[llvm-objcopy] preserve file ownership when overwritten by root

As of binutils 2.36, GNU strip calls chown(2) for "sudo strip foo" and
"sudo strip foo -o foo", but no "sudo strip foo -o bar" or "sudo strip
foo -o ./foo". In other words, while "sudo strip foo -o bar" creates a
new file bar with root access, "sudo strip foo" will keep the owner and
group of foo unchanged. Currently llvm-objcopy and llvm-strip behave
differently, always changing the owner and gropu to root. The
discrepancy prevents Chrome OS from migrating to llvm-objcopy and
llvm-strip as they change file ownership and cause intended users/groups
to lose access when invoked by sudo with the following sequence
(recommended in man page of GNU strip).

1.<Link the executable as normal.>
1.<Copy "foo" to "foo.full">
1.<Run "strip --strip-debug foo">
1.<Run "objcopy --add-gnu-debuglink=foo.full foo">

This patch makes llvm-objcopy and llvm-strip follow GNU's behavior.

Link: crbug.com/1108880

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index 7fd2acd..42d97b2 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -310,7 +310,10 @@ static Error executeObjcopy(CopyConfig &Config) {
       if (Error E = executeObjcopyOnArchive(Config, *Ar))
         return E;
     } else {
-      FileBuffer FB(Config.OutputFilename);
+      FileBuffer FB(Config.OutputFilename,
+                    Config.InputFilename != "-" &&
+                        Config.InputFilename == Config.OutputFilename,
+                    Stat.getUser(), Stat.getGroup());
       if (Error E = executeObjcopyOnBinary(Config,
                                            *BinaryOrErr.get().getBinary(), FB))
         return E;