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

4 files changed, 63 insertions, 0 deletions

diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index eb9bd9c..b27a7ec 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -229,6 +229,7 @@ if { [is_elf_format] } then {
     } else {
 	run_dump_test ifunc-1
 	run_elf_list_test "type" "" "" "-s" "| grep \"1 *\\\[FIONTCU\\\]\""
+	run_elf_list_test "type-2" "" "--warn" "-s" "| grep \"0 *\\\[FIONT\\\]\""
     }
 
     run_dump_test "section6"
diff --git a/gas/testsuite/gas/elf/type-2.e b/gas/testsuite/gas/elf/type-2.e
new file mode 100644
index 0000000..684727c
--- /dev/null
+++ b/gas/testsuite/gas/elf/type-2.e
@@ -0,0 +1,10 @@
+ +.+: 0+0 +0 +NOTYPE +LOCAL +DEFAULT +UND *
+ +.+: 0+0 +0 +OBJECT +LOCAL +DEFAULT +. test1
+ +.+: 0+1 +0 +FUNC +LOCAL +DEFAULT +. test2
+ +.+: 0+2 +0 +NOTYPE +LOCAL +DEFAULT +. test3
+ +.+: 0+3 +0 +NOTYPE +LOCAL +DEFAULT +. test4
+ +.+: 0+4 +0 +NOTYPE +LOCAL +DEFAULT +. test5
+ +.+: 0+5 +0 +NOTYPE +LOCAL +DEFAULT +. test6
+ +.+: 0+6 +0 +OBJECT +LOCAL +DEFAULT +. test7
+ +.+: 0+7 +0 +TLS +LOCAL +DEFAULT +. test8
+ +.+: 0+8 +0 +IFUNC +LOCAL +DEFAULT +. test9
diff --git a/gas/testsuite/gas/elf/type-2.l b/gas/testsuite/gas/elf/type-2.l
new file mode 100644
index 0000000..f4c626e
--- /dev/null
+++ b/gas/testsuite/gas/elf/type-2.l
@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*:4: Warning: .*
+.*:9: Warning: .*
diff --git a/gas/testsuite/gas/elf/type-2.s b/gas/testsuite/gas/elf/type-2.s
new file mode 100644
index 0000000..c0a28eb
--- /dev/null
+++ b/gas/testsuite/gas/elf/type-2.s
@@ -0,0 +1,49 @@
+	.text
+
+	.type	test1,%function
+	.type	test1,%object
+test1:
+	.byte	0x0
+
+	.type	test2,%object
+	.type	test2,%function
+test2:
+	.byte	0x0
+
+	.type	test3,%object
+	.type	test3,%notype
+test3:
+	.byte	0x0
+
+	.type	test4,%function
+	.type	test4,%notype
+test4:
+	.byte	0x0
+
+	.type	test5,%tls_object
+	.type	test5,%notype
+test5:
+	.byte	0x0
+
+	.type	test6,%gnu_indirect_function
+	.type	test6,%notype
+test6:
+	.byte	0x0
+
+	.type	test7,%function
+	.type	test7,%notype
+	.type	test7,%object
+test7:
+	.byte	0x0
+
+	.type	test8,%object
+	.type	test8,%tls_object
+	.type	test8,%object
+test8:
+	.byte	0x0
+
+	.type	test9,%function
+	.type	test9,%gnu_indirect_function
+	.type	test9,%function
+test9:
+	.byte	0x0