Re: [PATCH v3 2/8] gdbserver: Add PID parameter to linux_get_auxv and linux_get_hwcap

[Andrew Burgess <aburgess@redhat.com>]

Thiago Jung Bauermann via Gdb-patches <gdb-patches@sourceware.org>
writes:

> This patch doesn't change gdbserver behaviour, but after later changes are
> made it avoids a null pointer dereference when HWCAP needs to be obtained
> for a specific process while current_thread is nullptr.
>
> Fixing linux_read_auxv, linux_get_hwcap and linux_get_hwcap2 to take a PID
> parameter seems more correct than setting current_thread in one particular
> code path.
>
> Changes are propagated to allow passing the new parameter through the call
> chain.
>
> Approved-By: Simon Marchi <simon.marchi@efficios.com>
> ---
>  gdbserver/linux-aarch64-low.cc |  7 ++++---
>  gdbserver/linux-arm-low.cc     |  2 +-
>  gdbserver/linux-low.cc         | 18 +++++++++---------
>  gdbserver/linux-low.h          |  9 ++++-----
>  gdbserver/linux-ppc-low.cc     |  6 +++---
>  gdbserver/linux-s390-low.cc    |  2 +-
>  gdbserver/netbsd-low.cc        |  4 +---
>  gdbserver/netbsd-low.h         |  2 +-
>  gdbserver/server.cc            |  3 ++-
>  gdbserver/target.cc            |  4 ++--
>  gdbserver/target.h             |  4 ++--
>  11 files changed, 30 insertions(+), 31 deletions(-)
>
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index 3c09e086afee..2ed6e95562c5 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -846,12 +846,13 @@ aarch64_target::low_arch_setup ()
>    if (is_elf64)
>      {
>        struct aarch64_features features;
> +      int pid = current_thread->id.pid ();
>  
>        features.vq = aarch64_sve_get_vq (tid);
>        /* A-profile PAC is 64-bit only.  */
> -      features.pauth = linux_get_hwcap (8) & AARCH64_HWCAP_PACA;
> +      features.pauth = linux_get_hwcap (pid, 8) & AARCH64_HWCAP_PACA;
>        /* A-profile MTE is 64-bit only.  */
> -      features.mte = linux_get_hwcap2 (8) & HWCAP2_MTE;
> +      features.mte = linux_get_hwcap2 (pid, 8) & HWCAP2_MTE;
>        features.tls = aarch64_tls_register_count (tid);
>  
>        current_process ()->tdesc = aarch64_linux_read_description (features);
> @@ -3322,7 +3323,7 @@ aarch64_target::supports_memory_tagging ()
>  #endif
>      }
>  
> -  return (linux_get_hwcap2 (8) & HWCAP2_MTE) != 0;
> +  return (linux_get_hwcap2 (current_thread->id.pid (), 8) & HWCAP2_MTE) != 0;
>  }
>  
>  bool
> diff --git a/gdbserver/linux-arm-low.cc b/gdbserver/linux-arm-low.cc
> index 98ba0e02524b..5975b44af0ae 100644
> --- a/gdbserver/linux-arm-low.cc
> +++ b/gdbserver/linux-arm-low.cc
> @@ -958,7 +958,7 @@ get_next_pcs_syscall_next_pc (struct arm_get_next_pcs *self)
>  static const struct target_desc *
>  arm_read_description (void)
>  {
> -  unsigned long arm_hwcap = linux_get_hwcap (4);
> +  unsigned long arm_hwcap = linux_get_hwcap (current_thread->id.pid (), 4);
>  
>    if (arm_hwcap & HWCAP_IWMMXT)
>      return arm_linux_read_description (ARM_FP_TYPE_IWMMXT);
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index 7e1de3978933..5cd22824e470 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -5483,12 +5483,11 @@ linux_process_target::supports_read_auxv ()
>     to debugger memory starting at MYADDR.  */
>  
>  int
> -linux_process_target::read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> -				 unsigned int len)
> +linux_process_target::read_auxv (int pid, CORE_ADDR offset,
> +				 unsigned char *myaddr, unsigned int len)
>  {
>    char filename[PATH_MAX];
>    int fd, n;
> -  int pid = lwpid_of (current_thread);
>  
>    xsnprintf (filename, sizeof filename, "/proc/%d/auxv", pid);
>  
> @@ -6982,14 +6981,15 @@ linux_get_pc_64bit (struct regcache *regcache)
>  /* See linux-low.h.  */
>  
>  int
> -linux_get_auxv (int wordsize, CORE_ADDR match, CORE_ADDR *valp)
> +linux_get_auxv (int pid, int wordsize, CORE_ADDR match, CORE_ADDR *valp)
>  {
>    gdb_byte *data = (gdb_byte *) alloca (2 * wordsize);
>    int offset = 0;
>  
>    gdb_assert (wordsize == 4 || wordsize == 8);
>  
> -  while (the_target->read_auxv (offset, data, 2 * wordsize) == 2 * wordsize)
> +  while (the_target->read_auxv (pid, offset, data, 2 * wordsize)
> +	 == 2 * wordsize)
>      {
>        if (wordsize == 4)
>  	{
> @@ -7019,20 +7019,20 @@ linux_get_auxv (int wordsize, CORE_ADDR match, CORE_ADDR *valp)
>  /* See linux-low.h.  */
>  
>  CORE_ADDR
> -linux_get_hwcap (int wordsize)
> +linux_get_hwcap (int pid, int wordsize)
>  {
>    CORE_ADDR hwcap = 0;
> -  linux_get_auxv (wordsize, AT_HWCAP, &hwcap);
> +  linux_get_auxv (pid, wordsize, AT_HWCAP, &hwcap);
>    return hwcap;
>  }
>  
>  /* See linux-low.h.  */
>  
>  CORE_ADDR
> -linux_get_hwcap2 (int wordsize)
> +linux_get_hwcap2 (int pid, int wordsize)
>  {
>    CORE_ADDR hwcap2 = 0;
> -  linux_get_auxv (wordsize, AT_HWCAP2, &hwcap2);
> +  linux_get_auxv (pid, wordsize, AT_HWCAP2, &hwcap2);
>    return hwcap2;
>  }
>  
> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
> index aebfe05707e5..221de85aa2ee 100644
> --- a/gdbserver/linux-low.h
> +++ b/gdbserver/linux-low.h
> @@ -178,7 +178,7 @@ class linux_process_target : public process_stratum_target
>  
>    bool supports_read_auxv () override;
>  
> -  int read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> +  int read_auxv (int pid, CORE_ADDR offset, unsigned char *myaddr,
>  		 unsigned int len) override;
>  
>    int insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
> @@ -946,17 +946,16 @@ extern int have_ptrace_getregset;
>     *VALP and return 1.  If not found or if there is an error, return
>     0.  */
>  
> -int linux_get_auxv (int wordsize, CORE_ADDR match,
> -		    CORE_ADDR *valp);
> +int linux_get_auxv (int pid, int wordsize, CORE_ADDR match, CORE_ADDR *valp);
>  
>  /* Fetch the AT_HWCAP entry from the auxv vector, where entries are length
>     WORDSIZE.  If no entry was found, return zero.  */
>  
> -CORE_ADDR linux_get_hwcap (int wordsize);
> +CORE_ADDR linux_get_hwcap (int pid, int wordsize);
>  
>  /* Fetch the AT_HWCAP2 entry from the auxv vector, where entries are length
>     WORDSIZE.  If no entry was found, return zero.  */
>  
> -CORE_ADDR linux_get_hwcap2 (int wordsize);
> +CORE_ADDR linux_get_hwcap2 (int pid, int wordsize);

Ideally the comment for these three functions would be updated to
mention the PID argument.

Thanks,
Andrew