Re: [Qemu-ppc] [PATCH v4 2/3] target/ppc: Add GDB callbacks for SPRs

[Alexey Kardashevskiy]

On 23/01/2019 04:01, Fabiano Rosas wrote:
> These will be used to let GDB know about PPC's Special Purpose
> Registers (SPR).
> 
> They take an index based on the order the registers appear in the XML
> file sent by QEMU to GDB. This index does not match the actual
> location of the registers in the env->spr array so the
> gdb_find_spr_idx function does that conversion.
> 
> Signed-off-by: Fabiano Rosas <address@hidden>
> ---
>  target/ppc/translate_init.inc.c | 54 ++++++++++++++++++++++++++++++++-
>  1 file changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
> index 710064a25d..f29ac3558a 100644
> --- a/target/ppc/translate_init.inc.c
> +++ b/target/ppc/translate_init.inc.c
> @@ -9487,6 +9487,55 @@ static bool avr_need_swap(CPUPPCState *env)
>  #endif
>  }
>  
> +#if !defined(CONFIG_USER_ONLY)
> +static int gdb_find_spr_idx(CPUPPCState *env, int n)
> +{
> +    int i;
> +
> +    for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
> +        ppc_spr_t *spr = &env->spr_cb[i];
> +
> +        if (spr->name && spr->gdb_id == n) {
> +            return i;
> +        }
> +    }
> +    return -1;
> +}
> +
> +static int gdb_get_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
> +{
> +    int reg;
> +    int len;
> +
> +    reg = gdb_find_spr_idx(env, n);
> +    if (reg < 0) {
> +        return 0;
> +    }
> +
> +    len = TARGET_LONG_SIZE;
> +    stn_p(mem_buf, len, env->spr[reg]);
> +    ppc_maybe_bswap_register(env, mem_buf, len);


I am confused by this as it produces different results depending on the
guest mode:

(gdb) p $pvr
$1 = 0x14c0000000000
(gdb) c
Continuing.
Program received signal SIGINT, Interrupt.
(gdb) p $pvr
$2 = 0x4c0100


First print is when I stopped the guest in the SLOF firmware (so it is
big-endian) and then I continued and stopped gdb when the guest booted a
little-endian system; the KVM host is little endian, the machine running
gdb is LE too.

QEMU monitor prints the same 0x4c0100 in both cases.

I am adding the inventor of maybe_bswap_register() in cc: for
assistance. Swapping happens:
- once for BE: after stn_p()
        *(unsigned long *)mem_buf is 0x14c0000000000
- twice for LE.





> +    return len;
> +}
> +
> +static int gdb_set_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
> +{
> +    int reg;
> +    int len;
> +
> +    reg = gdb_find_spr_idx(env, n);
> +    if (reg < 0) {
> +        return 0;
> +    }
> +
> +    len = TARGET_LONG_SIZE;
> +    ppc_maybe_bswap_register(env, mem_buf, len);
> +    env->spr[reg] = ldn_p(mem_buf, len);
> +
> +    return len;
> +}
> +#endif
> +
>  static int gdb_get_float_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
>  {
>      if (n < 32) {
> @@ -9716,7 +9765,10 @@ static void ppc_cpu_realize(DeviceState *dev, Error 
> **errp)
>          gdb_register_coprocessor(cs, gdb_get_vsx_reg, gdb_set_vsx_reg,
>                                   32, "power-vsx.xml", 0);
>      }
> -
> +#ifndef CONFIG_USER_ONLY
> +    gdb_register_coprocessor(cs, gdb_get_spr_reg, gdb_set_spr_reg,
> +                             pcc->gdb_num_sprs, "power-spr.xml", 0);
> +#endif
>      qemu_init_vcpu(cs);
>  
>      pcc->parent_realize(dev, errp);
> 

-- 
Alexey