Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes

[Steven Rostedt]

On Mon, 27 Feb 2017 13:41:13 -0800
David Daney <ddaney@xxxxxxxxxxxxxxxxxx> wrote:

> On 02/27/2017 01:06 PM, Steven Rostedt wrote:
> > On Mon, 27 Feb 2017 11:59:50 -0800
> > David Daney <ddaney@xxxxxxxxxxxxxxxxxx> wrote:
> >  
> >> 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\",@progbits,24
>     FOO
>     .popsection
> 

And the linker will honor this too?

-- Steve