[PATCH 1/4] Add generic ARM instruction set condition code checks.

[Dave Martin]

On Fri, Nov 25, 2011 at 05:19:23PM +0000, Leif Lindholm wrote:
> This patch breaks the ARM condition checking code out of nwfpe/fpopcode.{ch}
> into a standalone file for opcode operations. It also modifies the code
> somewhat for coding style adherence, and adds some temporary variables for
> increased readability.
> 
> Signed-off-by: Leif Lindholm <leif.lindholm at arm.com>
> ---
>  arch/arm/include/asm/opcodes.h |   20 ++++++++++++
>  arch/arm/kernel/Makefile       |    2 +
>  arch/arm/kernel/opcodes.c      |   68 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 89 insertions(+), 1 deletions(-)
>  create mode 100644 arch/arm/include/asm/opcodes.h
>  create mode 100644 arch/arm/kernel/opcodes.c
> 
> diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
> new file mode 100644
> index 0000000..aea97bf
> --- /dev/null
> +++ b/arch/arm/include/asm/opcodes.h
> @@ -0,0 +1,20 @@
> +/*
> + *  arch/arm/include/asm/opcodes.h
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#ifndef __ASM_ARM_OPCODES_H
> +#define __ASM_ARM_OPCODES_H
> +
> +#ifndef __ASSEMBLY__
> +extern unsigned int arm_check_condition(unsigned int opcode, unsigned int psr);
> +#endif
> +
> +#define ARM_OPCODE_CONDTEST_FAIL   0
> +#define ARM_OPCODE_CONDTEST_PASS   1
> +#define ARM_OPCODE_CONDTEST_UNCOND 2
> +
> +#endif /* __ASM_ARM_OPCODES_H */
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 16eed6a..43b740d 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -13,7 +13,7 @@ CFLAGS_REMOVE_return_address.o = -pg
>  
>  # Object file lists.
>  
> -obj-y		:= elf.o entry-armv.o entry-common.o irq.o \
> +obj-y		:= elf.o entry-armv.o entry-common.o irq.o opcodes.o \
>  		   process.o ptrace.o return_address.o setup.o signal.o \
>  		   sys_arm.o stacktrace.o time.o traps.o
>  
> diff --git a/arch/arm/kernel/opcodes.c b/arch/arm/kernel/opcodes.c
> new file mode 100644
> index 0000000..c3171cc
> --- /dev/null
> +++ b/arch/arm/kernel/opcodes.c
> @@ -0,0 +1,68 @@
> +/*
> + *  linux/arch/arm/kernel/opcodes.c
> + *
> + *  A32 condition code lookup feature moved from nwfpe/fpopcode.c
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/module.h>
> +#include <asm/opcodes.h>
> +
> +#define ARM_OPCODE_CONDITION_UNCOND 0xf
> +
> +/*
> + * condition code lookup table
> + * index into the table is test code: EQ, NE, ... LT, GT, AL, NV
> + *
> + * bit position in short is condition code: NZCV
> + */
> +static const unsigned short cc_map[16] = {
> +	0xF0F0,			/* EQ == Z set            */
> +	0x0F0F,			/* NE                     */
> +	0xCCCC,			/* CS == C set            */
> +	0x3333,			/* CC                     */
> +	0xFF00,			/* MI == N set            */
> +	0x00FF,			/* PL                     */
> +	0xAAAA,			/* VS == V set            */
> +	0x5555,			/* VC                     */
> +	0x0C0C,			/* HI == C set && Z clear */
> +	0xF3F3,			/* LS == C clear || Z set */
> +	0xAA55,			/* GE == (N==V)           */
> +	0x55AA,			/* LT == (N!=V)           */
> +	0x0A05,			/* GT == (!Z && (N==V))   */
> +	0xF5FA,			/* LE == (Z || (N!=V))    */
> +	0xFFFF,			/* AL always              */
> +	0			/* NV                     */
> +};
> +
> +/*
> + * Returns:
> + * ARM_OPCODE_CONDTEST_FAIL   - if condition fails
> + * ARM_OPCODE_CONDTEST_PASS   - if condition passes (including AL)
> + * ARM_OPCODE_CONDTEST_UNCOND - if NV condition, or separate unconditional
> + *                              opcode space from v5 onwards
> + *
> + * Code that needs to check whether a condition has explicitly passed,
> + * should compare the return value to 1.

This paragraph should refer to the symbolic constants -- there's not so
much point having them if people hard-code integer comparisons into all
the calling code.

The wording feels a bit confusing too.  Maybe something like:

"Code that needs to check when an instruction is conditional and would
pass its condition check should check whether the return value ==
ARM_OPCODE_CONDTEST_PASS."


> + * Code that wants to check if a condition means that the instruction
> + * should be executed, should compare the return value to !0.

!0 == 1.  I guess this is not what you mean.

Maybe:

"Code that needs to check when an instruction would architecturally
execute (including some instructions on ARMv5 and later which cannot be
conditional) should check whether the return value !=
ARM_OPCODE_CONDTEST_FAIL."

This documentation should perhaps move to opcodes.h, but I don't have a
strong opinion.

> + */
> +unsigned int arm_check_condition(unsigned int opcode, unsigned int psr)
> +{
> +	unsigned int cc_bits  = opcode >> 28;
> +	unsigned int psr_cond = psr >> 28;
> +
> +	if (cc_bits != ARM_OPCODE_CONDITION_UNCOND) {
> +		if ((cc_map[cc_bits] >> (psr_cond)) & 1)
> +			return ARM_OPCODE_CONDTEST_PASS;
> +		else
> +			return ARM_OPCODE_CONDTEST_FAIL;
> +	 } else {

Remove the space before } (checkpatch.pl ought to pick this up)

> +		return ARM_OPCODE_CONDTEST_UNCOND;
> +	}
> +}
> +
> +EXPORT_SYMBOL(arm_check_condition);

Cheers
---Dave