[PATCH v1] 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.

[1]: https://github.com/torvalds/linux/blob/2b414a95b8f7307d42173ba9e580d6
     d3e2bcbfce/include/uapi/asm-generic/siginfo.h#L69-L100
[2]: https://lore.kernel.org/all/20160212210213.ABC488FA@viggo.jf.intel.com/
---
 gdb/linux-tdep.c | 39 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index a7381677498..5baad41a083 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -275,7 +275,7 @@ linux_get_siginfo_type (struct gdbarch *gdbarch)
   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);
@@ -285,9 +285,12 @@ 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;
+  struct type *unsigned_long_type = builtin_types->builtin_unsigned_long;
+  struct type *uint32_type = builtin_types->builtin_uint32;
 
   void_ptr_type = lookup_pointer_type (builtin_type (gdbarch)->builtin_void);
 
@@ -364,9 +367,41 @@ 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=BUS_MCEERR_AR or used when si_code=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", short_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", short_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 possiblity to declare an anonymous union,
+     using '_' instead.  */
+  append_composite_type_field (type, "_", sigfault_union_type);
   append_composite_type_field (sifields_type, "_sigfault", type);
 
   /* _sigpoll */
-- 
2.54.0