[PATCH v1] gdb/linux: add helpers to read AT_HWCAP3 and AT_HWCAP4

[PATCH v1] gdb/linux: add helpers to read AT_HWCAP3 and AT_HWCAP4

[Matthieu Longo]

Add linux_get_hwcap3 and linux_get_hwcap4 helpers to GDB and gdbserver,
mirroring the existing linux_get_hwcap and linux_get_hwcap2 interfaces.

The new helpers retrieve the AT_HWCAP3 and AT_HWCAP4 auxiliary vector
entry either from explicitly supplied auxv data or from the current
inferior.

This prepares for future features that depend on HWCAP3 and HWCAP4
capability bits.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
---
 gdb/linux-tdep.c       | 38 ++++++++++++++++++++++++++++++++++++++
 gdb/linux-tdep.h       | 22 ++++++++++++++++++++++
 gdbserver/linux-low.cc | 28 ++++++++++++++++++++++++++++
 gdbserver/linux-low.h  |  8 ++++++++
 4 files changed, 96 insertions(+)

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index 30a279248ec..a11427edf61 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -3215,6 +3215,44 @@ linux_get_hwcap2 ()
 			   current_inferior ()->arch ());
 }
 
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap3 (const std::optional<gdb::byte_vector> &auxv,
+		  target_ops *target, gdbarch *gdbarch)
+{
+  return linux_get_hwcap_helper (auxv, target, gdbarch, AT_HWCAP3);
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap3 ()
+{
+  return linux_get_hwcap3 (target_read_auxv (),
+			   current_inferior ()->top_target (),
+			   current_inferior ()->arch ());
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap4 (const std::optional<gdb::byte_vector> &auxv,
+		  target_ops *target, gdbarch *gdbarch)
+{
+  return linux_get_hwcap_helper (auxv, target, gdbarch, AT_HWCAP4);
+}
+
+/* See linux-tdep.h.  */
+
+CORE_ADDR
+linux_get_hwcap4 ()
+{
+  return linux_get_hwcap4 (target_read_auxv (),
+			   current_inferior ()->top_target (),
+			   current_inferior ()->arch ());
+}
+
 /* Display whether the gcore command is using the
    /proc/PID/coredump_filter file.  */
 
diff --git a/gdb/linux-tdep.h b/gdb/linux-tdep.h
index 1dd0b3d2a17..8f7e7aafbd0 100644
--- a/gdb/linux-tdep.h
+++ b/gdb/linux-tdep.h
@@ -91,6 +91,28 @@ extern CORE_ADDR linux_get_hwcap2 (const std::optional<gdb::byte_vector> &auxv,
 
 extern CORE_ADDR linux_get_hwcap2 ();
 
+/* Fetch the AT_HWCAP3 entry from auxv data AUXV.  Use TARGET and GDBARCH to
+   parse auxv entries.
+
+   On error, 0 is returned.  */
+extern CORE_ADDR linux_get_hwcap3 (const std::optional<gdb::byte_vector> &auxv,
+				   struct target_ops *target, gdbarch *gdbarch);
+
+/* Same as the above, but obtain all the inputs from the current inferior.  */
+
+extern CORE_ADDR linux_get_hwcap3 ();
+
+/* Fetch the AT_HWCAP4 entry from auxv data AUXV.  Use TARGET and GDBARCH to
+   parse auxv entries.
+
+   On error, 0 is returned.  */
+extern CORE_ADDR linux_get_hwcap4 (const std::optional<gdb::byte_vector> &auxv,
+				   struct target_ops *target, gdbarch *gdbarch);
+
+/* Same as the above, but obtain all the inputs from the current inferior.  */
+
+extern CORE_ADDR linux_get_hwcap4 ();
+
 /* Returns true if ADDR belongs to a shadow stack memory range.  If this
    is the case, assign the shadow stack memory range to RANGE
    [start_address, end_address).  */
diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index f1be62225e2..c4daba0bf40 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -70,6 +70,14 @@
 #define AT_HWCAP2 26
 #endif
 
+#ifndef AT_HWCAP3
+#define AT_HWCAP3 29
+#endif
+
+#ifndef AT_HWCAP4
+#define AT_HWCAP4 30
+#endif
+
 /* Some targets did not define these ptrace constants from the start,
    so gdbserver defines them locally here.  In the future, these may
    be removed after they are added to asm/ptrace.h.  */
@@ -7235,6 +7243,26 @@ linux_get_hwcap2 (int pid, int wordsize)
   return hwcap2;
 }
 
+/* See linux-low.h.  */
+
+CORE_ADDR
+linux_get_hwcap3 (int pid, int wordsize)
+{
+  CORE_ADDR hwcap3 = 0;
+  linux_get_auxv (pid, wordsize, AT_HWCAP3, &hwcap3);
+  return hwcap3;
+}
+
+/* See linux-low.h.  */
+
+CORE_ADDR
+linux_get_hwcap4 (int pid, int wordsize)
+{
+  CORE_ADDR hwcap4 = 0;
+  linux_get_auxv (pid, wordsize, AT_HWCAP4, &hwcap4);
+  return hwcap4;
+}
+
 #ifdef HAVE_LINUX_REGSETS
 void
 initialize_regsets_info (struct regsets_info *info)
diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
index 60154240ddd..b274d3cb370 100644
--- a/gdbserver/linux-low.h
+++ b/gdbserver/linux-low.h
@@ -977,4 +977,12 @@ CORE_ADDR linux_get_hwcap (int pid, int wordsize);
 
 CORE_ADDR linux_get_hwcap2 (int pid, int wordsize);
 
+/* Fetch the AT_HWCAP3 entry from the auxv vector, where entries are length
+   WORDSIZE, of process with pid PID.  If no entry was found, return 0.  */
+CORE_ADDR linux_get_hwcap3 (int pid, int wordsize);
+
+/* Fetch the AT_HWCAP4 entry from the auxv vector, where entries are length
+   WORDSIZE, of process with pid PID.  If no entry was found, return 0.  */
+CORE_ADDR linux_get_hwcap4 (int pid, int wordsize);
+
 #endif /* GDBSERVER_LINUX_LOW_H */
-- 
2.55.0

Re: [PATCH v1] gdb/linux: add helpers to read AT_HWCAP3 and AT_HWCAP4

[Matthieu Longo]

On 27/07/2026 18:28, Matthieu Longo wrote:
> Add linux_get_hwcap3 and linux_get_hwcap4 helpers to GDB and gdbserver,
> mirroring the existing linux_get_hwcap and linux_get_hwcap2 interfaces.
> 
> The new helpers retrieve the AT_HWCAP3 and AT_HWCAP4 auxiliary vector
> entry either from explicitly supplied auxv data or from the current
> inferior.
> 
> This prepares for future features that depend on HWCAP3 and HWCAP4
> capability bits.
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Ping.

Re: [PATCH v1] gdb/linux: add helpers to read AT_HWCAP3 and AT_HWCAP4

[Simon Marchi]

On 7/27/26 1:28 PM, Matthieu Longo wrote:
> Add linux_get_hwcap3 and linux_get_hwcap4 helpers to GDB and gdbserver,
> mirroring the existing linux_get_hwcap and linux_get_hwcap2 interfaces.
> 
> The new helpers retrieve the AT_HWCAP3 and AT_HWCAP4 auxiliary vector
> entry either from explicitly supplied auxv data or from the current
> inferior.
> 
> This prepares for future features that depend on HWCAP3 and HWCAP4
> capability bits.
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

LGTM

Approved-By: Simon Marchi <simon.marchi@efficios.com>

But one question that picked my curiosity:

> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index f1be62225e2..c4daba0bf40 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -70,6 +70,14 @@
>  #define AT_HWCAP2 26
>  #endif
>  
> +#ifndef AT_HWCAP3
> +#define AT_HWCAP3 29
> +#endif
> +
> +#ifndef AT_HWCAP4
> +#define AT_HWCAP4 30
> +#endif

How come we need to provide these values in gdbserver, but not in the
equivalent native part of gdb?

Simon

Re: [PATCH v1] gdb/linux: add helpers to read AT_HWCAP3 and AT_HWCAP4

[Matthieu Longo]

On 20/08/2026 15:29, Simon Marchi wrote:
> On 7/27/26 1:28 PM, Matthieu Longo wrote:
>> Add linux_get_hwcap3 and linux_get_hwcap4 helpers to GDB and gdbserver,
>> mirroring the existing linux_get_hwcap and linux_get_hwcap2 interfaces.
>>
>> The new helpers retrieve the AT_HWCAP3 and AT_HWCAP4 auxiliary vector
>> entry either from explicitly supplied auxv data or from the current
>> inferior.
>>
>> This prepares for future features that depend on HWCAP3 and HWCAP4
>> capability bits.
>>
>> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> 
> LGTM
> 
> Approved-By: Simon Marchi <simon.marchi@efficios.com>
> 

Thanks !

> But one question that picked my curiosity:
> 
>> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
>> index f1be62225e2..c4daba0bf40 100644
>> --- a/gdbserver/linux-low.cc
>> +++ b/gdbserver/linux-low.cc
>> @@ -70,6 +70,14 @@
>>  #define AT_HWCAP2 26
>>  #endif
>>  
>> +#ifndef AT_HWCAP3
>> +#define AT_HWCAP3 29
>> +#endif
>> +
>> +#ifndef AT_HWCAP4
>> +#define AT_HWCAP4 30
>> +#endif
> 
> How come we need to provide these values in gdbserver, but not in the
> equivalent native part of gdb?
> 
> Simon

Those values had already been added in elf/common.h by this patch:
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=0c90306549b02dd2b07fe3f2639ab3ac75a29558

Matthieu