Re: [PATCH 2/3] Fix LIBC_PROG_BINUTILS for -fuse-ld=lld

[Fangrui Song <maskray@google.com>]

On 2021-10-26, Adhemerval Zanella wrote:
>GCC does not print the correct linker when -fuse-ld=lld is used with
>the -print-prog-name=ld:
>
>  $ gcc -v 2>&1 | tail -n 1
>  gcc version 11.2.0 (Ubuntu 11.2.0-7ubuntu2)
>  $ gcc
>  ld
>
>This is different than for gold:
>
>  $ gcc -fuse-ld=gold -print-prog-name=ld
>  ld.gold

I think it may be debatable whether -fuse-ld={bfd,gold,lld} should
affect -print-prog-name=ld output.

   # Should -fuse-ld= do anything with this?
   % aarch64-linux-gnu-gcc -print-prog-name=../bin/ld
   /usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/bin/../bin/ld

gcc/gcc.c has OPT_fuse_ld_bfd but not OPT_fuse_ld_lld, which may explain
the behavior difference.

Clang does not have the GCC -fuse-ld= --print-prog-name=ld behavior.




>Using ld.lld as the static linker name prints the expected result.
>
>This is only required when -fuse-ld=lld is used, if lld is used as
>the 'ld' programs (through a symlink) LIBC_PROG_BINUTILS works
>as expected.
>
>Checked on x86_64-linux-gnu.
>---
> aclocal.m4 | 6 +++++-
> configure  | 6 +++++-
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
>diff --git a/aclocal.m4 b/aclocal.m4
>index c195c4db56..83da631822 100644
>--- a/aclocal.m4
>+++ b/aclocal.m4
>@@ -114,8 +114,12 @@ if test -n "$path_binutils"; then
>     path_binutils=`(cd $path_binutils; pwd) | sed 's%/*$%/%'`
>     CC="$CC -B$path_binutils"
> fi
>+case "$CC" in
>+    *fuse-ld=lld*) LDNAME=ld.lld;;
>+    *)             LDNAME=ld;;

Perhaps hard code -fuse-ld=bfd and -fuse-ld=gold as well?

I think gcc -print-prog-name=ld.bfd is more robust than
gcc -print-prog-name=ld -fuse-ld=bfd.

>+esac
> AS=`$CC -print-prog-name=as`
>-LD=`$CC -print-prog-name=ld`
>+LD=`$CC -print-prog-name=$LDNAME`
> AR=`$CC -print-prog-name=ar`
> AC_SUBST(AR)
> OBJDUMP=`$CC -print-prog-name=objdump`
>diff --git a/configure b/configure
>index 39d75eb4ed..2a28c58cd6 100755
>--- a/configure
>+++ b/configure
>@@ -4549,8 +4549,12 @@ if test -n "$path_binutils"; then
>     path_binutils=`(cd $path_binutils; pwd) | sed 's%/*$%/%'`
>     CC="$CC -B$path_binutils"
> fi
>+case "$CC" in
>+    *fuse-ld=lld*) LDNAME=ld.lld;;
>+    *)             LDNAME=ld;;
>+esac
> AS=`$CC -print-prog-name=as`
>-LD=`$CC -print-prog-name=ld`
>+LD=`$CC -print-prog-name=$LDNAME`
> AR=`$CC -print-prog-name=ar`
>
> OBJDUMP=`$CC -print-prog-name=objdump`
>-- 
>2.32.0
>