gas/ELF: don't accumulate .type settings

Recently a patch was submitted for a Xen Project test harness binary to
override the compiler specified @object to @func (see [1]). In a reply I
suggested we shouldn't make ourselves dependent on currently unspecified
behavior of gas here: It accumulates all requests, and then
bfd/elf.c:swap_out_syms(), in an apparently ad hoc manner, prioritizes
certain flags over others.

Make the behavior predictable: Generally the last .type is what counts.
Exceptions are directives which set multiple bits (TLS, IFUNC, and
UNIQUE): Subsequent directives requesting just the more generic bit
(i.e. FUNC following IFUNC) won't clear the more specific one.  Warn
about incompatible changes, except from/to STT_NOTYPE.

Also add a new target hook, which hppa wants to use right away afaict.

In the course of adding the warning I ran into two ld testsuite
failures.  I can only assume that it was a copy-and-paste mistake that
lead to the same symbol having its type set twice.

[1] https://lists.xenproject.org/archives/html/xen-devel/2019-05/msg01980.html

1 files changed, 32 insertions, 1 deletions

diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index 318e27d..224d4c2 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -2069,7 +2069,38 @@ obj_elf_type (int ignore ATTRIBUTE_UNUSED)
   if (*input_line_pointer == '"')
     ++input_line_pointer;
 
-  elfsym->symbol.flags |= type;
+#ifdef md_elf_symbol_type_change
+  if (!md_elf_symbol_type_change (sym, elfsym, type))
+#endif
+    {
+      flagword mask = BSF_FUNCTION | BSF_OBJECT;
+
+      if (type != BSF_FUNCTION)
+	mask |= BSF_GNU_INDIRECT_FUNCTION;
+      if (type != BSF_OBJECT)
+	{
+	  mask |= BSF_GNU_UNIQUE | BSF_THREAD_LOCAL;
+
+	  if (S_IS_COMMON (sym))
+	    {
+	      as_bad (_("cannot change type of common symbol '%s'"),
+		      S_GET_NAME (sym));
+	      mask = type = 0;
+	    }
+	}
+
+      /* Don't warn when changing to STT_NOTYPE.  */
+      if (type)
+	{
+	  flagword new = (elfsym->symbol.flags & ~mask) | type;
+
+	  if (new != (elfsym->symbol.flags | type))
+	    as_warn (_("symbol '%s' already has its type set"), S_GET_NAME (sym));
+	  elfsym->symbol.flags = new;
+	}
+      else
+	elfsym->symbol.flags &= ~mask;
+    }
 
   demand_empty_rest_of_line ();
 }