Re: [patch V4 part 1 20/36] vmlinux.lds.h: Create section for protection against instrumentation

Thomas Gleixner
2020-05-06T17:06:19Z

Peter Zijlstra <peterz@infradead.org> writes:
> On Wed, May 06, 2020 at 09:08:31AM -0700, Sean Christopherson wrote:
>> On Tue, May 05, 2020 at 03:16:22PM +0200, Thomas Gleixner wrote:
>> > Provide also a set of markers: instr_begin()/end()
>> >
>> > These are used to mark code inside a noinstr function which calls
>> > into regular instrumentable text section as safe.
>>
>> ...
>>
>> > --- a/include/linux/compiler.h
>> > +++ b/include/linux/compiler.h
>> > @@ -120,10 +120,27 @@ void ftrace_likely_update(struct ftrace_
>> > /* Annotate a C jump table to allow objtool to follow the code flow */
>> > #define __annotate_jump_table __section(.rodata..c_jump_table)
>> >
>> > +/* Begin/end of an instrumentation safe region */
>> > +#define instr_begin() ({ \
>> > + asm volatile("%c0:\n\t" \
>> > + ".pushsection .discard.instr_begin\n\t" \
>> > + ".long %c0b - .\n\t" \
>> > + ".popsection\n\t" : : "i" (__COUNTER__)); \
>> > +})
>> > +
>> > +#define instr_end() ({ \
>> > + asm volatile("%c0:\n\t" \
>> > + ".pushsection .discard.instr_end\n\t" \
>> > + ".long %c0b - .\n\t" \
>> > + ".popsection\n\t" : : "i" (__COUNTER__)); \
>> > +})
>>
>> Any chance we could spell these out, i.e. instrumentation_begin/end()? I
>> can't help but read these as "instruction_begin/end". At a glance, the
>> long names shouldn't cause any wrap/indentation issues.
>
> The kernel naming convention is insn for instruction, not instr. That
> said, you're not the first to be confused by this.

I'm happy to spell it out. Was just lazy I guess.