as: How to determine the section of symbols

Peter Zijlstra peterz@infradead.org
Thu Jul 18 11:28:00 GMT 2019


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.



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