Darwin: introduce a global override for debug prefix map entries

[aprantl]

Summary

This patch adds a new Darwin clang driver environment variable in the spirit of RC_DEBUG_OPTIONS, called RC_DEBUG_PREFIX_MAP, which allows a meta build tool to add one additional -fdebug-prefix-map entry without the knowledge of the build system.

rdar://85224675

[arphaman]

clang/lib/Driver/ToolChains/Clang.cpp

688

Suggestion: It might be good to factor out the code that verifies the value and either produces an error or adds an argument into some common helper as it's used right above this codepath as well.

[aprantl]

Refactored code.

clang/lib/Driver/ToolChains/Clang.cpp

688

Good idea! Done.

[thakis]

(I wish there was a flag that said "clang, never ever read any env vars please". Some people think that builds should be deterministic and not depend on random env vars people might have set (and then not do correct incremental rebuilds when the value of such env var flags change). But given that clang already reads a whole bunch of such env vars and we can always add such a flag later, I suppose this change doesn't make things that much worse.)

[aprantl]

In D119850#3326266, @thakis wrote:

(I wish there was a flag that said "clang, never ever read any env vars please". Some people think that builds should be deterministic and not depend on random env vars people might have set (and then not do correct incremental rebuilds when the value of such env var flags change). But given that clang already reads a whole bunch of such env vars and we can always add such a flag later, I suppose this change doesn't make things that much worse.)

These are all good points. The environment variables are useful to side-step the many project-specific build systems that you have to deal with when building an entire OS and this is also the primary use-case here.

clang/include/clang/Driver/ToolChain.h

public:
   virtual codegenoptions::DebugInfoFormat getDefaultDebugFormat() const {
     return codegenoptions::DIF_DWARF;
   }
 
   /// UseDwarfDebugFlags - Embed the compile options to clang into the Dwarf
   /// compile unit information.
   virtual bool UseDwarfDebugFlags() const { return false; }
 
+  /// Add an additional -fdebug-prefix-map entry.
+  virtual std::string GetGlobalDebugPathRemapping() const { return {}; }
+  
   // Return the DWARF version to emit, in the absence of arguments
   // to the contrary.
   virtual unsigned GetDefaultDwarfVersion() const { return 5; }
 
   // Some toolchains may have different restrictions on the DWARF version and
   // may need to adjust it. E.g. NVPTX may need to enforce DWARF2 even when host
   // compilation uses DWARF5.
   virtual unsigned getMaxDwarfVersion() const { return UINT_MAX; }

clang/lib/Driver/ToolChains/Clang.cpp

if (ObjFileNameForDebug != "-" &&
     // Make the path absolute in the debug infos like MSVC does.
     llvm::sys::fs::make_absolute(ObjFileNameForDebug);
   }
   CmdArgs.push_back(
       Args.MakeArgString(Twine("-object-file-name=") + ObjFileNameForDebug));
 }
 
 /// Add a CC1 and CC1AS option to specify the debug file path prefix map.
-static void addDebugPrefixMapArg(const Driver &D, const ArgList &Args, ArgStringList &CmdArgs) {
-  for (const Arg *A : Args.filtered(options::OPT_ffile_prefix_map_EQ,
-                                    options::OPT_fdebug_prefix_map_EQ)) {
-    StringRef Map = A->getValue();
+static void addDebugPrefixMapArg(const Driver &D, const ToolChain &TC,
+                                 const ArgList &Args, ArgStringList &CmdArgs) {
+  auto AddOneArg = [&](StringRef Map, StringRef Name) {
     if (!Map.contains('='))
-      D.Diag(diag::err_drv_invalid_argument_to_option)
-          << Map << A->getOption().getName();
+      D.Diag(diag::err_drv_invalid_argument_to_option) << Map << Name;
     else
       CmdArgs.push_back(Args.MakeArgString("-fdebug-prefix-map=" + Map));
+  };
+
+  for (const Arg *A : Args.filtered(options::OPT_ffile_prefix_map_EQ,
+                                    options::OPT_fdebug_prefix_map_EQ)) {
+    AddOneArg(A->getValue(), A->getOption().getName());
     A->claim();
   }
+  std::string GlobalRemapEntry = TC.GetGlobalDebugPathRemapping();
+  if (GlobalRemapEntry.empty())
+    return;
+  AddOneArg(GlobalRemapEntry, "environment");
 }
 
 /// Add a CC1 and CC1AS option to specify the macro file path prefix map.
 static void addMacroPrefixMapArg(const Driver &D, const ArgList &Args,
                                  ArgStringList &CmdArgs) {
   for (const Arg *A : Args.filtered(options::OPT_ffile_prefix_map_EQ,
                                     options::OPT_fmacro_prefix_map_EQ)) {
     StringRef Map = A->getValue();
#endif
 
   if (!ShouldEnableAutolink(Args, TC, JA))
     CmdArgs.push_back("-fno-autolink");
 
   // Add in -fdebug-compilation-dir if necessary.
   const char *DebugCompilationDir =
       addDebugCompDirArg(Args, CmdArgs, D.getVFS());
 
-  addDebugPrefixMapArg(D, Args, CmdArgs);
+  addDebugPrefixMapArg(D, TC, Args, CmdArgs);
 
   if (Arg *A = Args.getLastArg(options::OPT_ftemplate_depth_,
                                options::OPT_ftemplate_depth_EQ)) {
     CmdArgs.push_back("-ftemplate-depth");
     CmdArgs.push_back(A->getValue());
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_foperator_arrow_depth_EQ)) {
if (SourceAction->getType() == types::TY_Asm ||
       SourceAction->getType() == types::TY_PP_Asm) {
     // You might think that it would be ok to set DebugInfoKind outside of
     // the guard for source type, however there is a test which asserts
     // that some assembler invocation receives no -debug-info-kind,
     // and it's not clear whether that test is just overly restrictive.
     DebugInfoKind = (WantDebug ? codegenoptions::DebugInfoConstructor
                                : codegenoptions::NoDebugInfo);
 
-    addDebugPrefixMapArg(getToolChain().getDriver(), Args, CmdArgs);
+    addDebugPrefixMapArg(getToolChain().getDriver(), getToolChain(), Args,
+                         CmdArgs);
 
     // Set the AT_producer to the clang version when using the integrated
     // assembler on assembly source files.
     CmdArgs.push_back("-dwarf-debug-producer");
     CmdArgs.push_back(Args.MakeArgString(getClangFullVersion()));
 
     // And pass along -I options
     Args.AddAllArgs(CmdArgs, options::OPT_I);

clang/lib/Driver/ToolChains/Darwin.h

public:
 
   bool isPICDefault() const override;
   bool isPIEDefault(const llvm::opt::ArgList &Args) const override;
   bool isPICDefaultForced() const override;
 
   bool SupportsProfiling() const override;
 
   bool UseDwarfDebugFlags() const override;
+  std::string GetGlobalDebugPathRemapping() const override;
 
   llvm::ExceptionHandling
   GetExceptionModel(const llvm::opt::ArgList &Args) const override {
     return llvm::ExceptionHandling::None;
   }
 
   virtual StringRef getOSLibraryNameSuffix(bool IgnoreSim = false) const {
     return "";

clang/lib/Driver/ToolChains/Darwin.cpp

 }
 
 bool MachO::UseDwarfDebugFlags() const {
   if (const char *S = ::getenv("RC_DEBUG_OPTIONS"))
     return S[0] != '\0';
   return false;
 }
 
+std::string MachO::GetGlobalDebugPathRemapping() const {
+  if (const char *S = ::getenv("RC_DEBUG_PREFIX_MAP"))
+    return S;
+  return {};
+}
+
 llvm::ExceptionHandling Darwin::GetExceptionModel(const ArgList &Args) const {
   // Darwin uses SjLj exceptions on ARM.
   if (getTriple().getArch() != llvm::Triple::arm &&
       getTriple().getArch() != llvm::Triple::thumb)
     return llvm::ExceptionHandling::None;
 
   // Only watchOS uses the new DWARF/Compact unwinding method.
   llvm::Triple Triple(ComputeLLVMTriple(Args));

clang/test/Driver/darwin-debug-prefix-map.c

+// RUN: env RC_DEBUG_PREFIX_MAP=old=new \
+// RUN:  %clang -target arm64-apple-darwin -### -c -g %s 2>&1 | FileCheck %s
+// RUN: env RC_DEBUG_PREFIX_MAP=illegal \
+// RUN:  %clang -target arm64-apple-darwin -### -c -g %s 2>&1 | FileCheck %s --check-prefix=ERR
+// CHECK: "-fdebug-prefix-map=old=new" 
+// ERR: invalid argument 'illegal'

clang/test/Driver/darwin-debug-prefix-map.s

+// RUN: env RC_DEBUG_PREFIX_MAP=old=new \
+// RUN:  %clang -target arm64-apple-darwin -### -c -g %s 2>&1 | FileCheck %s
+// RUN: env RC_DEBUG_PREFIX_MAP=illegal \
+// RUN:  %clang -target arm64-apple-darwin -### -c -g %s 2>&1 | FileCheck %s --check-prefix=ERR
+// CHECK: "-fdebug-prefix-map=old=new" 
+// ERR: invalid argument 'illegal'