(original) (raw)

On Oct 18, 2016, at 8:30 PM, Hal Finkel <hfinkel@anl.gov> wrote:

----- Original Message -----
From: "Mehdi Amini via llvm-dev" <llvm-dev@lists.llvm.org>
To: "Rui Ueyama" <ruiu@google.com>
Cc: "llvm-dev" <llvm-dev@lists.llvm.org>
Sent: Tuesday, October 18, 2016 10:22:00 PM
Subject: Re: \[llvm-dev\] Embedding LLD version to executables

On Oct 18, 2016, at 6:44 PM, Rui Ueyama via llvm-dev
<llvm-dev@lists.llvm.org> wrote:

I'd like to make LLD embed version information so that we can
determine if an executable was created by LLD and if that's the
case which version of LLD.

Pardon my ignorance, but what’s the motivation?

We don’t embed the clang version in every binary clang generates for
instance.

We do. Clang outputs an "ident" comment with its version information, and that ends up in the object files (at least on Linux).

Interesting, we don’t on Darwin:

$ echo "int main() {}" | clang -x c -o - - -S | grep clang

$ echo "int main() {}" | clang -x c -o - - -S -target x86\_64-pc-linux-gnu | grep clang

.ident "Apple LLVM version 8.0.0 (clang-800.0.42.1)”

Dos it show up in the final binary? If yes, how does it behave when you mix-and-match versions in different .o?

Also I’m still not sure why doing this?

—

Mehdi

ld.bfd doesn't seem to embed any information, so we cannot tell
whether an executable was linked by ld.bfd or not easily.

ld.gold embeds a string "GNU gold " as
".note.gnu.gold-version" section contents.

I'm wondering what we should do for LLD. The gold's way seems
almost right, but I think we don't want to use the same section
name because it contains "gold" as part of the section name.
However, at the same time, I don't believe we want to create
".note.gnu.lld-version", because if we do, all programs that
determine linker version need to look at
".note.gnu.-version" for all known linkers. That's
absurd. (Also, our product is not GNU, so ".gnu" part is probably
irrelevant.)

I'm leaning towards ".note.linker-version" in hope that other
linkers follow it.

At least that would look much better than a .gnu.xxxx

I agree.

-Hal

—
Mehdi

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
LLVM Developers mailing list
llvm-dev@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory