causes wasm-ld preserve a section even in the face of
`--strip-all`. This is useful, for example, to preserve the
target_features section in the ase of clang (which can run wasm-opt
after linking), and emcc (which performs a bunch of post-link work).
Fixes: https://github.com/llvm/llvm-project/issues/60613
Fixes: https://github.com/llvm/llvm-project/issues/55781
Differential Revision: https://reviews.llvm.org/D149917
Added:
lld/test/wasm/strip-all.s
Modified:
clang/lib/Driver/ToolChains/WebAssembly.cpp
lld/wasm/Config.h
lld/wasm/Driver.cpp
lld/wasm/Options.td
lld/wasm/SyntheticSections.h
Removed:
lld/test/wasm/strip-all.test
################################################################################
diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
index fe0b30b7250b824..f04018179a5dab7 100644
--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -141,14 +141,25 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back("-o");
CmdArgs.push_back(Output.getFilename());
+ // When optimizing, if wasm-opt is available, run it.
+ std::string WasmOptPath;
+ if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+ WasmOptPath = ToolChain.GetProgramPath("wasm-opt");
+ if (WasmOptPath == "wasm-opt") {
+ WasmOptPath = {};
+ }
+ }
+
+ if (!WasmOptPath.empty()) {
+ CmdArgs.push_back("--keep-section=target_features");
+ }
+
C.addCommand(std::make_unique<Command>(JA, *this,
ResponseFileSupport::AtFileCurCP(),
Linker, CmdArgs, Inputs, Output));
- // When optimizing, if wasm-opt is available, run it.
if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
- auto WasmOptPath = ToolChain.GetProgramPath("wasm-opt");
- if (WasmOptPath != "wasm-opt") {
+ if (!WasmOptPath.empty()) {
StringRef OOpt = "s";
if (A->getOption().matches(options::OPT_O4) ||
A->getOption().matches(options::OPT_Ofast))
@@ -160,13 +171,13 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
if (OOpt != "0") {
const char *WasmOpt = Args.MakeArgString(WasmOptPath);
- ArgStringList CmdArgs;
- CmdArgs.push_back(Output.getFilename());
- CmdArgs.push_back(Args.MakeArgString(llvm::Twine("-O") + OOpt));
- CmdArgs.push_back("-o");
- CmdArgs.push_back(Output.getFilename());
+ ArgStringList OptArgs;
+ OptArgs.push_back(Output.getFilename());
+ OptArgs.push_back(Args.MakeArgString(llvm::Twine("-O") + OOpt));
+ OptArgs.push_back("-o");
+ OptArgs.push_back(Output.getFilename());
C.addCommand(std::make_unique<Command>(
- JA, *this, ResponseFileSupport::AtFileCurCP(), WasmOpt, CmdArgs,
+ JA, *this, ResponseFileSupport::AtFileCurCP(), WasmOpt, OptArgs,
Inputs, Output));
}
}
diff --git a/lld/test/wasm/strip-all.s b/lld/test/wasm/strip-all.s
new file mode 100644
index 000000000000000..b0819a29f8028a4
--- /dev/null
+++ b/lld/test/wasm/strip-all.s
@@ -0,0 +1,36 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.start.o
+# RUN: wasm-ld --strip-all -o %t.wasm %t.start.o
+# RUN: obj2yaml %t.wasm | FileCheck %s
+#
+## Test alias -s
+# RUN: wasm-ld -s -o %t2.wasm %t.start.o
+# RUN: obj2yaml %t2.wasm | FileCheck %s
+#
+## Check that there is no name section
+# CHECK-NOT: Name: name
+# CHECK-NOT: Name: target_features
+#
+## Test --keep-section=name preserver the name section
+# RUN: wasm-ld --strip-all --keep-section=name -o %t3.wasm %t.start.o
+# RUN: obj2yaml %t3.wasm | FileCheck --check-prefix=CHECK-NAME %s
+#
+# CHECK-NAME: Name: name
+# CHECK-NAME-NOT: Name: target_features
+#
+## Test --keep-section can be specified more than once
+# RUN: wasm-ld --strip-all --keep-section=name --keep-section=target_features -o %t4.wasm %t.start.o
+# RUN: obj2yaml %t4.wasm | FileCheck --check-prefix=CHECK-FEATURES %s
+#
+# CHECK-FEATURES: Name: name
+# CHECK-FEATURES: Name: target_features
+
+ .globl _start
+_start:
+ .functype _start () -> ()
+ end_function
+
+.section .custom_section.target_features,"",@
+.int8 1
+.int8 43
+.int8 15
+.ascii "mutable-globals"
diff --git a/lld/test/wasm/strip-all.test b/lld/test/wasm/strip-all.test
deleted file mode 100644
index ae3314f30676c50..000000000000000
--- a/lld/test/wasm/strip-all.test
+++ /dev/null
@@ -1,10 +0,0 @@
-RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/start.s -o %t.start.o
-RUN: wasm-ld --strip-all -o %t.wasm %t.start.o
-RUN: obj2yaml %t.wasm | FileCheck %s
-
-# Test alias -s
-RUN: wasm-ld -s -o %t.wasm %t.start.o
-RUN: obj2yaml %t.wasm | FileCheck %s
-
-# Check that there is no name section
-CHECK-NOT: Name: name
diff --git a/lld/wasm/Config.h b/lld/wasm/Config.h
index 876c7e80ba80d93..d76d43852acffed 100644
--- a/lld/wasm/Config.h
+++ b/lld/wasm/Config.h
@@ -49,6 +49,7 @@ struct Configuration {
bool extendedConst;
bool growableTable;
bool gcSections;
+ llvm::StringSet<> keepSections;
std::optional<std::pair<llvm::StringRef, llvm::StringRef>> memoryImport;
std::optional<llvm::StringRef> memoryExport;
bool sharedMemory;
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index c2f5f0185781f36..f8b0fc357bd90c2 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -478,6 +478,8 @@ static void readConfigs(opt::InputArgList &args) {
config->relocatable = args.hasArg(OPT_relocatable);
config->gcSections =
args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, !config->relocatable);
+ for (auto *arg : args.filtered(OPT_keep_section))
+ config->keepSections.insert(arg->getValue());
config->mergeDataSegments =
args.hasFlag(OPT_merge_data_segments, OPT_no_merge_data_segments,
!config->relocatable);
diff --git a/lld/wasm/Options.td b/lld/wasm/Options.td
index bb764396bf4df14..2df6196d5e8ce64 100644
--- a/lld/wasm/Options.td
+++ b/lld/wasm/Options.td
@@ -193,6 +193,9 @@ def growable_table: FF<"growable-table">,
def global_base: JJ<"global-base=">,
HelpText<"Memory offset at which to place global data (Defaults to 1024)">;
+defm keep_section: Eq<"keep-section",
+ "Preserve a section even when --strip-all is given. This is useful for compiler drivers such as clang or emcc that, for example, depend on the features section for post-link processing. Can be specified multiple times to keep multiple sections">;
+
def import_memory: FF<"import-memory">,
HelpText<"Import the module's memory from the default module of \"env\" with the name \"memory\".">;
def import_memory_with_name: JJ<"import-memory=">,
diff --git a/lld/wasm/SyntheticSections.h b/lld/wasm/SyntheticSections.h
index 915b35dd6fed804..11479962956aaa1 100644
--- a/lld/wasm/SyntheticSections.h
+++ b/lld/wasm/SyntheticSections.h
@@ -373,7 +373,11 @@ class NameSection : public SyntheticSection {
NameSection(ArrayRef<OutputSegment *> segments)
: SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "name"),
segments(segments) {}
- bool isNeeded() const override { return !config->stripAll && numNames() > 0; }
+ bool isNeeded() const override {
+ if (config->stripAll && !config->keepSections.count(name))
+ return false;
+ return numNames() > 0;
+ }
void writeBody() override;
unsigned numNames() const {
// We always write at least one name which is the name of the
@@ -393,7 +397,9 @@ class ProducersSection : public SyntheticSection {
ProducersSection()
: SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "producers") {}
bool isNeeded() const override {
- return !config->stripAll && fieldCount() > 0;
+ if (config->stripAll && !config->keepSections.count(name))
+ return false;
+ return fieldCount() > 0;
}
void writeBody() override;
void addInfo(const llvm::wasm::WasmProducerInfo &info);
@@ -412,7 +418,9 @@ class TargetFeaturesSection : public SyntheticSection {
TargetFeaturesSection()
: SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "target_features") {}
bool isNeeded() const override {
- return !config->stripAll && features.size() > 0;
+ if (config->stripAll && !config->keepSections.count(name))
+ return false;
+ return features.size() > 0;
}
void writeBody() override;
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