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    SubjectRe: [committed, PATCH] Add -mshared option to x86 ELF assembler

    * Andy Lutomirski <luto@amacapital.net> wrote:

    > On Mon, Jun 1, 2015 at 4:05 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
    > > On Mon, Jun 1, 2015 at 1:32 AM, Markus Trippelsdorf
    > > <markus@trippelsdorf.de> wrote:
    > >> On 2015.05.15 at 03:34 -0700, H.J. Lu wrote:
    > >>> This patch adds -mshared option to x86 ELF assembler. By default,
    > >>> assembler will optimize out non-PLT relocations against defined non-weak
    > >>> global branch targets with default visibility. The -mshared option tells
    > >>> the assembler to generate code which may go into a shared library
    > >>> where all non-weak global branch targets with default visibility can
    > >>> be preempted. The resulting code is slightly bigger. This option
    > >>> only affects the handling of branch instructions.
    > >>>
    > >>> This Linux kernel patch is needed to create a working x86 Linux kernel if
    > >>> it hasn't been applied:
    > >>>
    > >>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
    > >>> index ae6588b..b91a00c 100644
    > >>> --- a/arch/x86/kernel/head_64.S
    > >>> +++ b/arch/x86/kernel/head_64.S
    > >>> @@ -339,8 +339,8 @@ early_idt_handlers:
    > >>> i = i + 1
    > >>> .endr
    > >>>
    > >>> -/* This is global to keep gas from relaxing the jumps */
    > >>> -ENTRY(early_idt_handler)
    > >>> +/* This is weak to keep gas from relaxing the jumps */
    > >>> +WEAK(early_idt_handler)
    > >>> cld
    > >>
    > >> Have you posted the patch to LKML already?
    > >> (I hit this issue today and it took me a while to figure out the cause.)
    > >
    > > A kernel patch will be checked in soon.
    > >
    >
    > It already is:
    >
    > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=x86/asm&id=cdeb6048940fa4bfb429e2f1cba0d28a11e20cd5
    >
    > It's currently queued for 4.2.
    >
    > Ingo, would it make sense to promote this to 4.1? It's definitely a violation
    > of the "no development after the merge window" rule, but it's sort of a build
    > fix. [...]

    Yeah, agreed - the commit was problem-free in testing, so I've cherry-picked it
    over into tip:x86/urgent and will push it to Linus for v4.1.

    Thanks,

    Ingo


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