lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 12 Mar 2009 23:34:01 -0400 (EDT) From: Steven Rostedt <rostedt@...dmis.org> To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, Frederic Weisbecker <fweisbec@...il.com>, Lai Jiangshan <laijs@...fujitsu.com>, Steven Rostedt <srostedt@...hat.com> Subject: Re: [PATCH 08/16] tracing: have event_trace_printk use static tracer On Fri, 13 Mar 2009, KOSAKI Motohiro wrote: > > > > +#define event_trace_printk(ip, fmt, args...) \ > > > > +do { \ > > > > + __trace_printk_check_format(fmt, ##args); \ > > > > + tracing_record_cmdline(current); \ > > > > + if (__builtin_constant_p(fmt)) { \ > > > > + static const char *trace_printk_fmt \ > > > > + __attribute__((section("__trace_printk_fmt"))) = \ > > > > + __builtin_constant_p(fmt) ? fmt : NULL; \ > > > > > > Why __builtin_constant_p(fmt) evaluate twice? > > > > It's explained in another patch. But this was a real PITA. We first tried > > this with just the "if (__builtin_return_p(fmt))" but the way gcc works, > > it handles the global data assignments before optimizing out condition > > logic. Thus we ended up getting errors about can not initialize static > > variable with a non constant. > > > > But the ? : operation of the assignment is optimized before the assignment > > is made. Thus, if fmt is not constant, then we avoid this warning. Then > > during the conditional optimization, gcc will remove that part of the code > > altogether. > > > > Thus the double __builtin_constant_p(fmt) is needed twice. Try taking out > > one of them and see what happens with: > > > > myfunc(const char *fmt) { > > > > event_trace_printk(fmt); > > > > } > > > > Of course the way this is made, we may not call it that way, but I wanted > > to be safe. > > Thanks for kindful explain. > So, I guess many developer feel it's strange. > adding comment is better? Yeah, I cut and pasted this out from the trace_printk in kernel.h where I had the comment there. But I think you are right, I probably should copy that comment here too. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists