[Bug lto/49286] New: LTO incompatible with PIC and inline asm

[Bug lto/49286] New: LTO incompatible with PIC and inline asm

[emil.langrock at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49286

           Summary: LTO incompatible with PIC and inline asm
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: emil.langrock@gmx.de


Created attachment 24435
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24435
Minimal example

I have a library which needs to be compiled as PIC (amd64). It has different
parts which cannot be written in C and thus uses inline assembly. Other parts
can benefit extremely by using LTO (~10% faster and ~10% size reduction). By
default it is compiled using something like that:


$ gcc -g -O2 -fPIC -DPIC -o test.o -c test.c
$ gcc -fPIC -shared test.o -o test.so

This works perfectly. It will produce an PIC error when compiling it with LTO:


$ gcc -flto -g -O2 -fPIC -DPIC -o test.o -c test.c
$ gcc -flto -g -O2 -fPIC -DPIC -shared test.o -o test.so
/usr/bin/ld: /tmp/ccMYQCew.ltrans0.ltrans.o: relocation R_X86_64_PC32 against
undefined symbol `evil_long' can not be used when making a shared object;
recompile with -fPIC
/usr/bin/ld: final link failed: Bad value
collect2: ld returned 1 exit status


To the version I use:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.0-11'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-multiarch
--with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc
--with-arch-32=i586 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 20110604 (prerelease) (Debian 4.6.0-11) 
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/:/usr/lib/gcc/x86_64-linux-gnu/4.6.1/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.6.1/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/:/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/4.6.1/collect2 --build-id --no-add-needed
--eh-frame-hdr -m elf_x86_64 --hash-style=both -dynamic-linker
/lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crti.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtbegin.o
-L/usr/lib/gcc/x86_64-linux-gnu/4.6.1
-L/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../.. --version
-lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crtn.o
collect2 version 4.6.1 20110604 (prerelease) (x86-64 Linux/ELF)
/usr/bin/ld --build-id --no-add-needed --eh-frame-hdr -m elf_x86_64
--hash-style=both -dynamic-linker /lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crti.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtbegin.o
-L/usr/lib/gcc/x86_64-linux-gnu/4.6.1
-L/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../.. --version
-lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../../lib/crtn.o
GNU ld (GNU Binutils for Debian) 2.21.51.20110523
Copyright 2011 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty

Re: [Bug lto/49286] New: LTO incompatible with PIC and inline asm

[Jan Hubicka]

The problem is that GCC do not see that evil_long is used by the asm statement.
Static variables are renamed (in order to produce single .s file you can't have
two different statics with the same name) and then the problem is misdiagnozed
as external reference.

Make evil_long as output of the asm. I.e. something like
asm volatile ("mov %%rsp, $1"::"=m"(evil_long));

All variables accessed by asm statements in direct way (that is w/o the constraints)
must be public and decorated with __attribute__ ((externally_visible))

Honza

[Bug lto/49286] LTO incompatible with PIC and inline asm

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49286

--- Comment #1 from Jan Hubicka <hubicka at ucw dot cz> 2011-06-05 11:55:22 UTC ---
The problem is that GCC do not see that evil_long is used by the asm statement.
Static variables are renamed (in order to produce single .s file you can't have
two different statics with the same name) and then the problem is misdiagnozed
as external reference.

Make evil_long as output of the asm. I.e. something like
asm volatile ("mov %%rsp, $1"::"=m"(evil_long));

All variables accessed by asm statements in direct way (that is w/o the
constraints)
must be public and decorated with __attribute__ ((externally_visible))

Honza

[Bug lto/49286] LTO incompatible with PIC and inline asm

[emil.langrock at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49286

Emil Langrock <emil.langrock at gmx dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #2 from Emil Langrock <emil.langrock at gmx dot de> 2011-06-05 11:59:24 UTC ---
Ok, thanks for the explanation. Sounds reasonable and makes this bug report
invalid

[Bug lto/49286] LTO incompatible with PIC and inline asm

[emil.langrock at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49286

--- Comment #3 from Emil Langrock <emil.langrock at gmx dot de> 2011-06-05 13:50:31 UTC ---
Created attachment 24436
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24436
Minimal example with fix