[gdb] Fix warning in foreach_arch selftests

When running the selftests, I run into:
...
$ gdb -q -batch -ex "maint selftest"
  ...
Running selftest execute_cfa_program::aarch64:ilp32.
warning: A handler for the OS ABI "GNU/Linux" is not built into this
configuration of GDB.  Attempting to continue with the default aarch64:ilp32
settings.
...
and likewise for execute_cfa_program::i8086 and
execute_cfa_program::ia64-elf32.

The warning can easily be reproduced outside the selftests by doing:
...
$ gdb -q -batch -ex "set arch aarch64:ilp32"
...
and can be prevented by first doing "set osabi none".

Fix the warning by setting osabi to none while doing selftests that iterate
over all architectures.

This causes a regression in the print_one_insn selftests for the ARC
architecture.

The problem is pre-existing, and can be demonstrated (already without this
patch) using:
...
$ gdb -q -batch -ex "set osabi none" -ex "maint selftest print_one_insn::A6"
Running selftest print_one_insn::A6.
Self test failed: Cannot access memory at address 0x0
Ran 1 unit tests, 1 failed
$
...

For ARC, we use the generic case in print_one_insn_test, containing this code:
...
       int kind = gdbarch_breakpoint_kind_from_pc (gdbarch, &pc);
       ...
       insn = gdbarch_sw_breakpoint_from_kind (gdbarch, kind, &bplen);
...

The problem is that with osabi linux we trigger:
...
static int
arc_linux_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *pcptr)
{
  return trap_size;
}
...
but with osabi none:
...
arc_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *pcptr)
{
  size_t length_with_limm = gdb_insn_length (gdbarch, *pcptr);
...
which needs access to memory, and will consequently fail.

Fix this in print_one_insn_test, in the default case, by iterating over
supported osabi's to makes sure we trigger arc_linux_breakpoint_kind_from_pc
which will give us a usable instruction to disassemble.

Tested on x86_64-linux.

gdb/disasm-selftests.c

@@ -101,12 +101,52 @@ print_one_insn_test (struct gdbarch *gdbarch)
       {
 	/* Test disassemble breakpoint instruction.  */
 	CORE_ADDR pc = 0;
-	int kind = gdbarch_breakpoint_kind_from_pc (gdbarch, &pc);
+	int kind;
 	int bplen;
 
-	insn = gdbarch_sw_breakpoint_from_kind (gdbarch, kind, &bplen);
-	len = bplen;
+	struct gdbarch_info info;
+	info.bfd_arch_info = gdbarch_bfd_arch_info (gdbarch);
 
+	enum gdb_osabi it;
+	bool found = false;
+	for (it = GDB_OSABI_UNKNOWN; it != GDB_OSABI_INVALID;
+	     it = static_cast<enum gdb_osabi>(static_cast<int>(it) + 1))
+	  {
+	    if (it == GDB_OSABI_UNKNOWN)
+	      continue;
+
+	    info.osabi = it;
+
+	    if (it != GDB_OSABI_NONE)
+	      {
+		if (!has_gdb_osabi_handler (info))
+		  /* Unsupported.  Skip to prevent warnings like:
+		     A handler for the OS ABI <x> is not built into this
+		     configuration of GDB.  Attempting to continue with the
+		     default <y> settings.  */
+		  continue;
+	      }
+
+	    gdbarch = gdbarch_find_by_info (info);
+	    SELF_CHECK (gdbarch != NULL);
+
+	    try
+	      {
+		kind = gdbarch_breakpoint_kind_from_pc (gdbarch, &pc);
+		insn = gdbarch_sw_breakpoint_from_kind (gdbarch, kind, &bplen);
+	      }
+	    catch (...)
+	      {
+		continue;
+	      }
+	    found = true;
+	    break;
+	  }
+
+	/* Assert that we have found an instruction to disassemble.  */
+	SELF_CHECK (found);
+
+	len = bplen;
 	break;
       }
     }

gdb/osabi.c

@@ -332,9 +332,10 @@ can_run_code_for (const struct bfd_arch_info *a, const struct bfd_arch_info *b)
   return (a == b || a->compatible (a, b) == a);
 }
 
+/* Return OS ABI handler for INFO.  */
 
-void
-gdbarch_init_osabi (struct gdbarch_info info, struct gdbarch *gdbarch)
+static struct gdb_osabi_handler *
+gdbarch_osabi_handler (struct gdbarch_info info)
 {
   struct gdb_osabi_handler *handler;
 
@@ -367,10 +368,32 @@ gdbarch_init_osabi (struct gdbarch_info info, struct gdbarch *gdbarch)
 	 ISA").  BFD doesn't normally consider 32-bit and 64-bit
 	 "compatible" so it doesn't succeed.  */
       if (can_run_code_for (info.bfd_arch_info, handler->arch_info))
-	{
-	  (*handler->init_osabi) (info, gdbarch);
-	  return;
-	}
+	return handler;
+    }
+
+  return nullptr;
+}
+
+/* See osabi.h.  */
+
+bool
+has_gdb_osabi_handler (struct gdbarch_info info)
+{
+  return gdbarch_osabi_handler (info) != nullptr;
+}
+
+void
+gdbarch_init_osabi (struct gdbarch_info info, struct gdbarch *gdbarch)
+{
+  struct gdb_osabi_handler *handler;
+
+  gdb_assert (info.osabi != GDB_OSABI_UNKNOWN);
+  handler = gdbarch_osabi_handler (info);
+
+  if (handler != nullptr)
+    {
+      (*handler->init_osabi) (info, gdbarch);
+      return;
     }
 
   if (info.osabi == GDB_OSABI_NONE)

gdb/osabi.h

@@ -74,6 +74,9 @@ enum gdb_osabi gdbarch_lookup_osabi (bfd *);
    string.  */
 enum gdb_osabi osabi_from_tdesc_string (const char *text);
 
+/* Return true if there's an OS ABI handler for INFO.  */
+bool has_gdb_osabi_handler (struct gdbarch_info info);
+
 /* Initialize the gdbarch for the specified OS ABI variant.  */
 void gdbarch_init_osabi (struct gdbarch_info, struct gdbarch *);
 

gdb/selftest-arch.c

@@ -68,6 +68,7 @@ foreach_arch_test_generator (const std::string &name,
 	   {
 	     struct gdbarch_info info;
 	     info.bfd_arch_info = bfd_scan_arch (arch);
+	     info.osabi = GDB_OSABI_NONE;
 	     struct gdbarch *gdbarch = gdbarch_find_by_info (info);
 	     SELF_CHECK (gdbarch != NULL);
 	     function (gdbarch);