[Bug libstdc++/35816] New: libstdc++ built during bootstrap is pulling in host g++ support for atomic builtins

[Bug libstdc++/35816] New: libstdc++ built during bootstrap is pulling in host g++ support for atomic builtins

[oblivian at users dot sourceforge dot net]

When compiling a combined gcc + g++ + binutils, the configure script for the
libstdc++ library is using the host g++ rather than the last stage g++ for
determining atomic builtin support status.

While I probably need to compile the toolchain with CXXFLAGS=-march=i486, from
what I've read, to enable support for atomic builtins in the compiler, I did
not.  This resulted in a target g++ that did not support atomic builtins and a
libstdc++ that expected the compiler did because it got the value from checking
the host g++ rather than the final bootstrap stage g++.

The configure parameters were:
  --prefix=/$(TOOLS_DIR)/usr \
  --with-sysroot=/$(TOOLS_DIR) \
  --with-pic \
  --enable-shared \
  --enable-clocale=gnu \
  --enable-threads=posix \
  --enable-__cxa_atexit \
  --enable-languages=c,c++ \
  --enable-checking=release \
  --disable-werror \
  --enable-stage1-checking \
  --enable-bootstrap


-- 
           Summary: libstdc++ built during bootstrap is pulling in host g++
                    support for atomic builtins
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: oblivian at users dot sourceforge dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ built during bootstrap is pulling in host g++ support for atomic builtins

[oblivian at users dot sourceforge dot net]

------- Comment #1 from oblivian at users dot sourceforge dot net  2008-04-03 17:34 -------
After looking back at my 4.2.3 build logs.  The above is somewhat incorrect. 
In 4.2.3, the pass 2 toolchain build of libstdc++ correctly checked the target
g++ rather than the host and reported that it would not use atomic builtins. 
It appears that this has changed in 4.3.0 or is an artifact of using sysroot
(which should not look at the host g++ for configuration options).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ build during bootstrap is optimizing away atomic builtin check

[oblivian at users dot sourceforge dot net]

------- Comment #2 from oblivian at users dot sourceforge dot net  2008-04-03 20:45 -------
Ok so the gcc/g++ i build has optimization on by default. The configuration
scripts don't seem to take this into account and the call to CXX for the atomic
check is optimizing away the check in the output assembly code; thus, the grep
for __sync_fetch_and_add fails and does not turn off atomic builtins.  

the following is right before the code generation in the configure file
  # Fake what AC_TRY_COMPILE does.  XXX Look at redoing this new-style.

The check probably needs to also take into account optimization so that the
check for __sync_fetch_and_add can not be removed regardless of optimization
flags.

To revert to 4.2.3 behavior I inserted a -O0 in the ac_compile command for the
check.


-- 

oblivian at users dot sourceforge dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|libstdc++ built during      |libstdc++ build during
                   |bootstrap is pulling in host|bootstrap is optimizing away
                   |g++ support for atomic      |atomic builtin check
                   |builtins                    |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ build during bootstrap is optimizing away atomic builtin check

[bkoz at gcc dot gnu dot org]

------- Comment #3 from bkoz at gcc dot gnu dot org  2008-04-14 22:48 -------

Wow. Confirmed. This does not happen at -O2 with gcc-4.1.2

However, on gcc-4.3.0 branch:

$bld/H-x86-gcc-4_3-branch.20080227/bin/g++ -O2 -S -march=i386 testatomic.cc

gives:

        .file   "testatomic.cc"
        .text
        .p2align 2,,3
.globl main
        .type   main, @function
main:
.LFB2:
        leal    4(%esp), %ecx
.LCFI0:
        andl    $-16, %esp
        pushl   -4(%ecx)
.LCFI1:
        pushl   %ebp
.LCFI2:
        movl    %esp, %ebp
.LCFI3:
        pushl   %ecx
.LCFI4:
        subl    $16, %esp
.LCFI5:
        leal    -8(%ebp), %edx
        xorl    %eax, %eax
        lock addl       %eax, (%edx)
        addl    $16, %esp
        popl    %ecx
        leave
        leal    -4(%ecx), %esp
        ret
.LFE2:
        .size   main, .-main
        .ident  "GCC: (GNU) 4.3.0 20080227 (prerelease)"
        .section        .note.GNU-stack,"",@progbits


Fix in progress.


-- 

bkoz at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |bkoz at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-04-14 22:48:43
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ build during bootstrap is optimizing away atomic builtin check

[bkoz at gcc dot gnu dot org]

------- Comment #4 from bkoz at gcc dot gnu dot org  2008-04-14 23:54 -------
Subject: Bug 35816

Author: bkoz
Date: Mon Apr 14 23:53:15 2008
New Revision: 134297

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=134297
Log:
2008-04-14  Benjamin Kosnik  <bkoz@redhat.com>

        PR libstdc++/35816
        * acinclude.m4 (GLIBCXX_ENABLE_ATOMIC_BUILTINS): Set CXXFLAGS to
        -O0 when checking for atomic builtins.
        * configure: Regenerate.


Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/acinclude.m4
    trunk/libstdc++-v3/configure


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ build during bootstrap is optimizing away atomic builtin check

[bkoz at gcc dot gnu dot org]

------- Comment #6 from bkoz at gcc dot gnu dot org  2008-04-15 00:26 -------

fixed in trunk and on gcc-4_3-branch


-- 

bkoz at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816

[Bug libstdc++/35816] libstdc++ build during bootstrap is optimizing away atomic builtin check

[bkoz at gcc dot gnu dot org]

------- Comment #5 from bkoz at gcc dot gnu dot org  2008-04-15 00:26 -------
Subject: Bug 35816

Author: bkoz
Date: Tue Apr 15 00:25:45 2008
New Revision: 134305

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=134305
Log:
2008-04-14  Benjamin Kosnik  <bkoz@redhat.com>

        PR libstdc++/35816
        * acinclude.m4 (GLIBCXX_ENABLE_ATOMIC_BUILTINS): Set CXXFLAGS to
        -O0 when checking for atomic builtins.
        * configure: Regenerate.



Modified:
    branches/gcc-4_3-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_3-branch/libstdc++-v3/acinclude.m4
    branches/gcc-4_3-branch/libstdc++-v3/configure


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35816