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From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Nicolai Stange <nstange@suse.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Mimi Zohar <zohar@linux.ibm.com>, Juergen Gross <jgross@suse.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nayna Jain <nayna@linux.ibm.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Joerg Roedel <jroedel@suse.de>,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations
Date: Fri, 10 May 2019 14:14:45 +0200	[thread overview]
Message-ID: <20190510121445.GS2589@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190510122103.5a7bc5416b7af96b27d4fab4@kernel.org>

On Fri, May 10, 2019 at 12:21:03PM +0900, Masami Hiramatsu wrote:
> On Thu, 9 May 2019 13:43:16 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > On Thu, May 09, 2019 at 09:20:06AM -0700, Andy Lutomirski wrote:
> > > > +END(call_to_exception_trampoline)
> > > > --- a/arch/x86/kernel/kprobes/core.c
> > > > +++ b/arch/x86/kernel/kprobes/core.c
> > > > @@ -731,29 +731,8 @@ asm(
> > > >    ".global kretprobe_trampoline\n"
> > > >    ".type kretprobe_trampoline, @function\n"
> > > >    "kretprobe_trampoline:\n"
> > > > -    /* We don't bother saving the ss register */
> > > > -#ifdef CONFIG_X86_64
> > > > -    "    pushq %rsp\n"
> > > > -    "    pushfq\n"
> > > > -    SAVE_REGS_STRING
> > > > -    "    movq %rsp, %rdi\n"
> > > > -    "    call trampoline_handler\n"
> > > > -    /* Replace saved sp with true return address. */
> > > > -    "    movq %rax, 19*8(%rsp)\n"
> > > > -    RESTORE_REGS_STRING
> > > > -    "    popfq\n"
> > > > -#else
> > > > -    "    pushl %esp\n"
> > > > -    "    pushfl\n"
> > > > -    SAVE_REGS_STRING
> > > > -    "    movl %esp, %eax\n"
> > > > -    "    call trampoline_handler\n"
> > > > -    /* Replace saved sp with true return address. */
> > > > -    "    movl %eax, 15*4(%esp)\n"
> > > > -    RESTORE_REGS_STRING
> > > > -    "    popfl\n"
> > > > -#endif
> > > > -    "    ret\n"
> > > > +    "push trampoline_handler\n"
> > > > +    "jmp call_to_exception_trampoline\n"
> > > >    ".size kretprobe_trampoline, .-kretprobe_trampoline\n"
> > > > );
> > > 
> > > 
> > > Potentially minor nit: you’re doing popfl, but you’re not doing TRACE_IRQ_whatever.  This makes me think that you should either add the tracing (ugh!) or you should maybe just skip the popfl.
> > 
> > 
> > Note, kprobes (and ftrace for that matter) are not saving flags for
> > interrupts, but because it must not modify the sign, zero and carry flags.

Uh, C ABI considers those clobbered over function calls, surely. Relying
on those flags over a CALL would be _insane_.

  reply	other threads:[~2019-05-10 12:15 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08  7:49 [PATCH 0/4] x86: int3 fallout Peter Zijlstra
2019-05-08  7:49 ` [PATCH 1/4] x86/entry/32: Clean up return from interrupt preemption path Peter Zijlstra
2019-05-08  7:49 ` [PATCH 2/4] x86/kprobes: Fix frame pointer annotations Peter Zijlstra
2019-05-08 11:54   ` Josh Poimboeuf
2019-05-08 12:04     ` Peter Zijlstra
2019-05-08 12:40       ` Peter Zijlstra
2019-05-08 12:42       ` Josh Poimboeuf
2019-05-08 15:39         ` Peter Zijlstra
2019-05-08 18:48           ` Josh Poimboeuf
2019-05-09  1:20             ` Masami Hiramatsu
2019-05-09  8:14               ` Peter Zijlstra
2019-05-09  9:27                 ` Peter Zijlstra
2019-05-09 14:00                 ` Josh Poimboeuf
2019-05-09 14:01                 ` Masami Hiramatsu
2019-05-09 17:14                   ` Peter Zijlstra
2019-05-10  4:58                     ` Masami Hiramatsu
2019-05-10 12:31                       ` Peter Zijlstra
2019-05-11  0:52                         ` Masami Hiramatsu
2019-05-10 12:40                       ` Peter Zijlstra
2019-05-11  0:56                         ` Masami Hiramatsu
2019-05-13  8:15                           ` Peter Zijlstra
2019-05-09 16:20                 ` Andy Lutomirski
2019-05-09 17:18                   ` Peter Zijlstra
2019-05-09 17:43                   ` Steven Rostedt
2019-05-10  3:21                     ` Masami Hiramatsu
2019-05-10 12:14                       ` Peter Zijlstra [this message]
2019-05-10 12:17                       ` Peter Zijlstra
2019-05-10 14:54                         ` Steven Rostedt
2019-05-09 17:37                 ` Steven Rostedt
2019-05-09 18:26                   ` Peter Zijlstra
2019-05-09 18:36                     ` Steven Rostedt
2019-05-08  7:49 ` [PATCH 3/4] x86/ftrace: Add pt_regs frame annotations Peter Zijlstra
2019-05-08  7:49 ` [RFC][PATCH 4/4] x86_32: Provide consistent pt_regs Peter Zijlstra
2019-05-08 11:57   ` Josh Poimboeuf
2019-05-08 12:46     ` Ingo Molnar
2019-05-08 20:58   ` Linus Torvalds

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