[llvm-dev] RFC: New function attribute "patchable-prologue"="<kind>"

Dean Michael Berris via llvm-dev llvm-dev at lists.llvm.org
Thu Apr 14 06:45:29 PDT 2016

Thanks for looping me in Eric!

If I was going to suggest anything here, I'd like to think about a more
general approach than a very specific attribute like this. My preference is
something like "patchable-function"="kind,kind,..." (if that's even
possible). This allows us to have common infrastructure for being able to
implement different kinds of function-level patching routines at the same
time or even just generalising this mechanism with the instrumentation

It would help probably if I'm able to say more, potentially in the form of
an RFC for what Eric and I are working on. :D


On Thu, Apr 14, 2016 at 6:13 AM Eric Christopher <echristo at gmail.com> wrote:

> On Thu, Apr 7, 2016 at 4:35 PM Sanjoy Das <sanjoy at playingwithpointers.com>
> wrote:
>> Hi Eric,
>> Eric Christopher wrote:
>>  > Two things:
>>  >
>>  > a) I'm not against this
>> Great!
>>  > b) So, what's your use case? I've got something I'm idly working on
>> with
>>  > someone else where we want patchable targets in both prologue and
>>  > epilogue (and some other places...), and am thinking of how to make
>> this
>>  > someone generic enough to build off of there.
>> We plan to use this to be able to divert control flow from an LLVM
>> compiled function to "somewhere else" where the "somewhere else" is
>> usually a differently optimized version of the same function.  One
> Right. So, I've got a use case that I'm working on over here that uses,
> basically, patchable prologue and epilogue and am hoping that this ends up
> being general enough for both.
> I'll take a look at the patch since you've sent it out, but would really
> like to not have to change a lot of how it works. :)
> -eric
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