Arm: Fix forward thumb references [PR gas/25235]

When assembling a forward reference the symbol will be unknown and so during
do_t_adr we cannot set the thumb bit.  The bit it set so early to prevent
relaxations that are invalid. i.e. relaxing a Thumb2 to Thumb1 insn when the
symbol is Thumb.

But because it's done so early we miss the case for forward references.
This patch changes it so that we additionally check the thumb bit during the
internal relocation processing.

In principle we should be able to only set the bit during reloc processing but
that would require changes to the other relocations that the instruction could
be relaxed to.

This approach still allows early relaxations (which means that we have less
iteration of internal reloc processing) while still fixing the forward reference
case.

gas/ChangeLog:

2021-05-24  Tamar Christina  <tamar.christina@arm.com>

	PR gas/25235
	* config/tc-arm.c (md_convert_frag): Set LSB when Thumb symbol.
	(relax_adr): Thumb symbols 4 bytes.
	* testsuite/gas/arm/pr25235.d: New test.
	* testsuite/gas/arm/pr25235.s: New test.

4 files changed, 72 insertions, 1 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index bc7a00f..45cce1b 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,11 @@
+2021-05-25  Tamar Christina  <tamar.christina@arm.com>
+
+	PR gas/25235
+	* config/tc-arm.c (md_convert_frag): Set LSB when Thumb symbol.
+	(relax_adr): Thumb symbols 4 bytes.
+	* testsuite/gas/arm/pr25235.d: New test.
+	* testsuite/gas/arm/pr25235.s: New test.
+
 2021-05-24  Nelson Chu  <nelson.chu@sifive.com>
 
 	PR 25212
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 9229dd0..1e2ac65 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -26827,6 +26827,14 @@ md_convert_frag (bfd *abfd, segT asec ATTRIBUTE_UNUSED, fragS *fragp)
       pc_rel = (opcode == T_MNEM_ldr_pc2);
       break;
     case T_MNEM_adr:
+      /* Thumb bits should be set in the frag handling so we process them
+	 after all symbols have been seen.  PR gas/25235.  */
+      if (exp.X_op == O_symbol
+	  && exp.X_add_symbol != NULL
+	  && S_IS_DEFINED (exp.X_add_symbol)
+	  && THUMB_IS_FUNC (exp.X_add_symbol))
+	exp.X_add_number |= 1;
+
       if (fragp->fr_var == 4)
 	{
 	  insn = THUMB_OP32 (opcode);
@@ -27024,7 +27032,8 @@ relax_adr (fragS *fragp, asection *sec, long stretch)
   if (fragp->fr_symbol == NULL
       || !S_IS_DEFINED (fragp->fr_symbol)
       || sec != S_GET_SEGMENT (fragp->fr_symbol)
-      || S_IS_WEAK (fragp->fr_symbol))
+      || S_IS_WEAK (fragp->fr_symbol)
+      || THUMB_IS_FUNC (fragp->fr_symbol))
     return 4;
 
   val = relaxed_symbol_addr (fragp, stretch);
diff --git a/gas/testsuite/gas/arm/pr25235.d b/gas/testsuite/gas/arm/pr25235.d
new file mode 100644
index 0000000..1269503
--- /dev/null
+++ b/gas/testsuite/gas/arm/pr25235.d
@@ -0,0 +1,24 @@
+#skip: *-*-pe *-*-wince *-*-vxworks
+#objdump: -dr
+#name: PR25235: Thumb forward references error
+
+.*: +file format .*arm.*
+
+Disassembly of section .text:
+
+00000000 <f1>:
+   0:	46c0      	nop			; \(mov r8, r8\)
+   2:	46c0      	nop			; \(mov r8, r8\)
+
+00000004 <f2>:
+   4:	f2af 0107 	subw	r1, pc, #7
+   8:	f20f 0305 	addw	r3, pc, #5
+   c:	a401      	add	r4, pc, #4	; \(adr r4, 14 <f4>\)
+   e:	46c0      	nop			; \(mov r8, r8\)
+
+00000010 <f3>:
+  10:	46c0      	nop			; \(mov r8, r8\)
+  12:	46c0      	nop			; \(mov r8, r8\)
+
+00000014 <f4>:
+  14:	e1a00000 	nop			; \(mov r0, r0\)
diff --git a/gas/testsuite/gas/arm/pr25235.s b/gas/testsuite/gas/arm/pr25235.s
new file mode 100644
index 0000000..7763739
--- /dev/null
+++ b/gas/testsuite/gas/arm/pr25235.s
@@ -0,0 +1,30 @@
+    .syntax unified
+    .thumb
+
+    .align 2
+    .type f1, %function
+    .thumb_func
+    f1:
+        nop
+
+    .align 2
+    .type f2, %function
+    .thumb_func
+    f2:
+        adr r1, f1
+        adr r3, f3
+        adr r4, f4
+
+
+    .align 2
+    .type f3, %function
+    .thumb_func
+    f3:
+        nop
+
+    .align 2
+    .type f3, %function
+    .arm
+    f4:
+        nop
+