Re: [PATCH v2 2/6] [gdbserver/aarch64] sme2: Enable SME2 support in gdbserver

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Luis Machado <luis.machado@arm.com> writes:

> This patch teaches gdbserver about the SME2 and the ZT0 register.
>
> Since most of the code used by gdbserver for SME2 is shared with gdb, this
> is a rather small patch that reuses most of the code put in place for native
> AArch64 Linux.
>
> Validated under Fast Models.
> ---
>  gdbserver/linux-aarch64-low.cc | 63 ++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index 95688480c3d..783053e359b 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -811,6 +811,52 @@ aarch64_za_regs_copy_from_regcache (struct regcache *regcache, void *buf)
>    memcpy (buf, za_state.data (), za_state.size ());
>  }
>  
> +/* Wrapper for aarch64_zt_regs_copy_to_reg_buf, to help copying NT_ARM_ZT
> +   state from the thread (BUF) to the register cache.  */
> +
> +static void
> +aarch64_zt_regs_copy_to_regcache (struct regcache *regcache,
> +				  ATTRIBUTE_UNUSED const void *buf)
> +{
> +  /* BUF is unused here since we collect the data straight from a ptrace
> +     request, therefore bypassing gdbserver's own call to ptrace.  */
> +  int tid = lwpid_of (current_thread);
> +
> +  gdb::optional<int> zt_regnum
> +    = find_regno_no_throw (regcache->tdesc, "zt0");
> +
> +  gdb_assert (zt_regnum.has_value ());

If this code is changed to use find_regno(), this gdb_assert() becomes
unnecessary.

> +
> +  /* Update the register cache.  aarch64_zt_regs_copy_to_reg_buf handles
> +     fetching the NT_ARM_ZT state from thread TID.  */
> +  aarch64_zt_regs_copy_to_reg_buf (tid, regcache, *zt_regnum);
> +}
> +
> +/* Wrapper for aarch64_zt_regs_copy_from_reg_buf, to help copying NT_ARM_ZT
> +   state from the register cache to the thread (BUF).  */
> +
> +static void
> +aarch64_zt_regs_copy_from_regcache (struct regcache *regcache, void *buf)
> +{
> +  int tid = lwpid_of (current_thread);
> +
> +  gdb::optional<int> zt_regnum
> +    = find_regno_no_throw (regcache->tdesc, "za");
> +
> +  gdb_assert (zt_regnum.has_value ());

Same comment about find_regno().

> +
> +  /* Update the thread NT_ARM_ZT state.  aarch64_zt_regs_copy_from_reg_buf
> +     handles writing the ZT state back to thread TID.  */
> +  aarch64_zt_regs_copy_from_reg_buf (tid, regcache, *zt_regnum);
> +
> +  /* We need to return the expected data in BUF, so copy whatever the kernel
> +     already has to BUF.  */
> +
> +  /* Obtain a dump of NT_ARM_ZT from ptrace.  */
> +  gdb::byte_vector zt_state = aarch64_fetch_zt_regset (tid);
> +  memcpy (buf, zt_state.data (), zt_state.size ());
> +}
> +
>  /* Array containing all the possible register sets for AArch64/Linux.  During
>     architecture setup, these will be checked against the HWCAP/HWCAP2 bits for
>     validity and enabled/disabled accordingly.
> @@ -838,6 +884,11 @@ static struct regset_info aarch64_regsets[] =
>      0, EXTENDED_REGS,
>      aarch64_za_regs_copy_from_regcache, aarch64_za_regs_copy_to_regcache
>    },
> +  /* Scalable Matrix Extension 2 (SME2) ZT registers.  */
> +  { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_ARM_ZT,
> +    0, EXTENDED_REGS,
> +    aarch64_zt_regs_copy_from_regcache, aarch64_zt_regs_copy_to_regcache
> +  },
>    /* PAC registers.  */
>    { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_ARM_PAC_MASK,
>      0, OPTIONAL_REGS,
> @@ -909,6 +960,10 @@ aarch64_adjust_register_sets (const struct aarch64_features &features)
>  	  if (features.svq > 0)
>  	    regset->size = ZA_PT_SIZE (features.svq);
>  	  break;
> +	case NT_ARM_ZT:
> +	  if (features.sme2)
> +	    regset->size = 64;

Suggest using AARCH64_SME2_ZT0_SIZE here.

> +	  break;
>  	default:
>  	  gdb_assert_not_reached ("Unknown register set found.");
>  	}
> @@ -947,6 +1002,14 @@ aarch64_target::low_arch_setup ()
>        if (linux_get_hwcap2 (pid, 8) & HWCAP2_SME)
>  	features.svq = aarch64_za_get_svq (tid);
>  
> +      /* Scalable Matrix Extension 2 feature check.  */
> +      CORE_ADDR hwcap2 = linux_get_hwcap2 (pid, 8);
> +      if ((hwcap2 & HWCAP2_SME2) || (hwcap2 & HWCAP2_SME2P1))
> +	{
> +	  /* Make sure ptrace supports NT_ARM_ZT.  */
> +	  features.sme2 = supports_zt_registers (tid);
> +	}
> +
>        current_process ()->tdesc = aarch64_linux_read_description (features);
>  
>        /* Adjust the register sets we should use for this particular set of

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

-- 
Thiago