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

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

On 9/8/22 07:41, Thiago Jung Bauermann via Gdb-patches wrote:
> 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
> thread_info parameter seems more correct than setting current_thread in one
> particular code path.
> 
> Changes are propagated to allow passing the thread parameter through the
> call chain.

I suppose the effects will only be known when later patches are applied. But the auxv data is per-process, right?

It sounds a bit strange to pass a thread for the hwcap/auxv lookup. Is there some other reason to do that?

> ---
>   gdbserver/linux-aarch64-low.cc |  6 +++---
>   gdbserver/linux-arm-low.cc     |  2 +-
>   gdbserver/linux-low.cc         | 20 +++++++++++---------
>   gdbserver/linux-low.h          | 10 +++++-----
>   gdbserver/linux-ppc-low.cc     |  6 +++---
>   gdbserver/linux-s390-low.cc    |  2 +-
>   gdbserver/netbsd-low.cc        |  4 ++--
>   gdbserver/netbsd-low.h         |  4 ++--
>   gdbserver/server.cc            |  2 +-
>   gdbserver/target.cc            |  4 ++--
>   gdbserver/target.h             |  4 ++--
>   11 files changed, 33 insertions(+), 31 deletions(-)
> 
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index db5086962612..5d4d667dfa42 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -826,9 +826,9 @@ aarch64_target::low_arch_setup ()
>   
>         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 (current_thread, 8) & AARCH64_HWCAP_PACA;
>         /* A-profile MTE is 64-bit only.  */
> -      features.mte = linux_get_hwcap2 (8) & HWCAP2_MTE;
> +      features.mte = linux_get_hwcap2 (current_thread, 8) & HWCAP2_MTE;
>         features.tls = true;
>   
>         current_process ()->tdesc = aarch64_linux_read_description (features);
> @@ -3299,7 +3299,7 @@ aarch64_target::supports_memory_tagging ()
>   #endif
>       }
>   
> -  return (linux_get_hwcap2 (8) & HWCAP2_MTE) != 0;
> +  return (linux_get_hwcap2 (current_thread, 8) & HWCAP2_MTE) != 0;
>   }
>   
>   bool
> diff --git a/gdbserver/linux-arm-low.cc b/gdbserver/linux-arm-low.cc
> index ab6209a3abc8..d40ce412fe1c 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, 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 2f71360d3bde..9034a1d8fabe 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -5486,12 +5486,12 @@ 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 (const thread_info *thread, CORE_ADDR offset,
> +				 unsigned char *myaddr, unsigned int len)
>   {
>     char filename[PATH_MAX];
>     int fd, n;
> -  int pid = lwpid_of (current_thread);
> +  int pid = lwpid_of (thread);
>   
>     xsnprintf (filename, sizeof filename, "/proc/%d/auxv", pid);
>   
> @@ -6912,14 +6912,16 @@ 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 (const thread_info *thread, 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 (thread, offset, data, 2 * wordsize)
> +	 == 2 * wordsize)
>       {
>         if (wordsize == 4)
>   	{
> @@ -6949,20 +6951,20 @@ 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 (const thread_info *thread, int wordsize)
>   {
>     CORE_ADDR hwcap = 0;
> -  linux_get_auxv (wordsize, AT_HWCAP, &hwcap);
> +  linux_get_auxv (thread, wordsize, AT_HWCAP, &hwcap);
>     return hwcap;
>   }
>   
>   /* See linux-low.h.  */
>   
>   CORE_ADDR
> -linux_get_hwcap2 (int wordsize)
> +linux_get_hwcap2 (const thread_info *thread, int wordsize)
>   {
>     CORE_ADDR hwcap2 = 0;
> -  linux_get_auxv (wordsize, AT_HWCAP2, &hwcap2);
> +  linux_get_auxv (thread, wordsize, AT_HWCAP2, &hwcap2);
>     return hwcap2;
>   }
>   
> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
> index 79be31b8f729..bd1ec31dc5a4 100644
> --- a/gdbserver/linux-low.h
> +++ b/gdbserver/linux-low.h
> @@ -178,8 +178,8 @@ class linux_process_target : public process_stratum_target
>   
>     bool supports_read_auxv () override;
>   
> -  int read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> -		 unsigned int len) override;
> +  int read_auxv (const thread_info *thread, CORE_ADDR offset,
> +		 unsigned char *myaddr, unsigned int len) override;
>   
>     int insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
>   		    int size, raw_breakpoint *bp) override;
> @@ -944,17 +944,17 @@ 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,
> +int linux_get_auxv (const thread_info *thread, 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 (const thread_info *thread, 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 (const thread_info *thread, int wordsize);
>   
>   #endif /* GDBSERVER_LINUX_LOW_H */
> diff --git a/gdbserver/linux-ppc-low.cc b/gdbserver/linux-ppc-low.cc
> index 08824887003b..08608b2dcc38 100644
> --- a/gdbserver/linux-ppc-low.cc
> +++ b/gdbserver/linux-ppc-low.cc
> @@ -894,8 +894,8 @@ ppc_target::low_arch_setup ()
>   
>     /* The value of current_process ()->tdesc needs to be set for this
>        call.  */
> -  ppc_hwcap = linux_get_hwcap (features.wordsize);
> -  ppc_hwcap2 = linux_get_hwcap2 (features.wordsize);
> +  ppc_hwcap = linux_get_hwcap (current_thread, features.wordsize);
> +  ppc_hwcap2 = linux_get_hwcap2 (current_thread, features.wordsize);
>   
>     features.isa205 = ppc_linux_has_isa205 (ppc_hwcap);
>   
> @@ -1097,7 +1097,7 @@ is_elfv2_inferior (void)
>     const struct target_desc *tdesc = current_process ()->tdesc;
>     int wordsize = register_size (tdesc, 0);
>   
> -  if (!linux_get_auxv (wordsize, AT_PHDR, &phdr))
> +  if (!linux_get_auxv (current_thread, wordsize, AT_PHDR, &phdr))
>       return def_res;
>   
>     /* Assume ELF header is at the beginning of the page where program headers
> diff --git a/gdbserver/linux-s390-low.cc b/gdbserver/linux-s390-low.cc
> index 5adc28070574..0d01dffa64a4 100644
> --- a/gdbserver/linux-s390-low.cc
> +++ b/gdbserver/linux-s390-low.cc
> @@ -592,7 +592,7 @@ s390_target::low_arch_setup ()
>     /* Determine word size and HWCAP.  */
>     int pid = pid_of (current_thread);
>     int wordsize = s390_get_wordsize (pid);
> -  unsigned long hwcap = linux_get_hwcap (wordsize);
> +  unsigned long hwcap = linux_get_hwcap (current_thread, wordsize);
>   
>     /* Check whether the kernel supports extra register sets.  */
>     int have_regset_last_break
> diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
> index f05bcd4e173f..71ac61e9dfbd 100644
> --- a/gdbserver/netbsd-low.cc
> +++ b/gdbserver/netbsd-low.cc
> @@ -581,10 +581,10 @@ netbsd_read_auxv(pid_t pid, void *offs, void *addr, size_t len)
>      to debugger memory starting at MYADDR.  */
>   
>   int
> -netbsd_process_target::read_auxv (CORE_ADDR offset,
> +netbsd_process_target::read_auxv (const thread_info *thread, CORE_ADDR offset,
>   				  unsigned char *myaddr, unsigned int len)
>   {
> -  pid_t pid = pid_of (current_thread);
> +  pid_t pid = pid_of (thread);
>   
>     return netbsd_read_auxv (pid, (void *) (intptr_t) offset, myaddr, len);
>   }
> diff --git a/gdbserver/netbsd-low.h b/gdbserver/netbsd-low.h
> index 06b4fd613571..506329251eaf 100644
> --- a/gdbserver/netbsd-low.h
> +++ b/gdbserver/netbsd-low.h
> @@ -77,8 +77,8 @@ class netbsd_process_target : public process_stratum_target
>   
>     bool supports_read_auxv () override;
>   
> -  int read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> -		 unsigned int len) override;
> +  int read_auxv (const thread_info *thread, CORE_ADDR offset,
> +		 unsigned char *myaddr, unsigned int len) override;
>   
>     bool supports_hardware_single_step () override;
>   
> diff --git a/gdbserver/server.cc b/gdbserver/server.cc
> index c619206d5d2d..2d5cf6e8d8de 100644
> --- a/gdbserver/server.cc
> +++ b/gdbserver/server.cc
> @@ -1443,7 +1443,7 @@ handle_qxfer_auxv (const char *annex,
>     if (annex[0] != '\0' || current_thread == NULL)
>       return -1;
>   
> -  return the_target->read_auxv (offset, readbuf, len);
> +  return the_target->read_auxv (current_thread, offset, readbuf, len);
>   }
>   
>   /* Handle qXfer:exec-file:read.  */
> diff --git a/gdbserver/target.cc b/gdbserver/target.cc
> index adcfe6e7bcc7..7ee18bde8635 100644
> --- a/gdbserver/target.cc
> +++ b/gdbserver/target.cc
> @@ -344,8 +344,8 @@ process_stratum_target::supports_read_auxv ()
>   }
>   
>   int
> -process_stratum_target::read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> -				   unsigned int len)
> +process_stratum_target::read_auxv (const thread_info *thread, CORE_ADDR offset,
> +				   unsigned char *myaddr, unsigned int len)
>   {
>     gdb_assert_not_reached ("target op read_auxv not supported");
>   }
> diff --git a/gdbserver/target.h b/gdbserver/target.h
> index 6c536a307786..cd6b2193a228 100644
> --- a/gdbserver/target.h
> +++ b/gdbserver/target.h
> @@ -175,8 +175,8 @@ class process_stratum_target
>     /* Read auxiliary vector data from the inferior process.
>   
>        Read LEN bytes at OFFSET into a buffer at MYADDR.  */
> -  virtual int read_auxv (CORE_ADDR offset, unsigned char *myaddr,
> -			 unsigned int len);
> +  virtual int read_auxv (const thread_info *thread, CORE_ADDR offset,
> +			 unsigned char *myaddr, unsigned int len);
>   
>     /* Returns true if GDB Z breakpoint type TYPE is supported, false
>        otherwise.  The type is coded as follows: