linux-kernel - Re: [PATCH v8 4/8] ppc64 ftrace_with

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Message-ID: <20160215222111.GA3321@lst.de>
Date:	Mon, 15 Feb 2016 23:21:11 +0100
From:	Torsten Duwe <duwe@....de>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	Balbir Singh <bsingharora@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	Petr Mladek <pmladek@...e.com>, Jessica Yu <jeyu@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org
Subject: Re: [PATCH v8 4/8] ppc64 ftrace_with_regs configuration variables

On Mon, Feb 15, 2016 at 03:04:08PM +0100, Torsten Duwe wrote:
> If you use "-pg -mprofile-kernel", gcc seems to forget that, and omits the TOC
> load, for a similar assembler calling sequence.
> 
> Looking at the code I can _understand_ why this is so, but my GCC knowledge
> is not that deep that I could easily _fix_ this reliably.

Nonetheless, here's a proposal.

--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -25154,6 +25154,10 @@ rs6000_emit_prologue (void)
     {
       cfun->machine->r2_setup_needed = df_regs_ever_live_p (TOC_REGNUM);
 
+      /* Profiling _will_ generate a call to a global _mcount. */
+      if (crtl->profile)
+	cfun->machine->r2_setup_needed = true;
+
       /* With -mminimal-toc we may generate an extra use of r2 below.  */
       if (TARGET_TOC && TARGET_MINIMAL_TOC && get_pool_size () != 0)
 	cfun->machine->r2_setup_needed = true;