On 02/27/2017 02:09 PM, Steven Rostedt wrote:

On Mon, 27 Feb 2017 13:41:13 -0800
David Daney [off-list ref] wrote:

quoted

On 02/27/2017 01:06 PM, Steven Rostedt wrote:

quoted

On Mon, 27 Feb 2017 11:59:50 -0800
David Daney [off-list ref] wrote:

quoted

For me the size is not the important issue, it is the alignment of the
struct jump_entry entries in the table.  I don't understand how your
patch helps, and I cannot Acked-by unless I understand what is being
done and can see that it is both correct and necessary.

You brought up a very good point and I'm glad that I had Jason Cc all
the arch maintainers in one patch.

I think jump_labels may be much more broken than we think, and Jason's
fix doesn't fix anything. We had this same issues with tracepoints.

I'm looking at jump_label_init, and how we iterate over an array of
struct jump_entry's that was put together by the linker. The problem is
that jump_entry is not a power of 2 in size.

ELF sections may have an ENTSIZE property exactly for arrays.  Since
each jump_entry will have a unique value they cannot be merged, but we
can tell the assembler they are an array and get them properly packed.
Perhaps something like (untested):

    .pushsection __jump_table,  \"awM\", at progbits,24
    FOO
    .popsection

And the linker will honor this too?

See attached for mips.  It seems to do the right thing.

I leave it as an exercise to the reader to fix the other architectures.

Consult your own  binutils experts to verify that what I say is true.


David Daney
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