[PATCH v3 1/2] arm64: module-plts: factor out PLT generation code for ftrace

[will.deacon@arm.com (Will Deacon)]

On Mon, Nov 20, 2017 at 05:41:29PM +0000, Ard Biesheuvel wrote:
> To allow the ftrace trampoline code to reuse the PLT entry routines,
> factor it out and move it into asm/module.h.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> v3: new patch
> 
>  arch/arm64/include/asm/module.h | 44 ++++++++++++++++++++
>  arch/arm64/kernel/module-plts.c | 38 +----------------
>  2 files changed, 46 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h
> index 19bd97671bb8..11d4aaee82e1 100644
> --- a/arch/arm64/include/asm/module.h
> +++ b/arch/arm64/include/asm/module.h
> @@ -45,4 +45,48 @@ extern u64 module_alloc_base;
>  #define module_alloc_base	((u64)_etext - MODULES_VSIZE)
>  #endif
>  
> +struct plt_entry {
> +	/*
> +	 * A program that conforms to the AArch64 Procedure Call Standard
> +	 * (AAPCS64) must assume that a veneer that alters IP0 (x16) and/or
> +	 * IP1 (x17) may be inserted at any branch instruction that is
> +	 * exposed to a relocation that supports long branches. Since that
> +	 * is exactly what we are dealing with here, we are free to use x16
> +	 * as a scratch register in the PLT veneers.
> +	 */
> +	__le32	mov0;	/* movn	x16, #0x....			*/
> +	__le32	mov1;	/* movk	x16, #0x...., lsl #16		*/
> +	__le32	mov2;	/* movk	x16, #0x...., lsl #32		*/
> +	__le32	br;	/* br	x16				*/
> +};
> +
> +static inline struct plt_entry get_plt_entry(u64 val)
> +{
> +	/*
> +	 * MOVK/MOVN/MOVZ opcode:
> +	 * +--------+------------+--------+-----------+-------------+---------+
> +	 * | sf[31] | opc[30:29] | 100101 | hw[22:21] | imm16[20:5] | Rd[4:0] |
> +	 * +--------+------------+--------+-----------+-------------+---------+
> +	 *
> +	 * Rd     := 0x10 (x16)
> +	 * hw     := 0b00 (no shift), 0b01 (lsl #16), 0b10 (lsl #32)
> +	 * opc    := 0b11 (MOVK), 0b00 (MOVN), 0b10 (MOVZ)
> +	 * sf     := 1 (64-bit variant)
> +	 */
> +	return (struct plt_entry){
> +		cpu_to_le32(0x92800010 | (((~val      ) & 0xffff)) << 5),
> +		cpu_to_le32(0xf2a00010 | ((( val >> 16) & 0xffff)) << 5),
> +		cpu_to_le32(0xf2c00010 | ((( val >> 32) & 0xffff)) << 5),
> +		cpu_to_le32(0xd61f0200)
> +	};
> +}

Not one for this series, but do you think we could use insn.c to generate
these?

Will