Re: [Qemu-devel] [PATCH v2 3/4] linux-user, m68k: select CPU according to ELF header values

[Richard Henderson <richard.henderson@linaro.org>]

On 01/16/2018 09:25 AM, Laurent Vivier wrote:
> M680x0 doesn't support the same set of instructions
> as ColdFire, so we can't use "any" CPU type to execute
> m68020 instructions.
> We select CPU type ("m68020" or "any" for ColdFire)
> according to the ELF header. If we can't, we
> use by default the value used until now: "any".
> 
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
> 
> Notes:
>     v2: call cpu_get_model() with the result of get_elf_eflags()
> 
>  linux-user/m68k/target_elf.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/linux-user/m68k/target_elf.h b/linux-user/m68k/target_elf.h
> index df375ad5d3..946b90f342 100644
> --- a/linux-user/m68k/target_elf.h
> +++ b/linux-user/m68k/target_elf.h
> @@ -9,6 +9,12 @@
>  #define M68K_TARGET_ELF_H
>  static inline const char *cpu_get_model(uint32_t eflags)
>  {
> +    if (eflags == 0) {
> +        /* 680x0 */
> +        return "m68020";
> +    }
> +
> +    /* Coldfire */
>      return "any";

This isn't quite right.  From binutils:

/* We use the top 24 bits to encode information about the
   architecture variant.  */
#define EF_M68K_CPU32    0x00810000
#define EF_M68K_M68000   0x01000000
#define EF_M68K_CFV4E    0x00008000
#define EF_M68K_FIDO     0x02000000
#define EF_M68K_ARCH_MASK                                               \
  (EF_M68K_M68000 | EF_M68K_CPU32 | EF_M68K_CFV4E | EF_M68K_FIDO)

/* We use the bottom 8 bits to encode information about the
   coldfire variant.  If we use any of these bits, the top 24 bits are
   either 0 or EF_M68K_CFV4E.  */
#define EF_M68K_CF_ISA_MASK     0x0F  /* Which ISA */
#define EF_M68K_CF_ISA_A_NODIV  0x01  /* ISA A except for div */
#define EF_M68K_CF_ISA_A        0x02
#define EF_M68K_CF_ISA_A_PLUS   0x03
#define EF_M68K_CF_ISA_B_NOUSP  0x04  /* ISA_B except for USP */
#define EF_M68K_CF_ISA_B        0x05
#define EF_M68K_CF_ISA_C        0x06
#define EF_M68K_CF_ISA_C_NODIV  0x07  /* ISA C except for div */
#define EF_M68K_CF_MAC_MASK     0x30
#define EF_M68K_CF_MAC          0x10  /* MAC */
#define EF_M68K_CF_EMAC         0x20  /* EMAC */
#define EF_M68K_CF_EMAC_B       0x30  /* EMAC_B */
#define EF_M68K_CF_FLOAT        0x40  /* Has float insns */
#define EF_M68K_CF_MASK         0xFF

It looks like m68000 series for flags == 0 || flags & EF_M68K_M68000.

While we're at it, surely 68040 is a better default than 68020 for user-only,
especially once all your fpu patches are in.


r~