linux-kernel - Re: [PATCH 07/12] powerpc/ftrace: FTRACE_WITH

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Message-ID: <20160225151113.GK21932@lst.de>
Date:	Thu, 25 Feb 2016 16:11:13 +0100
From:	Torsten Duwe <duwe@....de>
To:	Balbir Singh <bsingharora@...il.com>
Cc:	Michael Ellerman <mpe@...erman.id.au>, linuxppc-dev@...abs.org,
	pmladek@...e.com, jeyu@...hat.com, jkosina@...e.cz,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	kamalesh@...ux.vnet.ibm.com, live-patching@...r.kernel.org,
	mbenes@...e.cz
Subject: Re: [PATCH 07/12] powerpc/ftrace: FTRACE_WITH_REGS implementation
	for ppc64le

On Thu, Feb 25, 2016 at 11:48:59AM +1100, Balbir Singh wrote:
> > @@ -608,6 +621,9 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> >  					return -ENOENT;
> >  				if (!restore_r2((u32 *)location + 1, me))
> >  					return -ENOEXEC;
> > +				/* Squash the TOC saver for profiler calls */
> > +				if (!strcmp("_mcount", strtab+sym->st_name))
> > +					SQUASH_TOC_SAVE_INSN(value);
> I don't think we need this anymore, do we?

I'm not sure. Once a module is loaded, are all the "bl _mcount"s NOPed out
before any of its functions are run? If not, the _mcount trampoline will
be used, and it must not save R2!

	Torsten