Re: [PATCH 2/2] gcc/riscv: Add a mechanism to remove some calls to _riscv_save_0

[Jim Wilson <jimw at sifive dot com>]

On Sun, Aug 25, 2019 at 9:40 AM Jim Wilson <jimw@sifive.com> wrote:
> The problem with the linux toolchain support for -msave-restore is
> that we forgot to add a version script to export the symbols.  I made
> the obvious change to add a RISC-V specific libgcc version script, and
> now everything in the g++ and gfortran testsuites are linking, but the
> execution tests are all timing out.  So there is still something
> wrong.  I need to do some more work here.

Following up on this, I found a linker bug where it was emitting error
messages for non-pic code in shared libraries, but wasn't exiting with
an error, so bad shared libraries were being produced without killing
the build.  I wrote and committed a binutils patch to fix that.  The
underlying problem is that the save/restore functions were always
called as non-pic, even for a shared library.  But fixing that
produced shared libraries that failed again, which turned out because
the save/restore functions use the alternate link register t0/x5 which
is clobbered by plts, so we can't call them in shared libraries at
all.  I wrote and committed a gcc patch to disable -msave-restore when
-fpic is used, and emit a warning message if the user explicitly
turned on -msave-restore.  Since we can't use the save/restore
functions in shared libraries, we don't need to export them or support
pic calls to them, and I dropped those patches.  With these changes
I'm now able to do -msave-restore testing with a linux toolchain.
Testing with and without your patch for a riscv64-linux toolchain, I
see 11 extra gcc failures, 2 extra g++ failures, and 8 extra gfortran
failures.  I didn't look at the details.  I suspect that most of these
are failing for the same reason, and there is only a couple of minor
bugs that need to be fixed to make your patch work.

Jim