lkml.org 
[lkml]   [2008]   [Apr]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 1/2] Marker probes in futex.c

* Arjan van de Ven <arjan@infradead.org> wrote:

> > Not only does the compare and jmp need to be consecutive, but the
> > movb $0x0,%al also does. I *could* try to detect specific code
> > inserted in between, but I really have to make sure I don't get
> > burned by the compiler inserting a jmp there.
>
> I wonder if just sticking in 2 barriers around your code make gcc stop
> moving stuff too much

hm, an extra optimization barrier might have worse effects than even an
extra instruction. I think if the detection and patching can be made
100% safe, we dont care about the remaining 4% of markers that gcc
somehow reorders.

and in parallel gcc folks might want to start helping us achieve
single-instruction branch points? Currently there's no way to get flags
values out of inline assembly, except via a register intermediary which
adds another instruction. For flags that are unaffected by gcc's
input/output constraint generation code it would make sense to allow
them to be exported out of inline assembly.

Ingo


\
 
 \ /
  Last update: 2008-04-16 16:33    [W:0.106 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site