[Bug c/105305] New: ARM32: gcc does not pass all library directories to linker

[Bug c/105305] New: ARM32: gcc does not pass all library directories to linker

[rui314 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105305

            Bug ID: 105305
           Summary: ARM32: gcc does not pass all library directories to
                    linker
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rui314 at gmail dot com
  Target Milestone: ---

I'm the author of the mold linker (https://github.com/rui314/mold).

As far as I know, gcc always passes all library paths to the linker by -L<dir>,
but I got a bug report that that's not the case on ARM32. It is reported that
gcc does not pass some obvious paths such as `-L/usr` or `-L/usr/lib`. The code
to explicitly exclude "obvious" directories is here:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/gcc.cc;h=bb07cc244e30fbeccc701816db888f497d65eb08;hb=refs/heads/master#l7931

mold and LLVM lld don't have the notion of the default search paths for the
sake of build reproducibility. They guarantee that as long as you pass the
exact same command line options and input files, the linkers behave exactly the
same regardless of the host machine (in LLD, that's guaranteed even across Unix
and Windows.) That helps us a lot when we do cross compilation.

So, can gcc pass all library paths to the linker on ARM32?

https://github.com/rui314/mold/issues/336

[Bug target/105305] ARM32: gcc does not pass all library directories to linker

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105305

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |arm*-*-*

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Gold also didn't search any by default.

[Bug target/105305] ARM32: gcc does not pass all library directories to linker

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105305

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>The code to explicitly exclude "obvious" directories is here

That code has been there since before 1993. So I wonder if all other ld's
always included /usr and /usr/lib by default. It is only the newer ones which
don't.

Does POSIX say anything about ld behavior?

[Bug target/105305] ARM32: gcc does not pass all library directories to linker

[rui314 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105305

--- Comment #3 from Rui Ueyama <rui314 at gmail dot com> ---
By other ld's, what linkers did you have in your mind? If lld, mold and gold
don't hard code /usr and /usr/lib, then the only remaining linker is GNU ld.

It doesn't seem like POSIX says about the default library search paths. I don't
believe POSIX even mandates the existence of /usr and /usr/lib. macOS doesn't
have such directories, but IIUC macOS at least one point in the past certified
as POSIX compliant.