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    SubjectRe: [PATCH 0/2] jump label: update for .39
    On Thu, Mar 10, 2011 at 02:45:29PM -0500, Steven Rostedt wrote:
    > On Thu, 2011-03-10 at 14:25 -0500, Steven Rostedt wrote:
    > > On Thu, 2011-03-10 at 10:57 -0800, David Daney wrote:
    > > > On 03/10/2011 10:53 AM, Steven Rostedt wrote:
    > > > > On Thu, 2011-03-10 at 10:47 -0800, David Daney wrote:
    > > > >
    > > > >> The alignment requested by the assembler will have to satisfy *all* the
    > > > >> requested alignments, so manually forcing everything to .align 8 (or
    > > > >> .align 4 for 32-bit) should ensure that the linker doesn't put in any holes.
    > > > >
    > > > > I would agree with the assessment although, I don't know that it is
    > > > > documented anywhere that this is what happens. As the previous "bug"
    > > > > with the trace_events was solved by me adding .align(4) everywhere, I
    > > > > would think that .align(sizeof(long)) would work here too.
    > > > >
    > > > > It may be a good ideal to force this alignment, and not add wasted
    > > > > space. If anything, if this (hypothetical) bug appears, it will most
    > > > > likely show up as a crash on boot up. I'm not too concerned about it.
    > > > >
    > > >
    > > > If the linker put in gratuitous holes, things like __ex_table would
    > > > break too.
    > >
    > > Again, as I have said (although I said extable not __ex_table), there
    > > seems to be no problem when the data is of a power of 2 as well. As
    > > __ex_table size is a power of 2. We just don't know if the linker will
    > > add holes when the size is something other than power of 2.
    >
    > Anyway, I think the best thing for now is to have Jason add
    > the .align(sizeof(long)) in the inline assembly for all locations and be
    > done with it.
    >

    agreed. something like the following is all that's needed for x86. Sparc
    already has this, so mips just needs something similar. Steve, should I
    re-post the entire series. Or can I just post this patch separately?

    thanks,

    -Jason


    diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
    index f217cee..57f31ff 100644
    --- a/arch/x86/include/asm/jump_label.h
    +++ b/arch/x86/include/asm/jump_label.h
    @@ -8,6 +8,7 @@
    #include <asm/asm.h>

    #define JUMP_LABEL_NOP_SIZE 5
    +#define BYTES_PER_LONG (BITS_PER_LONG / 8)

    #define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"

    @@ -16,9 +17,10 @@ static __always_inline bool arch_static_branch(struct jump_label_key *key)
    asm goto("1:"
    JUMP_LABEL_INITIAL_NOP
    ".pushsection __jump_table, \"aw\" \n\t"
    - _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
    + ".align %c0\n\t"
    + _ASM_PTR "1b, %l[l_yes], %c1 \n\t"
    ".popsection \n\t"
    - : : "i" (key) : : l_yes);
    + : : "i" BYTES_PER_LONG, "i" (key) : : l_yes);
    return false;
    l_yes:
    return true;

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