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Give same-named members unique timestamps on Darwin in llvm-ar.

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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

llvm-svn: 343805
This commit is contained in:
James Y Knight 2018-10-04 18:49:21 +00:00
parent b02a6ea2c1
commit 699b43fe0e
2 changed files with 91 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

77
lib/Object/ArchiveWriter.cpp
View File

@ -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_ostream &Out, uint64_t Pos,
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_ostream &SymNames, bool &HasObject) {
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 &StringTable, raw_ostream &SymNames,
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 &StringTable, raw_ostream &SymNames,
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 ArcName,
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;

21
test/Object/archive-darwin-duplicates.test Normal file
View File

@ -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