On Wed, 14 Dec 2016 21:48:30 +0530
Anju T Sudhakar <a...@linux.vnet.ibm.com> wrote:
> From: "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com>
>
The coding is OK to me. Please add a description for this patch
here, e.g. what is done by this patch, what kind of branch
instruction will be covered, and why thse checks are needed etc.
Thank you,
> Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> Signed-off-by: Anju T Sudhakar <a...@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/code-patching.h | 1 +
> arch/powerpc/lib/code-patching.c | 24 +++++++++++++++++++++++-
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/code-patching.h
> b/arch/powerpc/include/asm/code-patching.h
> index 2015b07..75ee4f4 100644
> --- a/arch/powerpc/include/asm/code-patching.h
> +++ b/arch/powerpc/include/asm/code-patching.h
> @@ -22,6 +22,7 @@
> #define BRANCH_SET_LINK 0x1
> #define BRANCH_ABSOLUTE 0x2
>
> +bool is_offset_in_branch_range(long offset);
> unsigned int create_branch(const unsigned int *addr,
> unsigned long target, int flags);
> unsigned int create_cond_branch(const unsigned int *addr,
> diff --git a/arch/powerpc/lib/code-patching.c
> b/arch/powerpc/lib/code-patching.c
> index d5edbeb..f643451 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -32,6 +32,28 @@ int patch_branch(unsigned int *addr, unsigned long target,
> int flags)
> return patch_instruction(addr, create_branch(addr, target, flags));
> }
>
> +bool is_offset_in_branch_range(long offset)
> +{
> + /*
> + * Powerpc branch instruction is :
> + *
> + * 0 6 30 31
> + * +---------+----------------+---+---+
> + * | opcode | LI |AA |LK |
> + * +---------+----------------+---+---+
> + * Where AA = 0 and LK = 0
> + *
> + * LI is a signed 24 bits integer. The real branch offset is computed
> + * by: imm32 = SignExtend(LI:'0b00', 32);
> + *
> + * So the maximum forward branch should be:
> + * (0x007fffff << 2) = 0x01fffffc = 0x1fffffc
> + * The maximum backward branch should be:
> + * (0xff800000 << 2) = 0xfe000000 = -0x2000000
> + */
> + return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
> +}
> +
> unsigned int create_branch(const unsigned int *addr,
> unsigned long target, int flags)
> {
> @@ -43,7 +65,7 @@ unsigned int create_branch(const unsigned int *addr,
> offset = offset - (unsigned long)addr;
>
> /* Check we can represent the target in the instruction format */
> - if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3)
> + if (!is_offset_in_branch_range(offset))
> return 0;
>
> /* Mask out the flags and target, so they don't step on each other. */
> --
> 2.7.4
>
--
Masami Hiramatsu <mhira...@kernel.org>
