Re: [PATCH] [aarch64] tpidr2: Fix erroneous detection logic for TPIDR2

[Luis Machado <luis.machado@arm.com>]

On 3/14/23 14:22, Luis Machado via Gdb-patches wrote:
> The detection logic for TPIDR2 was implemented incorrectly.  Originally
> the detection was supposed to be through a ptrace error code, but in reality,
> for backwards compatibility, the detection should be based on the size of
> the returned iovec.
> 
> For instance, if a target supports both TPIDR and TPIDR2, ptrace will return a
> iovec size of 16.  If a target only supports TPIDR and not TPIDR2, it will
> return a iovec size of 8, even if we asked for 16 bytes.
> 
> This patch fixes this issue in code that is shared between gdb and gdbserver,
> therefore both gdb and gdbserver are fixed.
> 
> Tested on AArch64/Linux Ubuntu 20.04.
> ---
>   gdb/nat/aarch64-linux.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/gdb/nat/aarch64-linux.c b/gdb/nat/aarch64-linux.c
> index 6c8a78f1729..a84faf1cfbf 100644
> --- a/gdb/nat/aarch64-linux.c
> +++ b/gdb/nat/aarch64-linux.c
> @@ -261,13 +261,13 @@ aarch64_tls_register_count (int tid)
>     iovec.iov_base = tls_regs;
>     iovec.iov_len = sizeof (tls_regs);
>   
> -  /* Attempt to read both TPIDR and TPIDR2.  If the request fails, it means
> -     the Linux Kernel does not support TPIDR2.
> -
> -     Otherwise the Linux Kernel supports both TPIDR and TPIDR2.  */
> +  /* Attempt to read both TPIDR and TPIDR2.  If ptrace returns less data than
> +     we are expecting, that means it doesn't support all the registers.  From
> +     the iovec length, figure out how many TPIDR registers the target actually
> +     supports.  */
>     if (ptrace (PTRACE_GETREGSET, tid, NT_ARM_TLS, &iovec) != 0)
> -    return 1;
> +    return 0;
>   
> -  /* TPIDR2 is available as well.  */
> -  return 2;
> +  /* Calculate how many TPIDR registers we have.  */
> +  return iovec.iov_len / sizeof (uint64_t);
>   }

Pushed now as d747348d02f12121a2e897f7789ff27ffbd2f23d.