Re: using mprotect to write to .text

[David Daney <david.daney@cavium.com>]

On 10/11/2011 10:31 AM, Joe Buehler wrote:
> David Daney wrote:
>
>> No, it does nothing of the sort.  You need cacheflush() for that.
>
> OK, I looked at cacheflush and it can be used to flush the icache on all
> CPUs, which is what I want.  My current code sequence is more than that
> however.  Something like this:
>
> 	CVMX_ICACHE_INVALIDATE;

This only works if you can guarantee that the code will never be run on 
a different CPU than the current one.  For most Linux code you cannot 
make such an assertion.

> 	CVMX_SYNC;

Unneeded.

> 	uint64_t tmp;
> 	asm volatile ("    la %0,10f\n"
> 		  "    jr.hb %0\n"
> 		  "    nop\n"
> 		  "    10:\n" : "=r" (tmp) : : "memory");

jr.hb is equivalent to jr on Octeon.

>
> I can certainly modify cacheflush for my application so the extra hazard
> clearing is done when icache is flushed.  Is there any way to avoid that
> and use existing kernel functionality?
>

I cannot parse the meaning out of these last two sentences.  The 
cacheflush() system call both exists and works.  You want to change it?

David Daney