[Bug gdb/31563] Problems with accessing errno

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31563

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vries at gcc dot gnu.org

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
FWIW, this:
...
diff --git a/gdb/infcall.c b/gdb/infcall.c
index 23d5652dd21..bf836c93152 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -1092,9 +1092,13 @@ call_function_by_hand_dummy (struct value *function,
     {
       const char *name = get_function_name (funaddr,
                                            name_buf, sizeof (name_buf));
-      error (_("'%s' has unknown return type; "
-              "cast the call to its declared return type"),
-            name);
+      if (gdbarch_osabi (gdbarch) == GDB_OSABI_LINUX
+         && strcmp (name, "__errno_location") == 0)
+       values_type = lookup_pointer_type (builtin_type
(gdbarch)->builtin_int);
+      else
+       error (_("'%s' has unknown return type; "
+                "cast the call to its declared return type"),
+              name);
     }

   values_type = check_typedef (values_type);
...
gives a few xpasses on the new test-case:
...
XPASS: gdb.base/check-errno.exp: macros: print errno
XPASS: gdb.base/check-errno.exp: macros: print (int) errno
XPASS: gdb.base/check-errno.exp: pthreads-macros: print errno
XPASS: gdb.base/check-errno.exp: pthreads-macros: print (int) errno
...

But it's still a bit hacky, in the sense that it doesn't fix ptype
__errno_location, in other words, it only has effect when doing an inferior
call.

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