[PATCH v4] gdb: align siginfo_t with the Linux kernel definition

[PATCH v4] gdb: align siginfo_t with the Linux kernel definition

[Matthieu Longo]

GDB's current definition of siginfo_t is missing many fields present in
the Linux kernel definition [1].

These fields are useful for providing detailed, user-friendly diagnostics
when a fault occurs. Some new AArch64 extensions, such as Permission
Overlay Enhancement used to implement Protection Keys [2], require the
debugger to inspect 'si_pkey' alongside 'si_addr' to help the user identify
the problematic key.

This patch aligns GDB's definition of the __sifields._sigfault member of
siginfo_t with the definition from the Linux kernel master branch.

To avoid hardcoding the field access paths throughout the codebase, this
patch also introduces compile-time accessors for the siginfo_t attributes,
centralizing their definitions in a single location and making future
updates easier.

Finally, extend the testsuite to verify access to the new si_pkey field
and its preservation when modifying $_siginfo and when reading core files.
The tests in siginfo-obj.exp rely on the siginfo_t definition provided by
glibc's <signal.h>, which does not yet expose all of the fields present in
the kernel definition. As a result, the tests cannot exercise every newly
added field and therefore focus on si_pkey, the field motivating this change.
The test validates that GDB can read and modify the field correctly; it does
not attempt to generate a real protection-key fault.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
     tree/include/uapi/asm-generic/siginfo.h#n69
[2]: https://lore.kernel.org/all/20160212210213.ABC488FA@viggo.jf.intel.com/

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
---
 gdb/aarch64-linux-tdep.c               |  7 +--
 gdb/linux-tdep.c                       | 52 +++++++++++++++++++---
 gdb/linux-tdep.h                       | 60 ++++++++++++++++++++++++++
 gdb/sparc64-linux-tdep.c               |  5 ++-
 gdb/testsuite/gdb.base/siginfo-obj.c   |  1 +
 gdb/testsuite/gdb.base/siginfo-obj.exp | 14 ++++++
 6 files changed, 129 insertions(+), 10 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index f11eccc1bc1..705460312cf 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -2683,13 +2683,14 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
 
   try
     {
+      using gdb_si = gdb::siginfo_type;
       /* Sigcode tells us if the segfault is actually a memory tag
 	 violation.  */
-      si_code = parse_and_eval_long ("$_siginfo.si_code");
-      si_errno = parse_and_eval_long ("$_siginfo.si_errno");
+      si_code = parse_and_eval_long (gdb_si::get (gdb_si::key::si_code));
+      si_errno = parse_and_eval_long (gdb_si::get (gdb_si::key::si_errno));
 
       fault_addr
-	= parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
+	= parse_and_eval_long (gdb_si::get (gdb_si::key::si_addr));
     }
   catch (const gdb_exception_error &exception)
     {
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index 25d625db595..740043a9292 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -272,10 +272,9 @@ static struct type *
 linux_get_siginfo_type (struct gdbarch *gdbarch)
 {
   struct linux_gdbarch_data *linux_gdbarch_data;
-  struct type *void_ptr_type;
   struct type *uid_type, *pid_type;
   struct type *sigval_type, *clock_type;
-  struct type *siginfo_type, *sifields_type;
+  struct type *siginfo_type, *sifields_type, *sigfault_union_type;
   struct type *type;
 
   linux_gdbarch_data = get_linux_gdbarch_data (gdbarch);
@@ -285,11 +284,22 @@ linux_get_siginfo_type (struct gdbarch *gdbarch)
   type_allocator alloc (gdbarch);
 
   const struct builtin_type *builtin_types = builtin_type (gdbarch);
+  struct type *short_type = builtin_types->builtin_short;
   struct type *int_type = builtin_types->builtin_int;
   struct type *uint_type = builtin_types->builtin_unsigned_int;
   struct type *long_type = builtin_types->builtin_long;
-
-  void_ptr_type = lookup_pointer_type (builtin_type (gdbarch)->builtin_void);
+  struct type *unsigned_long_type = builtin_types->builtin_unsigned_long;
+  struct type *uint32_type = builtin_types->builtin_uint32;
+  struct type *void_ptr_type
+    = lookup_pointer_type (builtin_type (gdbarch)->builtin_void);
+
+  /* Compute padding length, i.e. __ADDR_BND_PKEY_PAD.  */
+  unsigned alignof_void_ptr = type_align (void_ptr_type);
+  unsigned padding_size = (alignof_void_ptr < short_type->length ()
+			   ? short_type->length ()
+			   : alignof_void_ptr);
+  struct type *addr_bnd_pkey_padding_type
+    = init_vector_type (builtin_types->builtin_uint8, padding_size);
 
   /* sival_t */
   sigval_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_UNION);
@@ -364,9 +374,41 @@ linux_get_siginfo_type (struct gdbarch *gdbarch)
   append_composite_type_field (type, "si_stime", clock_type);
   append_composite_type_field (sifields_type, "_sigchld", type);
 
-  /* _sigfault */
+  /* Begin _sigfault's anonymous union.  */
+  sigfault_union_type = arch_composite_type (gdbarch, NULL, TYPE_CODE_UNION);
+  /* used on alpha and sparc */
+  append_composite_type_field (sigfault_union_type, "si_trapno", int_type);
+  /* used when si_code is BUS_MCEERR_AR or BUS_MCEERR_AO.  */
+  append_composite_type_field (sigfault_union_type, "si_addr_lsb", short_type);
+
+  /* used when si_code=SEGV_BNDERR */
+  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
+  append_composite_type_field (type, "_dummy_bnd", addr_bnd_pkey_padding_type);
+  append_composite_type_field (type, "si_lower", void_ptr_type);
+  append_composite_type_field (type, "si_upper", void_ptr_type);
+  append_composite_type_field (sigfault_union_type, "_addr_bnd", type);
+
+  /* used when si_code=SEGV_PKUERR */
+  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
+  append_composite_type_field (type, "_dummy_pkey", addr_bnd_pkey_padding_type);
+  append_composite_type_field (type, "si_pkey", uint32_type);
+  append_composite_type_field (sigfault_union_type, "_addr_pkey", type);
+
+  /* used when si_code=TRAP_PERF */
+  type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
+  append_composite_type_field (type, "si_perf_data", unsigned_long_type);
+  append_composite_type_field (type, "si_perf_type", uint32_type);
+  append_composite_type_field (type, "si_perf_flags", uint32_type);
+  append_composite_type_field (sigfault_union_type, "_perf", type);
+
+  /* End _sigfault's anonymous union.  */
+
+  /* _sigfault is set by SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
   type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
   append_composite_type_field (type, "si_addr", void_ptr_type);
+  /* Since there is no possibility to declare an anonymous union,
+     using '_anon_union' instead.  */
+  append_composite_type_field (type, "_anon_union", sigfault_union_type);
   append_composite_type_field (sifields_type, "_sigfault", type);
 
   /* _sigpoll */
diff --git a/gdb/linux-tdep.h b/gdb/linux-tdep.h
index c19839fde2c..1dd0b3d2a17 100644
--- a/gdb/linux-tdep.h
+++ b/gdb/linux-tdep.h
@@ -98,4 +98,64 @@ extern CORE_ADDR linux_get_hwcap2 ();
 extern bool linux_address_in_shadow_stack_mem_range
   (CORE_ADDR addr, std::pair<CORE_ADDR, CORE_ADDR> *range);
 
+namespace gdb {
+
+/* Maps each siginfo_type::key to the corresponding field-access expression
+   in $_siginfo.
+
+   Keep the order of key values synchronized with the entries in get()'s
+   paths array.  Each key is used directly as an array index.  */
+
+struct siginfo_type
+{
+  /* Identifies a field within siginfo_t that may be referenced by name.  */
+  enum class key
+  {
+    si_signo = 0,
+    si_errno,
+    si_code,
+
+    /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
+    si_addr,
+    si_trapno,
+    si_addr_lsb,
+    si_lower,
+    si_upper,
+    si_pkey,
+    si_perf_data,
+    si_perf_type,
+    si_perf_flags,
+
+    /* Sentinel used to determine the number of mapped fields.  */
+    SI_ATTR_END
+  };
+
+  /* Return the $_siginfo access expression associated with ATTR_.
+
+     ATTR_ must be a valid si_* key other than SI_ATTR_END.  The array
+     order must exactly match the declaration order of the keys above.  */
+  static constexpr const char *get (key attr_)
+  {
+    const char *paths[static_cast<size_t> (key::SI_ATTR_END)] = {
+      "$_siginfo.si_signo",
+      "$_siginfo.si_errno",
+      "$_siginfo.si_code",
+
+      /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
+      "$_siginfo._sifields._sigfault.si_addr",
+      "$_siginfo._sifields._sigfault._anon_union.si_trapno",
+      "$_siginfo._sifields._sigfault._anon_union.si_addr_lsb",
+      "$_siginfo._sifields._sigfault._anon_union._addr_bnd.si_lower",
+      "$_siginfo._sifields._sigfault._anon_union._addr_bnd.si_upper",
+      "$_siginfo._sifields._sigfault._anon_union._addr_pkey.si_pkey",
+      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_data",
+      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_type",
+      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_flags",
+    };
+    return paths[static_cast<size_t> (attr_)];
+  }
+};
+
+} /* namespace gdb */
+
 #endif /* GDB_LINUX_TDEP_H */
diff --git a/gdb/sparc64-linux-tdep.c b/gdb/sparc64-linux-tdep.c
index cb7ce41e5cb..c4c4b8789f2 100644
--- a/gdb/sparc64-linux-tdep.c
+++ b/gdb/sparc64-linux-tdep.c
@@ -134,11 +134,12 @@ sparc64_linux_report_signal_info (struct gdbarch *gdbarch, struct ui_out *uiout,
 
   try
     {
+      using gdb_si = gdb::siginfo_type;
       /* Evaluate si_code to see if the segfault is ADI related.  */
-      si_code = parse_and_eval_long ("$_siginfo.si_code\n");
+      si_code = parse_and_eval_long (gdb_si::get (gdb_si::key::si_code));
 
       if (si_code >= SEGV_ACCADI && si_code <= SEGV_ADIPERR)
-	addr = parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
+	addr = parse_and_eval_long (gdb_si::get (gdb_si::key::si_addr));
     }
   catch (const gdb_exception_error &exception)
     {
diff --git a/gdb/testsuite/gdb.base/siginfo-obj.c b/gdb/testsuite/gdb.base/siginfo-obj.c
index 43dc979bc50..960e5b8e9cd 100644
--- a/gdb/testsuite/gdb.base/siginfo-obj.c
+++ b/gdb/testsuite/gdb.base/siginfo-obj.c
@@ -35,6 +35,7 @@ handler (int sig, siginfo_t *info, void *context)
   int ssi_signo = info->si_signo;
   int ssi_code = info->si_code;
   void *ssi_addr = info->si_addr;
+  unsigned int ssi_pkey = info->si_pkey;
 
   _exit (0); /* set breakpoint here */
 }
diff --git a/gdb/testsuite/gdb.base/siginfo-obj.exp b/gdb/testsuite/gdb.base/siginfo-obj.exp
index a94bf0e33ba..5e36b334068 100644
--- a/gdb/testsuite/gdb.base/siginfo-obj.exp
+++ b/gdb/testsuite/gdb.base/siginfo-obj.exp
@@ -78,6 +78,14 @@ gdb_test_multiple "p \$_siginfo" "$test" {
     }
 }
 
+set test "extract si_pkey"
+gdb_test_multiple "p \$_siginfo" "$test" {
+    -re "si_pkey = (\[0-9\]\+).*$gdb_prompt $" {
+	set ssi_pkey $expect_out(1,string)
+	pass "$test"
+    }
+}
+
 set bp_location [gdb_get_line_number "set breakpoint here"]
 
 with_test_prefix "validate siginfo fields" {
@@ -87,6 +95,7 @@ with_test_prefix "validate siginfo fields" {
     gdb_test "p ssi_errno" " = $ssi_errno"
     gdb_test "p ssi_code" " = $ssi_code"
     gdb_test "p ssi_signo" " = $ssi_signo"
+    gdb_test "p ssi_pkey" " = $ssi_pkey"
 }
 
 # Again, but this time, patch si_addr and check that the inferior sees
@@ -106,6 +115,7 @@ gdb_test "p \$_siginfo._sifields._sigfault.si_addr = 0x666" " = \\(void \\*\\) 0
 gdb_test "p \$_siginfo.si_errno = 666" " = 666"
 gdb_test "p \$_siginfo.si_code = 999" " = 999"
 gdb_test "p \$_siginfo.si_signo = 11" " = 11"
+gdb_test "p \$_siginfo._sifields._sigfault._anon_union._addr_pkey.si_pkey = 123" " = 123"
 
 with_test_prefix "validate modified siginfo fields" {
     gdb_test "break $bp_location"
@@ -114,6 +124,7 @@ with_test_prefix "validate modified siginfo fields" {
     gdb_test "p ssi_errno" " = 666"
     gdb_test "p ssi_code" " = 999"
     gdb_test "p ssi_signo" " = 11"
+    gdb_test "p ssi_pkey" " = 123"
 }
 
 # Test siginfo preservation in core files.
@@ -132,4 +143,7 @@ if {$gcore_created} {
     gdb_test "p \$_siginfo._sifields._sigfault.si_addr" \
 	" = \\(void \\*\\) $ssi_addr" \
 	"p \$_siginfo._sifields._sigfault.si_addr from core file"
+    gdb_test "p \$_siginfo._sifields._sigfault._anon_union._addr_pkey.si_pkey" \
+	" = $ssi_pkey" \
+	"p \$_siginfo._sifields._sigfault._anon_union._addr_pkey.si_pkey from core file"
 }
-- 
2.55.0

Re: [PATCH v4] gdb: align siginfo_t with the Linux kernel definition

[Matthieu Longo]

On 27/07/2026 15:08, Matthieu Longo wrote:
> diff --git a/gdb/linux-tdep.h b/gdb/linux-tdep.h
> index c19839fde2c..1dd0b3d2a17 100644
> --- a/gdb/linux-tdep.h
> +++ b/gdb/linux-tdep.h
> @@ -98,4 +98,64 @@ extern CORE_ADDR linux_get_hwcap2 ();
>  extern bool linux_address_in_shadow_stack_mem_range
>    (CORE_ADDR addr, std::pair<CORE_ADDR, CORE_ADDR> *range);
>  
> +namespace gdb {
> +
> +/* Maps each siginfo_type::key to the corresponding field-access expression
> +   in $_siginfo.
> +
> +   Keep the order of key values synchronized with the entries in get()'s
> +   paths array.  Each key is used directly as an array index.  */
> +
> +struct siginfo_type
> +{
> +  /* Identifies a field within siginfo_t that may be referenced by name.  */
> +  enum class key
> +  {
> +    si_signo = 0,
> +    si_errno,
> +    si_code,
> +
> +    /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
> +    si_addr,
> +    si_trapno,
> +    si_addr_lsb,
> +    si_lower,
> +    si_upper,
> +    si_pkey,
> +    si_perf_data,
> +    si_perf_type,
> +    si_perf_flags,
> +
> +    /* Sentinel used to determine the number of mapped fields.  */
> +    SI_ATTR_END
> +  };
> +

Thanks to Linaro's CI, I found a build issue in this patch.
Some of the enum names (si_addr) conflicts with macros defined in <signal.h> depending on the
version of Glibc installed on the machine I guess.
I could not reproduce the issue on my normal dev machine.

After the fix, the build passes and the macro values don't seem to conflict anymore with the enum
values.

Please let me know if you find a better solution to fix this build issue.
Note: renaming the enum values is an option, but then create inconsistencies with the names of
macros which I would prefer to be aligned.


  enum class key
  {
    si_signo = 0,
    si_errno,
    si_code,

    /* It seems that depending on the GLibc version and GCC version, macros
       in <signal.h> conflicts with some names in the enum. Hence all those
       push_macro and pop_macro.  Referencing those names later in the code
       does not seem to trigger a build issue.  */
#pragma push_macro("si_addr")
#undef si_addr
#pragma push_macro("si_addr_lsb")
#undef si_addr_lsb
#pragma push_macro("si_lower")
#undef si_lower
#pragma push_macro("si_upper")
#undef si_upper
#pragma push_macro("si_pkey")
#undef si_pkey
    /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
    si_addr,
    si_trapno,
    si_addr_lsb,
    si_lower,
    si_upper,
    si_pkey,
    si_perf_data,
    si_perf_type,
    si_perf_flags,
    si_tchange_target,
    si_tchange_type,
    si_tchange_flags,
#pragma pop_macro("si_addr")
#pragma pop_macro("si_addr_lsb")
#pragma pop_macro("si_lower")
#pragma pop_macro("si_upper")
#pragma pop_macro("si_pkey")

    /* Sentinel used to determine the number of mapped fields.  */
    SI_ATTR_END
  };

> +  /* Return the $_siginfo access expression associated with ATTR_.
> +
> +     ATTR_ must be a valid si_* key other than SI_ATTR_END.  The array
> +     order must exactly match the declaration order of the keys above.  */
> +  static constexpr const char *get (key attr_)
> +  {
> +    const char *paths[static_cast<size_t> (key::SI_ATTR_END)] = {
> +      "$_siginfo.si_signo",
> +      "$_siginfo.si_errno",
> +      "$_siginfo.si_code",
> +
> +      /* SIGILL, SIGFPE, SIGSEGV, SIGBUS, SIGTRAP, SIGEMT */
> +      "$_siginfo._sifields._sigfault.si_addr",
> +      "$_siginfo._sifields._sigfault._anon_union.si_trapno",
> +      "$_siginfo._sifields._sigfault._anon_union.si_addr_lsb",
> +      "$_siginfo._sifields._sigfault._anon_union._addr_bnd.si_lower",
> +      "$_siginfo._sifields._sigfault._anon_union._addr_bnd.si_upper",
> +      "$_siginfo._sifields._sigfault._anon_union._addr_pkey.si_pkey",
> +      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_data",
> +      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_type",
> +      "$_siginfo._sifields._sigfault._anon_union._perf.si_perf_flags",
> +    };
> +    return paths[static_cast<size_t> (attr_)];
> +  }
> +};
> +
> +} /* namespace gdb */
> +
>  #endif /* GDB_LINUX_TDEP_H */
Matthieu

Re: [PATCH v4] gdb: align siginfo_t with the Linux kernel definition

[Andreas Schwab]

On Jul 28 2026, Matthieu Longo wrote:

> Please let me know if you find a better solution to fix this build issue.
> Note: renaming the enum values is an option, but then create inconsistencies with the names of
> macros which I would prefer to be aligned.

<signal.h> reserves all identifiers beginning with si_.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: [PATCH v4] gdb: align siginfo_t with the Linux kernel definition

[Matthieu Longo]

On 28/07/2026 12:09, Andreas Schwab wrote:
> On Jul 28 2026, Matthieu Longo wrote:
> 
>> Please let me know if you find a better solution to fix this build issue.
>> Note: renaming the enum values is an option, but then create inconsistencies with the names of
>> macros which I would prefer to be aligned.
> 
> <signal.h> reserves all identifiers beginning with si_.
> 

I am going to publish a new revision taking this feedback into account.
Thanks Andreas.

Matthieu