Messages in this thread | | | Date | Tue, 15 Nov 2016 11:18:07 -0800 | From | Stephen Boyd <> | Subject | Re: [PATCH/RESEND] recordmcount: arm: Implement make_nop |
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On 11/15, Ard Biesheuvel wrote: > On 19 October 2016 at 00:42, Stephen Boyd <sboyd@codeaurora.org> wrote: > > In similar spirit to x86 and arm64 support, add a make_nop_arm() > > to replace calls to mcount with a nop in sections that aren't > > traced. > > > > Cc: Russell King <linux@arm.linux.org.uk> > > Acked-by: Rabin Vincent <rabin@rab.in> > > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> > > --- > > scripts/recordmcount.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 65 insertions(+) > > > > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c > > index 5423a58d1b06..aeb34223167c 100644 > > --- a/scripts/recordmcount.c > > +++ b/scripts/recordmcount.c > > @@ -213,6 +213,59 @@ static int make_nop_x86(void *map, size_t const offset) > > return 0; > > } > > > > +static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */ > > +static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */ > > Shouldn't you be taking the difference between BE8 and BE32 into > account here? IIRC, BE8 uses little endian encoding for instructions.
I admit I haven't tested on a pre-armv6 CPU so I haven't come across the case of a BE32 CPU. But from what I can tell that doesn't matter.
According to scripts/Makefile.build, cmd_record_mcount only runs the recordmcount program if CONFIG_FTRACE_MCOUNT_RECORD=y. That config is defined as:
config FTRACE_MCOUNT_RECORD def_bool y depends on DYNAMIC_FTRACE depends on HAVE_FTRACE_MCOUNT_RECORD
And in arch/arm/Kconfig we see that DYNAMIC_FTRACE is selected:
select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU
which means that FTRACE_MCOUNT_RECORD can't be set when CPU_ENDIAN_BE32 is set.
Do you agree that BE32 is not a concern here?
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