[llvm] r343805 - Give same-named members unique timestamps on Darwin in llvm-ar.
James Y Knight via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 4 11:49:22 PDT 2018
Author: jyknight
Date: Thu Oct 4 11:49:21 2018
New Revision: 343805
URL: http://llvm.org/viewvc/llvm-project?rev=343805&view=rev
Log:
Give same-named members unique timestamps on Darwin in llvm-ar.
This change ensures that the (membername,timestamp) tuple uniquely
identifies an entry in an archive for format=darwin, in deterministic
mode (which is the default).
That, then, enables lldb and dsymutil to locate the appropriate object
within the archive.
Differential Revision: https://reviews.llvm.org/D47659
Added:
llvm/trunk/test/Object/archive-darwin-duplicates.test
Modified:
llvm/trunk/lib/Object/ArchiveWriter.cpp
Modified: llvm/trunk/lib/Object/ArchiveWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/ArchiveWriter.cpp?rev=343805&r1=343804&r2=343805&view=diff
==============================================================================
--- llvm/trunk/lib/Object/ArchiveWriter.cpp (original)
+++ llvm/trunk/lib/Object/ArchiveWriter.cpp Thu Oct 4 11:49:21 2018
@@ -27,6 +27,8 @@
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/raw_ostream.h"
+#include <map>
+
#if !defined(_MSC_VER) && !defined(__MINGW32__)
#include <unistd.h>
#else
@@ -245,18 +247,20 @@ static void printMemberHeader(raw_ostrea
raw_ostream &StringTable,
object::Archive::Kind Kind, bool Thin,
StringRef ArcName, const NewArchiveMember &M,
+ sys::TimePoint<std::chrono::seconds> ModTime,
unsigned Size) {
+
if (isBSDLike(Kind))
- return printBSDMemberHeader(Out, Pos, M.MemberName, M.ModTime, M.UID, M.GID,
+ return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
M.Perms, Size);
if (!useStringTable(Thin, M.MemberName))
- return printGNUSmallMemberHeader(Out, M.MemberName, M.ModTime, M.UID, M.GID,
+ return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
M.Perms, Size);
Out << '/';
uint64_t NamePos = StringTable.tell();
addToStringTable(StringTable, ArcName, M, Thin);
printWithSpacePadding(Out, NamePos, 15);
- printRestOfMemberHeader(Out, M.ModTime, M.UID, M.GID, M.Perms, Size);
+ printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
}
namespace {
@@ -411,7 +415,7 @@ getSymbols(MemoryBufferRef Buf, raw_ostr
static Expected<std::vector<MemberData>>
computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
object::Archive::Kind Kind, bool Thin, StringRef ArcName,
- ArrayRef<NewArchiveMember> NewMembers) {
+ bool Deterministic, ArrayRef<NewArchiveMember> NewMembers) {
static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
// This ignores the symbol table, but we only need the value mod 8 and the
@@ -420,6 +424,59 @@ computeMemberData(raw_ostream &StringTab
std::vector<MemberData> Ret;
bool HasObject = false;
+
+ // UniqueTimestamps is a special case to improve debugging on Darwin:
+ //
+ // The Darwin linker does not link debug info into the final
+ // binary. Instead, it emits entries of type N_OSO in in the output
+ // binary's symbol table, containing references to the linked-in
+ // object files. Using that reference, the debugger can read the
+ // debug data directly from the object files. Alternatively, an
+ // invocation of 'dsymutil' will link the debug data from the object
+ // files into a dSYM bundle, which can be loaded by the debugger,
+ // instead of the object files.
+ //
+ // For an object file, the N_OSO entries contain the absolute path
+ // path to the file, and the file's timestamp. For an object
+ // included in an archive, the path is formatted like
+ // "/absolute/path/to/archive.a(member.o)", and the timestamp is the
+ // archive member's timestamp, rather than the archive's timestamp.
+ //
+ // However, this doesn't always uniquely identify an object within
+ // an archive -- an archive file can have multiple entries with the
+ // same filename. (This will happen commonly if the original object
+ // files started in different directories.) The only way they get
+ // distinguished, then, is via the timestamp. But this process is
+ // unable to find the correct object file in the archive when there
+ // are two files of the same name and timestamp.
+ //
+ // Additionally, timestamp==0 is treated specially, and causes the
+ // timestamp to be ignored as a match criteria.
+ //
+ // That will "usually" work out okay when creating an archive not in
+ // deterministic timestamp mode, because the objects will probably
+ // have been created at different timestamps.
+ //
+ // To ameliorate this problem, in deterministic archive mode (which
+ // is the default), on Darwin we will emit a unique non-zero
+ // timestamp for each entry with a duplicated name. This is still
+ // deterministic: the only thing affecting that timestamp is the
+ // order of the files in the resultant archive.
+ //
+ // See also the functions that handle the lookup:
+ // in lldb: ObjectContainerBSDArchive::Archive::FindObject()
+ // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
+ bool UniqueTimestamps =
+ Deterministic && (Kind == object::Archive::K_DARWIN ||
+ Kind == object::Archive::K_DARWIN64);
+ std::map<StringRef, unsigned> FilenameCount;
+ if (UniqueTimestamps) {
+ for (const NewArchiveMember &M : NewMembers)
+ FilenameCount[M.MemberName]++;
+ for (auto &Entry : FilenameCount)
+ Entry.second = Entry.second > 1 ? 1 : 0;
+ }
+
for (const NewArchiveMember &M : NewMembers) {
std::string Header;
raw_string_ostream Out(Header);
@@ -437,7 +494,13 @@ computeMemberData(raw_ostream &StringTab
unsigned TailPadding = OffsetToAlignment(Data.size() + MemberPadding, 2);
StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
- printMemberHeader(Out, Pos, StringTable, Kind, Thin, ArcName, M,
+ sys::TimePoint<std::chrono::seconds> ModTime;
+ if (UniqueTimestamps)
+ // Increment timestamp for each file of a given name.
+ ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
+ else
+ ModTime = M.ModTime;
+ printMemberHeader(Out, Pos, StringTable, Kind, Thin, ArcName, M, ModTime,
Buf.getBufferSize() + MemberPadding);
Out.flush();
@@ -469,8 +532,8 @@ Error llvm::writeArchive(StringRef ArcNa
SmallString<0> StringTableBuf;
raw_svector_ostream StringTable(StringTableBuf);
- Expected<std::vector<MemberData>> DataOrErr =
- computeMemberData(StringTable, SymNames, Kind, Thin, ArcName, NewMembers);
+ Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
+ StringTable, SymNames, Kind, Thin, ArcName, Deterministic, NewMembers);
if (Error E = DataOrErr.takeError())
return E;
std::vector<MemberData> &Data = *DataOrErr;
Added: llvm/trunk/test/Object/archive-darwin-duplicates.test
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Object/archive-darwin-duplicates.test?rev=343805&view=auto
==============================================================================
--- llvm/trunk/test/Object/archive-darwin-duplicates.test (added)
+++ llvm/trunk/test/Object/archive-darwin-duplicates.test Thu Oct 4 11:49:21 2018
@@ -0,0 +1,21 @@
+Test that darwin archives are created with distinct (name,timestamp) pairs.
+
+The two members with the duplicated name "test.o" must have unique
+non-zero timestamps, while baz.o, being unique, remains a zero
+timestamp.
+
+RUN: mkdir -p %T/sub1
+RUN: printf test > %T/test.o
+RUN: printf sub1/test > %T/sub1/test.o
+RUN: printf baz > %T/baz.o
+
+RUN: rm -f %t.a
+RUN: llvm-ar -format=darwin rcs %t.a %T/sub1/test.o %T/test.o %T/baz.o
+RUN: FileCheck -strict-whitespace %s < %t.a
+
+CHECK:#1/12 1 0 0 644 28 `
+CHECK-NEXT:test.o
+CHECK:#1/12 2 0 0 644 20 `
+CHECK-NEXT:test.o
+CHECK:#1/12 0 0 0 644 20 `
+CHECK-NEXT:baz.o
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