From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
Shuah Khan <shuah@kernel.org>,
Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH] tracing/selftests: Ignore __pfx_ symbols in kprobe test
Date: Fri, 10 Feb 2023 10:51:00 +0100 [thread overview]
Message-ID: <Y+YThNzVa1ECIuYM@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230209232305.672dd0249e0db41552b28763@kernel.org>
On Thu, Feb 09, 2023 at 11:23:05PM +0900, Masami Hiramatsu wrote:
> BTW, currently kprobe event rejects this __pfx_ symbols because it is notrace
> symbols, thus we can trace it if CONFIG_KPROBE_EVENTS_ON_NOTRACE=y.
> But I guess it should not probe that place always because it should never
> executed right?
Execution can take place in those ranges when X86_FEATURE_CALL_DEPTH is
enabled or when CONFIG_KCFI && X86_FEATURE_IBT.
In the first of those cases the prefix bytes are filled with call
accounting instructions and every direct call to $sym is patched to
point to __pfx_$sym+6 (aka $sym-10).
https://lore.kernel.org/all/20220915111039.092790446@infradead.org/
In the second case (FineIBT) it is probably easiest if you look at the
comment in arch/x86/kernel/alternative.c near CONFIG_FINEIBT.
https://lore.kernel.org/all/20221027092812.185993858@infradead.org/
The __pfx_ and __cfi_ symbols are the same (in fact, when
CONFIG_CFI_CLANG=y the compiler generates them and objtool no longer
emits the __pfx_ symbols).
https://lore.kernel.org/all/20221028194453.592512209@infradead.org/
next prev parent reply other threads:[~2023-02-10 9:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 18:51 [PATCH] tracing/selftests: Ignore __pfx_ symbols in kprobe test Steven Rostedt
2023-02-07 18:54 ` Steven Rostedt
2023-02-08 18:05 ` Peter Zijlstra
2023-02-08 22:03 ` Steven Rostedt
2023-02-09 10:45 ` Peter Zijlstra
2023-02-09 14:23 ` Masami Hiramatsu
2023-02-10 9:51 ` Peter Zijlstra [this message]
2023-02-09 14:06 ` Masami Hiramatsu
2023-02-14 1:46 ` Steven Rostedt
2023-03-18 18:42 ` Steven Rostedt
2023-03-20 12:56 ` Shuah Khan
2023-03-20 16:30 ` Shuah Khan
2023-03-20 16:32 ` Steven Rostedt
2023-03-20 16:40 ` Steven Rostedt
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