Re: [PATCH v3 4/6] linux-user/elfload: Introduce MIPS GET_FEATURE_REG_EQU() macro

[Richard Henderson]

On 12/1/20 1:28 PM, Philippe Mathieu-Daudé wrote:
> ISA features are usually denoted in read-only bits from
> CPU registers. Add the GET_FEATURE_REG_EQU() macro which
> checks if a CPU register has bits set to a specific value.
> 
> Use the macro to check the 'Architecture Revision' level
> of the Config0 register, which is '2' when the Release 6
> ISA is implemented.
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/elfload.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index b7c6d30723a..9c475fa5f70 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -7,6 +7,7 @@
>  
>  #include "qemu.h"
>  #include "disas/disas.h"
> +#include "qemu/bitops.h"
>  #include "qemu/path.h"
>  #include "qemu/queue.h"
>  #include "qemu/guest-random.h"
> @@ -995,17 +996,25 @@ enum {
>  #define GET_FEATURE_REG_SET(_reg, _mask, _hwcap) \
>      do { if (cpu->env._reg & (_mask)) { hwcaps |= _hwcap; } } while (0)
>  
> +#define GET_FEATURE_REG_EQU(_reg, _start, _length, _val, _hwcap) \
> +    do { \
> +        if (extract32(cpu->env._reg, (_start), (_length)) == (_val)) { \
> +            hwcaps |= _hwcap; \
> +        } \
> +    } while (0)
> +
>  static uint32_t get_elf_hwcap(void)
>  {
>      MIPSCPU *cpu = MIPS_CPU(thread_cpu);
>      uint32_t hwcaps = 0;
>  
> -    GET_FEATURE_INSN(ISA_MIPS32R6 | ISA_MIPS64R6, HWCAP_MIPS_R6);
> +    GET_FEATURE_REG_EQU(CP0_Config0, CP0C0_AR, 3, 2, HWCAP_MIPS_R6);

You still get the magic 3.

This is where hw/registerfields.h would come in handy.  But that is certainly a
large change to mips' cpu.h.  So I guess this is good enough for now.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~