Messages in this thread | | | Date | Fri, 16 Dec 2016 20:52:21 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH V2 2/4] powerpc: add helper to check if offset is within rel branch range |
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On Wed, 14 Dec 2016 21:48:30 +0530 Anju T Sudhakar <anju@linux.vnet.ibm.com> wrote:
> From: "Naveen N. Rao" <naveen.n.rao@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.rao@linux.vnet.ibm.com> > Signed-off-by: Anju T Sudhakar <anju@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 <mhiramat@kernel.org>
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