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

Message ID patch-14501-tamar@arm.com
State New
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Series
  • [Arm,gas] : Fix forward thumb references [PR gas/25235]
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Commit Message

Jan Beulich via Binutils May 25, 2021, 12:03 p.m.
Hi All,

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.

build on native hardware and regtested on
  arm-none-elf, arm-none-elf (32 bit host),
  arm-none-linux-gnueabihf, arm-none-linux-gnueabihf (32 bit host)

Cross-compiled and regtested on
  arm-none-linux-gnueabihf, armeb-none-elf, arm-wince-pe

and no issues.

Ok for master? and for backport to binutils-2.36?

Thanks,
Tamar

gas/ChangeLog:

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.

--- inline copy of patch -- 
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 9229dd081589228997a135117053697db049a370..1e2ac65d422cb7829cde5c9f03bcc57ef297e2c5 100644


--

Comments

Jan Beulich via Binutils May 25, 2021, 12:24 p.m. | #1
Hi Tamar,


> Ok for master? and for backport to binutils-2.36?


Approved for both.  Please apply.

Cheers
   Nick

Patch

diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 9229dd081589228997a135117053697db049a370..1e2ac65d422cb7829cde5c9f03bcc57ef297e2c5 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 0000000000000000000000000000000000000000..126950387014335afaf4a60b6292ab64cdd303f6
--- /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 0000000000000000000000000000000000000000..77637392f1c1b95e85ff2aeaf4a68507d4e466a9
--- /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
+