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Add -fdebug-prefix-map command line argument #5011

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Add -fdebug-prefix-map command line argument #5011

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aad25b3
cl_options: add -fdebug-prefix-map
yanok Oct 30, 2025
9edb6d4
dibuilder: use debugPrefixMap to remap source locs
yanok Oct 30, 2025
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26 changes: 26 additions & 0 deletions driver/cl_options.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -223,6 +223,32 @@ cl::opt<bool> emitDwarfDebugInfo(
"gdwarf", cl::ZeroOrMore,
cl::desc("Emit DWARF debuginfo (instead of CodeView) for MSVC targets"));

// Prefix map for filenames in DWARF debuginfo
std::map<std::string, std::string> debugPrefixMap;

struct DwarfPrefixParser : public cl::parser<std::string> {
explicit DwarfPrefixParser(cl::Option &O) : cl::parser<std::string>(O) {}

bool parse(cl::Option &O, llvm::StringRef /*ArgName*/, llvm::StringRef Arg,
std::string & /*Val*/) {
auto [from, to] = Arg.split('=');
if (from.empty() || to.empty()) {
return O.error("invalid debug prefix map: " + Arg);
}
auto fromStr = std::string(from);
if (debugPrefixMap.find(fromStr) != debugPrefixMap.end()) {
return O.error("debug prefix map already contains: " + fromStr);
}
debugPrefixMap[fromStr] = std::string(to);
return false;
}
};

static cl::opt<std::string, false, DwarfPrefixParser> fdebugPrefixMap(
"fdebug-prefix-map", cl::ZeroOrMore,
cl::desc("Prefix map for filenames in DWARF debuginfo"),
cl::value_desc("<old>=<new>"));

cl::opt<bool> noAsm("noasm", cl::desc("Disallow use of inline assembler"),
cl::ZeroOrMore);

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3 changes: 3 additions & 0 deletions driver/cl_options.h
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Expand Up @@ -20,6 +20,7 @@
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/CommandLine.h"
#include <map>
#include <deque>
#include <vector>

Expand Down Expand Up @@ -149,4 +150,6 @@ extern cl::opt<bool> dynamicCompileTlsWorkaround;
#else
constexpr bool enableDynamicCompile = false;
#endif
// Prefix map for filenames in DWARF debuginfo
extern std::map<std::string, std::string> debugPrefixMap;
}
15 changes: 12 additions & 3 deletions gen/dibuilder.cpp
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Expand Up @@ -218,6 +218,15 @@ void DIBuilder::SetValue(Loc loc, llvm::Value *value,
IR->scopebb());
}

std::string DIBuilder::remapDIPath(llvm::StringRef path) {
for (const auto &[from, to] : opts::debugPrefixMap) {
if (path.starts_with(from)) {
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@JohanEngelen JohanEngelen Nov 1, 2025

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starts_with looks dangerous, what if I map "some/path="other/thing", does that mean that "some/path_more" also matches and is remapped?

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@JohanEngelen JohanEngelen Nov 1, 2025

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(could be checked in a test case)

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@yanok yanok Nov 2, 2025

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Yes, but this is what clang does. I guess in the most (only?) use cases this is going to be some "root" path, so we don't expect sources from root_some to be passed to the compiler. Cautious people can do some/path/=other/thing/. It's easy to enforce this in the code, but I don't want to diverge from clang...

return to + path.substr(from.size()).str();
}
}
return std::string(path);
}

DIFile DIBuilder::CreateFile(const char *filename) {
if (!filename)
filename = IR->dmodule->srcfile.toChars();
Expand All @@ -231,14 +240,14 @@ DIFile DIBuilder::CreateFile(const char *filename) {
// ...)

if (llvm::sys::path::is_absolute(filename)) {
return DBuilder.createFile(llvm::sys::path::relative_path(filename),
llvm::sys::path::root_path(filename));
return DBuilder.createFile(remapDIPath(llvm::sys::path::relative_path(filename)),
remapDIPath(llvm::sys::path::root_path(filename)));
}

llvm::SmallString<128> cwd;
llvm::sys::fs::current_path(cwd);

return DBuilder.createFile(filename, cwd);
return DBuilder.createFile(remapDIPath(filename), remapDIPath(cwd));
}

DIFile DIBuilder::CreateFile(Loc loc) {
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1 change: 1 addition & 0 deletions gen/dibuilder.h
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Expand Up @@ -163,6 +163,7 @@ class DIBuilder {
llvm::SmallVector<llvm::Metadata *, 16> &elems);
void AddStaticMembers(AggregateDeclaration *sd, ldc::DIFile file,
llvm::SmallVector<llvm::Metadata *, 16> &elems);
std::string remapDIPath(llvm::StringRef path);
DIFile CreateFile(const char *filename = nullptr);
DIFile CreateFile(Loc loc);
DIFile CreateFile(Dsymbol *decl);
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