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    SubjectRe: [PATCHSET x86/master] add stack protector support for x86_32

    * Tejun Heo <tj@kernel.org> wrote:

    > Ingo Molnar wrote:
    > > * Ingo Molnar <mingo@elte.hu> wrote:
    > >
    > >> [...] I might not get around testing it today and pushing it out into tip:master,
    > >> but i pushed out the core/percpu bits, should you queue up further changes.
    > >
    > > ok, activated it for -tip testing, and there's a 64-bit build failure caused by
    > > it:
    > >
    > > arch/x86/kernel/head64.o: In function `x86_64_start_reservations':
    > > head64.c:(.init.text+0x26): undefined reference to `__stack_chk_guard'
    > > head64.c:(.init.text+0xc2): undefined reference to `__stack_chk_guard'
    > > arch/x86/kernel/head64.o: In function `x86_64_start_kernel':
    > > head64.c:(.init.text+0x104): undefined reference to `__stack_chk_guard'
    > > head64.c:(.init.text+0x1cd): undefined reference to `__stack_chk_guard'
    > > arch/x86/kernel/head.o: In function `reserve_ebda_region':
    > > head.c:(.init.text+0xb): undefined reference to `__stack_chk_guard'
    > > arch/x86/kernel/head.o:head.c:(.init.text+0x87): more undefined references to
    > > `__stack_chk_guard' follow
    >
    > Call to __stack_chk_guard is probably generated automatically.
    > Strangely, my gcc only generates calls to __stack_chk_fail.
    >
    > > gcc --version
    > gcc (SUSE Linux) 4.3.2 [gcc-4_3-branch revision 141291]
    > Copyright (C) 2008 Free Software Foundation, Inc.
    > This is free software; see the source for copying conditions. There is NO
    > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    > > nm build/vmlinux|grep __stack_chk_
    > 00000000f0fdf6cb A __crc___stack_chk_fail
    > ffffffff80d53e50 r __kcrctab___stack_chk_fail
    > ffffffff80d5ff81 r __kstrtab___stack_chk_fail
    > ffffffff80d3d140 r __ksymtab___stack_chk_fail
    > ffffffff80248619 T __stack_chk_fail
    >
    > I'll try other compilers but which version are you using? The
    > difference is that before the patchset, -fno-stack-protector was
    > always added whether stackprotector was enabled or not so this problem
    > wasn't visible (at the cost of bogus stackprotector of course). We'll
    > probably need to add __stack_chk_guard or disable if gcc generates
    > such symbol. I'll play with different gccs.

    that was with a crosscompiler:

    aldebaran:~> /opt/crosstool/gcc-4.2.3-glibc-2.3.6/x86_64-unknown-linux-gnu/bin/x86_64-unknown-linux-gnu-gcc -v
    Using built-in specs.
    Target: x86_64-unknown-linux-gnu
    Configured with:
    /home/mingo/s/crosstool-0.43/build/x86_64-unknown-linux-gnu/gcc-4.2.3-glibc-2.3.6/gcc-4.2.3/configure
    --target=x86_64-unknown-linux-gnu --host=i686-host_pc-linux-gnu
    --prefix=/opt/crosstool/gcc-4.2.3-glibc-2.3.6/x86_64-unknown-linux-gnu
    --disable-multilib
    --with-sysroot=/opt/crosstool/gcc-4.2.3-glibc-2.3.6/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sys-root
    --with-local-prefix=/opt/crosstool/gcc-4.2.3-glibc-2.3.6/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sys-root
    --disable-nls --enable-threads=posix --enable-symvers=gnu --enable-__cxa_atexit
    --enable-languages=c --enable-shared --enable-c99 --enable-long-long
    Thread model: posix
    gcc version 4.2.3

    The problem is i think GCC's brain-dead stackprotector support - having different
    models for user-space and kernel-space stackprotector. So this compiler is not
    _able_ to actually build a stackprotector kernel - but we should auto-discover that.

    Ingo


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