Messages in this thread | | | From | Ard Biesheuvel <> | Date | Tue, 15 Nov 2016 19:25:12 +0000 | Subject | Re: [PATCH/RESEND] recordmcount: arm: Implement make_nop |
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On 15 November 2016 at 19:18, Stephen Boyd <sboyd@codeaurora.org> wrote: > 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? >
Yes. But that implies then that you should not be using big-endian instruction encodings at all, and simply use the _le variants for both LE and BE8
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