Re: [PATCH 2/4] *-linux-nat: Handle null inferior in read_description.

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

Hi John,

Do you have an example of when this would happen? So, having no inferior and invoking ptrace?

I know this can happen for extended remote mode, but it isn't clear for native gdb.

On 5/26/23 18:57, John Baldwin wrote:
> Don't invoke ptrace in the target read_description method if there is
> not an active inferior to query via ptrace.  Instead, use the default
> register set for the architecture.
> 
> Previously the native target could report an error from a failed
> ptrace operation when fetching a tdesc without an attached process.
> For example on Linux x86-64:
> 
> (gdb) target native
> Done.  Use the "run" command to start a process.
> (gdb) unset tdesc filename
> Couldn't get CS register: No such process.
> ---
>  gdb/aarch64-linux-nat.c | 3 +++
>  gdb/arm-linux-nat.c     | 3 +++
>  gdb/mips-linux-nat.c    | 3 +++
>  gdb/ppc-linux-nat.c     | 3 +++
>  gdb/riscv-linux-nat.c   | 3 +++
>  gdb/s390-linux-nat.c    | 3 +++
>  gdb/x86-linux-nat.c     | 3 +++
>  7 files changed, 21 insertions(+)
> 
> diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
> index ecb2eeb9540..62f8825b9c8 100644
> --- a/gdb/aarch64-linux-nat.c
> +++ b/gdb/aarch64-linux-nat.c
> @@ -785,6 +785,9 @@ aarch64_linux_nat_target::read_description ()
>    gdb_byte regbuf[ARM_VFP3_REGS_SIZE];
>    struct iovec iovec;
>  
> +  if (inferior_ptid == null_ptid)
> +    return nullptr;
> +
>    tid = inferior_ptid.pid ();
>  
>    iovec.iov_base = regbuf;
> diff --git a/gdb/arm-linux-nat.c b/gdb/arm-linux-nat.c
> index ef3fa008adf..70c6bc684fa 100644
> --- a/gdb/arm-linux-nat.c
> +++ b/gdb/arm-linux-nat.c
> @@ -531,6 +531,9 @@ ps_get_thread_area (struct ps_prochandle *ph,
>  const struct target_desc *
>  arm_linux_nat_target::read_description ()
>  {
> +  if (inferior_ptid == null_ptid)
> +    return this->beneath ()->read_description ();
> +
>    CORE_ADDR arm_hwcap = linux_get_hwcap ();
>  
>    if (have_ptrace_getregset == TRIBOOL_UNKNOWN)
> diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c
> index 972b5db8e76..1fa0e8c479c 100644
> --- a/gdb/mips-linux-nat.c
> +++ b/gdb/mips-linux-nat.c
> @@ -454,6 +454,9 @@ mips_linux_nat_target::register_u_offset (struct gdbarch *gdbarch,
>  const struct target_desc *
>  mips_linux_nat_target::read_description ()
>  {
> +  if (inferior_ptid == null_ptid)
> +    return _MIPS_SIM == _ABIO32 ? tdesc_mips_linux : tdesc_mips64_linux;
> +
>    static int have_dsp = -1;
>  
>    if (have_dsp < 0)
> diff --git a/gdb/ppc-linux-nat.c b/gdb/ppc-linux-nat.c
> index 42885deb45e..2f4799aa73a 100644
> --- a/gdb/ppc-linux-nat.c
> +++ b/gdb/ppc-linux-nat.c
> @@ -1941,6 +1941,9 @@ ppc_linux_nat_target::auxv_parse (const gdb_byte **readptr,
>  const struct target_desc *
>  ppc_linux_nat_target::read_description ()
>  {
> +  if (inferior_ptid == null_ptid)
> +    return ppc_linux_match_description (ppc_linux_no_features);
> +
>    int tid = inferior_ptid.pid ();
>  
>    if (have_ptrace_getsetevrregs)
> diff --git a/gdb/riscv-linux-nat.c b/gdb/riscv-linux-nat.c
> index 8be4a5ac3e5..5d325e633da 100644
> --- a/gdb/riscv-linux-nat.c
> +++ b/gdb/riscv-linux-nat.c
> @@ -201,6 +201,9 @@ fill_fpregset (const struct regcache *regcache, prfpregset_t *fpregs,
>  const struct target_desc *
>  riscv_linux_nat_target::read_description ()
>  {
> +  if (inferior_ptid == null_ptid)
> +    return nullptr;
> +
>    const struct riscv_gdbarch_features features
>      = riscv_linux_read_features (inferior_ptid.pid ());
>    return riscv_lookup_target_description (features);
> diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
> index fc3917d30be..7d3b3cfe78b 100644
> --- a/gdb/s390-linux-nat.c
> +++ b/gdb/s390-linux-nat.c
> @@ -987,6 +987,9 @@ s390_linux_nat_target::auxv_parse (const gdb_byte **readptr,
>  const struct target_desc *
>  s390_linux_nat_target::read_description ()
>  {
> +  if (inferior_ptid == null_ptid)
> +    return nullptr;
> +
>    int tid = inferior_ptid.pid ();
>  
>    have_regset_last_break
> diff --git a/gdb/x86-linux-nat.c b/gdb/x86-linux-nat.c
> index fd2145244cc..87862b89eab 100644
> --- a/gdb/x86-linux-nat.c
> +++ b/gdb/x86-linux-nat.c
> @@ -115,6 +115,9 @@ x86_linux_nat_target::read_description ()
>    static uint64_t xcr0;
>    uint64_t xcr0_features_bits;
>  
> +  if (inferior_ptid == null_ptid)
> +    return nullptr;
> +
>    tid = inferior_ptid.pid ();
>  
>  #ifdef __x86_64__