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From: Michael Ellerman <mpe@ellerman.id.au>
To: Jordan Niethe <jniethe5@gmail.com>, linuxppc-dev@lists.ozlabs.org
Cc: alistair@popple.id.au, npiggin@gmail.com, bala24@linux.ibm.com,
	Jordan Niethe <jniethe5@gmail.com>,
	naveen.n.rao@linux.vnet.ibm.com, dja@axtens.net
Subject: Re: [PATCH v7 04/28] powerpc/xmon: Use bitwise calculations in_breakpoint_table()
Date: Tue, 05 May 2020 17:08:34 +1000	[thread overview]
Message-ID: <871rnyeu4t.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20200501034220.8982-5-jniethe5@gmail.com>

Jordan Niethe <jniethe5@gmail.com> writes:
> A modulo operation is used for calculating the current offset from a
> breakpoint within the breakpoint table. As instruction lengths are
> always a power of 2, this can be replaced with a bitwise 'and'. The
> current check for word alignment can be replaced with checking that the
> lower 2 bits are not set.
>
> Suggested-by: Christophe Leroy <christophe.leroy@c-s.fr>
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
> v6: New to series
> ---
>  arch/powerpc/xmon/xmon.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index bbfea22f4a96..e122f0c8a044 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -857,8 +857,8 @@ static struct bpt *in_breakpoint_table(unsigned long nip, unsigned long *offp)
>  	off = nip - (unsigned long) bpt_table;
>  	if (off >= sizeof(bpt_table))
>  		return NULL;
> -	*offp = off % BPT_SIZE;
> -	if (*offp != 0 && *offp != 4)
> +	*offp = off & (BPT_SIZE - 1);
> +	if (off & 3)
>  		return NULL;

It would be even better if you didn't hard code the 3 wouldn't it?

eg:

+	*offp = off & (BPT_SIZE - 1);
+	if (off & (BPT_SIZE - 1))
 		return NULL;

cheers

  parent reply	other threads:[~2020-05-05  7:10 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-01  3:41 [PATCH v7 00/28] Initial Prefixed Instruction support Jordan Niethe
2020-05-01  3:41 ` [PATCH v7 01/28] powerpc/xmon: Remove store_inst() for patch_instruction() Jordan Niethe
2020-05-01  3:41 ` [PATCH v7 02/28] powerpc/xmon: Move breakpoint instructions to own array Jordan Niethe
2020-05-04  5:41   ` Alistair Popple
2020-05-04  5:52     ` Jordan Niethe
2020-05-01  3:41 ` [PATCH v7 03/28] powerpc/xmon: Move breakpoints to text section Jordan Niethe
2020-05-01  3:41 ` [PATCH v7 04/28] powerpc/xmon: Use bitwise calculations in_breakpoint_table() Jordan Niethe
2020-05-04  5:41   ` Alistair Popple
2020-05-05  7:08   ` Michael Ellerman [this message]
2020-05-05  7:31     ` Jordan Niethe
2020-05-01  3:41 ` [PATCH v7 05/28] powerpc: Change calling convention for create_branch() et. al Jordan Niethe
2020-05-04  2:55   ` Alistair Popple
2020-05-01  3:41 ` [PATCH v7 06/28] powerpc: Use a macro for creating instructions from u32s Jordan Niethe
2020-05-04  5:54   ` Alistair Popple
2020-05-01  3:41 ` [PATCH v7 07/28] powerpc: Use an accessor for instructions Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 08/28] powerpc: Use a function for getting the instruction op code Jordan Niethe
2020-05-04  8:01   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 09/28] powerpc: Use a function for byte swapping instructions Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 10/28] powerpc: Introduce functions for instruction equality Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 11/28] powerpc: Use a datatype for instructions Jordan Niethe
2020-05-02 14:29   ` kbuild test robot
2020-05-02 14:29     ` kbuild test robot
2020-05-01  3:42 ` [PATCH v7 12/28] powerpc: Use a function for reading instructions Jordan Niethe
2020-05-04  8:26   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 13/28] powerpc: Add a probe_user_read_inst() function Jordan Niethe
2020-05-04  8:30   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 14/28] powerpc: Add a probe_kernel_read_inst() function Jordan Niethe
2020-05-04  9:24   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 15/28] powerpc/kprobes: Use patch_instruction() Jordan Niethe
2020-05-05  1:41   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 16/28] powerpc: Define and use __get_user_instr{, inatomic}() Jordan Niethe
2020-05-05  1:46   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 17/28] powerpc: Introduce a function for reporting instruction length Jordan Niethe
2020-05-05  2:02   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 18/28] powerpc/xmon: Use a function for reading instructions Jordan Niethe
2020-05-05  2:07   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 19/28] powerpc/xmon: Move insertion of breakpoint for xol'ing Jordan Niethe
2020-05-05  2:19   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 20/28] powerpc: Make test_translate_branch() independent of instruction length Jordan Niethe
2020-05-05  2:40   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 21/28] powerpc: Enable Prefixed Instructions Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 22/28] powerpc: Define new SRR1 bits for a future ISA version Jordan Niethe
2020-05-05  2:49   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 23/28] powerpc: Add prefixed instructions to instruction data type Jordan Niethe
2020-05-05  6:04   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 24/28] powerpc: Test prefixed code patching Jordan Niethe
2020-05-05  6:08   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 25/28] powerpc: Test prefixed instructions in feature fixups Jordan Niethe
2020-05-05  7:15   ` Alistair Popple
2020-05-05  7:34     ` Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 26/28] powerpc: Support prefixed instructions in alignment handler Jordan Niethe
2020-05-05  7:17   ` Alistair Popple
2020-05-01  3:42 ` [PATCH v7 27/28] powerpc sstep: Add support for prefixed load/stores Jordan Niethe
2020-05-01  3:42 ` [PATCH v7 28/28] powerpc sstep: Add support for prefixed fixed-point arithmetic Jordan Niethe

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