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

[Matthieu Longo <matthieu.longo@arm.com>]

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