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Date: Thu, 25 Feb 2016 14:52:05 +0100 From: Torsten Duwe <duwe@....de> To: Michael Ellerman <mpe@...erman.id.au> Cc: linuxppc-dev@...abs.org, bsingharora@...il.com, linux-kernel@...r.kernel.org, rostedt@...dmis.org, kamalesh@...ux.vnet.ibm.com, pmladek@...e.com, jeyu@...hat.com, jkosina@...e.cz, live-patching@...r.kernel.org, mbenes@...e.cz Subject: Re: [PATCH 04/12] powerpc/ftrace: Prepare for -mprofile-kernel On Thu, Feb 25, 2016 at 01:28:27AM +1100, Michael Ellerman wrote: > @@ -450,17 +448,44 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs, > return (unsigned long)&stubs[i]; > } > > +#ifdef CC_USING_MPROFILE_KERNEL > +static int is_early_mcount_callsite(u32 *instruction) > +{ > + /* -mprofile-kernel sequence starting with > + * mflr r0 and maybe std r0, LRSAVE(r1). > + */ > + if ((instruction[-3] == PPC_INST_MFLR && > + instruction[-2] == PPC_INST_STD_LR) || > + instruction[-2] == PPC_INST_MFLR) { > + /* Nothing to be done here, it's an _mcount > + * call location and r2 will have to be > + * restored in the _mcount function. > + */ > + return 1; > + } > + return 0; > +} > +#else *You* said this might page fault :) Did we agree yet whether we insist on a streamlined compiler? (GCC commit e95d0248dace required)? If not: if (instruction[-2] == PPC_INST_STD_LR) { if (instruction[-3] == PPC_INST_MFLR) return 1; } else if (instruction[-2] == PPC_INST_MFLR) return 1; return 0; leaves less freedom for the compiler to "optimise". Signed-off-by: Torsten Duwe <duwe@...e.de> Torsten
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