Re: [PATCH] Support -fuse-ld=bfd and -fuse-ld=gold

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Nov 29, 2012 at 1:10 AM, Markus Trippelsdorf
<markus@trippelsdorf.de> wrote:
> On 2012.11.29 at 09:43 +0100, Richard Biener wrote:
>> On Thu, Nov 29, 2012 at 5:18 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> > From: "H.J. Lu" <hjl.tools@gmail.com>
>> > To: gcc-patches@gcc.gnu.org
>> > Cc: Joseph Myers  <joseph@codesourcery.com>, Paolo Bonzini <bonzini@gnu.org>
>> > Bcc:
>> > Subject: [PATCH] Support -fuse-ld=bfd and -fuse-ld=gold
>> > Reply-To:
>> >
>> > Hi,
>> >
>> > Binutils supports 2 linkers, ld.gold and ld.bfd.  One of them is
>> > configured as the default linker, ld, which is used by GCC.  Sometimes,
>> > we want to use the alternate linker with GCC at run-time.  This patch
>> > adds -fuse-ld=bfd and -fuse-ld=gold options to GCC driver.  It changes
>> > collect2.c to pick either ld.bfd or ld.gold.  It also adds
>> > ORIGINAL_LD_BFD_FOR_TARGET and ORIGINAL_LD_GOLD_FOR_TARGET to
>> > exec-tool.in to add -fuse-ld=bfd and -fuse-ld=gold support to
>> > collect-ld.  Since ld.bfd nor ld.gold know the new options, you
>> > will get
>> >
>> > # ./xgcc -B./  /tmp/x.c -fuse-ld=gold -v
>> > ...
>> > ./collect-ld --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -fuse-ld=gold /lib/../lib64/crt1.o /lib/../lib64/crti.o ./crtbegin.o -L. -L/lib/../lib64 -L/usr/lib/../lib64 /tmp/cclVWcGz.o -v -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed ./crtend.o /lib/../lib64/crtn.o
>> > GNU gold (Linux/GNU Binutils 2.23.51.0.7.20121127) 1.11
>> > /usr/local/bin/ld.gold: fatal error: -f/--auxiliary may not be used without -shared
>> > collect2: error: ld returned 1 exit status
>> >
>> > This is because we pass everything to ld and ld.bfd/ld.gold doesn't
>> > understand -fuse-ld=bfd/-fuse-ld=gold.  It isn't a problem for collect2
>> > since it will filter-out -fuse-ld=bfd/-fuse-ld=gold.  I will submit a
>> > binutils patch to ignore -fuse-ld=bfd/-fuse-ld=gold, similar to -flto
>> > options.
>> >
>> > OK to install?
>>
>> Do we need to consider GNU ld and gold coming from different binutils versions
>> and thus do we need two sets of linker feature tests at configure
>> time?  Eventually
>> also if GNU ld and gold are not in feature-parity for the same binutils version?

This is no different from run-time linker vs configure-time linker.
If it is a link-time failure, we can check:

[hjl@gnu-6 tmp]$ gcc x.o -v -Wl,-v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.7.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap
--enable-shared --enable-threads=posix --enable-checking=release
--disable-build-with-cxx --disable-build-poststage1-with-cxx
--with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto
--enable-plugin --enable-initfini-array --enable-java-awt=gtk
--disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic
--with-arch_32=i686 --with-multilib-list=m32,m64,mx32
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.7.2 20120921 (Red Hat 4.7.2-2) (GCC)
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/4.7.2/:/usr/libexec/gcc/x86_64-redhat-linux/4.7.2/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/4.7.2/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/4.7.2/:/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.7.2/collect2 --build-id
--no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64
-dynamic-linker /lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../.. x.o -v -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/x86_64-redhat-linux/4.7.2/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crtn.o
collect2 version 4.7.2 20120921 (Red Hat 4.7.2-2)
/usr/local/bin/ld --build-id --no-add-needed --eh-frame-hdr
--hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../.. x.o -v -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/x86_64-redhat-linux/4.7.2/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../lib64/crtn.o
GNU ld (GNU Binutils) 2.23.51.20121128
[hjl@gnu-6 tmp]$

>> That is, isn't this going to create hard to debug issues for users?

User uses it by choice. You can check which linker is used.

> Additionally, what is the rationale for this patch? IOW why isn't the following
> enough?
>
> x4 ~ # ln -f /usr/x86_64-pc-linux-gnu/binutils-bin/git/ld.gold  /usr/x86_64-pc-linux-gnu/binutils-bin/git/ld
> x4 ~ # ld -v
> GNU gold (GNU Binutils 2.23.51.20121126) 1.11
> x4 ~ # ln -f /usr/x86_64-pc-linux-gnu/binutils-bin/git/ld.bfd  /usr/x86_64-pc-linux-gnu/binutils-bin/git/ld
> x4 ~ # ld -v
> GNU ld (GNU Binutils) 2.23.51.20121126
>
> Or is this meant as a temporary workaround hack for gold bugs?
>

Yes, it is used as a temporary workaround for linker bugs.

---
H.J.