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SubjectRe: [PATCH v5 4/7] arm64: introduce aarch64_insn_gen_{nop|branch_imm}() helper functions
On Fri, Oct 18, 2013 at 04:19:58PM +0100, Jiang Liu wrote:
> From: Jiang Liu <jiang.liu@huawei.com>
>
> Introduce aarch64_insn_gen_{nop|branch_imm}() helper functions, which
> will be used to implement jump label on ARM64.
>
> Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
> Cc: Jiang Liu <liuj97@gmail.com>
> ---
> arch/arm64/include/asm/insn.h | 13 +++++++++++++
> arch/arm64/kernel/insn.c | 28 ++++++++++++++++++++++++++++
> 2 files changed, 41 insertions(+)
>
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index 8f94e48..ee4a60d 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -96,9 +96,22 @@ static __always_inline void aarch64_insn_write(void *addr, u32 insn)
> *(u32 *)addr = cpu_to_le32(insn);
> }
>
> +static __always_inline u32 aarch64_insn_gen_hint(enum aarch64_insn_hint_op op)
> +{
> + return aarch64_insn_get_hint_value() | op;

What's the point in that helper function? Does it just return an immediate
value (and are there are other users of it?).

> +}
> +
> +static __always_inline u32 aarch64_insn_gen_nop(void)
> +{
> + return aarch64_insn_gen_hint(AARCH64_INSN_HINT_NOP);
> +}

Either use plain old `inline' or write these as preprocessor macros.

> +
> enum aarch64_insn_encoding_class aarch64_get_insn_class(u32 insn);
> u32 aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
> u32 insn, u64 imm);
> +u32 aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
> + bool link);
> +
> bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);
>
> int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
> index 886821f..f7498cc 100644
> --- a/arch/arm64/kernel/insn.c
> +++ b/arch/arm64/kernel/insn.c
> @@ -14,6 +14,7 @@
> * You should have received a copy of the GNU General Public License
> * along with this program. If not, see <http://www.gnu.org/licenses/>.
> */
> +#include <linux/bitops.h>
> #include <linux/compiler.h>
> #include <linux/kernel.h>
> #include <linux/smp.h>
> @@ -233,3 +234,30 @@ u32 aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
>
> return insn;
> }
> +
> +u32 aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr, bool link)
> +{
> + u32 insn;
> + long offset;
> +
> + /*
> + * PC: A 64-bit Program Counter holding the address of the current
> + * instruction. A64 instructions may be word-aligned.
> + */
> + BUG_ON((pc & 0x3) || (addr & 0x3));
> +
> + /*
> + * B/BL support [-128M, 128M) offset
> + * ARM64 virtual address arrangement garantees all kernel and module

Typo: `guarantees'.

> + * texts are within +/-128M.
> + */
> + offset = ((long)addr - (long)pc) >> 2;
> + BUG_ON(abs(offset) > BIT(25) || offset == BIT(25));

I really struggle to follow this range checking. Why don't you just compare
the absolute difference between addr and pc with SZ_128M?

Will


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