[MC][ARM] make Thumb function also if type attribute is set

Make sure to set the bottom bit of the symbol even when the type
attribute of a label is set after the label.

GNU as sets the thumb state according to the thumb state of the label.
If a .type directive is placed after the label, set the symbol's thumb
state according to the thumb state of the .type directive. This matches
GNU as in most cases.

From: Stefan Agner <stefan@agner.ch>

This fixes:
https://bugs.llvm.org/show_bug.cgi?id=44860
https://github.com/ClangBuiltLinux/linux/issues/866

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D74927

lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp

@@ -579,6 +579,28 @@ public:
     }
   }
 
+  /// If a label is defined before the .type directive sets the label's type
+  /// then the label can't be recorded as thumb function when the label is
+  /// defined. We override emitSymbolAttribute() which is called as part of the
+  /// parsing of .type so that if the symbol has already been defined we can
+  /// record the label as Thumb. FIXME: there is a corner case where the state
+  /// is changed in between the label definition and the .type directive, this
+  /// is not expected to occur in practice and handling it would require the
+  /// backend to track IsThumb for every label.
+  bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override {
+    bool Val = MCELFStreamer::emitSymbolAttribute(Symbol, Attribute);
+
+    if (!IsThumb)
+      return Val;
+
+    unsigned Type = cast<MCSymbolELF>(Symbol)->getType();
+    if ((Type == ELF::STT_FUNC || Type == ELF::STT_GNU_IFUNC) &&
+        Symbol->isDefined())
+      getAssembler().setIsThumbFunc(Symbol);
+
+    return Val;
+  };
+
 private:
   enum ElfMappingSymbol {
     EMS_None,

test/MC/ARM/thumb-function-address.s

@@ -0,0 +1,42 @@
+@ RUN: llvm-mc -filetype=obj -triple=armv7-linux-gnueabi %s -o %t
+@ RUN: llvm-readelf -s %t | FileCheck %s
+
+@@ GNU as sets the thumb state according to the thumb state of the label. If a
+@@ .type directive is placed after the label, set the symbol's thumb state
+@@ according to the thumb state of the .type directive. This matches GNU as in
+@@ most cases.
+
+.syntax unified
+.text
+.thumb
+func_label:
+.type func_label, %function
+
+.type foo_impl, %function
+foo_impl:
+  bx lr
+.type foo_resolver, %function
+foo_resolver:
+  b foo_impl
+.type foo, %gnu_indirect_function
+.set foo, foo_resolver
+
+@@ Note: GNU as sets the value to 1.
+.thumb
+label:
+  bx lr
+.arm
+  bx lr
+.type label, %function
+
+@@ Check func_label, foo_impl, foo_resolver, and foo addresses have bit 0 set.
+@@ Check label has bit 0 unset.
+@ CHECK:      Value Size Type   Bind  Vis     Ndx Name
+@ CHECK-NEXT: 00000000 0 NOTYPE LOCAL DEFAULT     UND
+@ CHECK-NEXT: 00000001 0 FUNC   LOCAL DEFAULT 2   func_label
+@ CHECK-NEXT: 00000001 0 FUNC   LOCAL DEFAULT 2   foo_impl
+@ CHECK-NEXT: 00000000 0 NOTYPE LOCAL DEFAULT 2   $t.0
+@ CHECK-NEXT: 00000003 0 FUNC   LOCAL DEFAULT 2   foo_resolver
+@ CHECK-NEXT: 00000003 0 IFUNC  LOCAL DEFAULT 2   foo
+@ CHECK-NEXT: 00000004 0 FUNC   LOCAL DEFAULT 2   label
+@ CHECK-NEXT: 00000006 0 NOTYPE LOCAL DEFAULT 2   $a.1