as: How to determine the section of symbols

H.J. Lu hjl.tools@gmail.com
Thu Jul 18 20:39:00 GMT 2019


On Thu, Jul 18, 2019 at 4:28 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Jul 16, 2019 at 10:43:27AM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 15, 2019 at 01:10:42PM -0700, H.J. Lu wrote:
>
> > > .d8 is only a hint.  Is that possible to use the new ".nops SIZE" directive
> > > where SIZE can be an expression.
> >
> > The problem appears to be constructing an expression that yields the
> > exact same semantics as jmp. Given that GCC might provide us with a
> > label into another section, we cannot (per the above as documentation)
> > compute a displacement. Or ever detect this case.
>
> Would it be possible to implement a new mnemonic "nopjmp" that acts the
> exact same as "jmp" but emits either nop2/nop5 instead of actual jumps?
>
> Then I'll need to change the kernel to read the instruction to determine
> size, but at least the nops and jmps would be consistently sized.

How much reduction in kernel size does it provide?  Do you have a small real
usage example in assembly code?

-- 
H.J.



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