[Patch, Arm, Gas] Add unwinder encoding support for PACBTI.

[Patch, Arm, Gas] Add unwinder encoding support for PACBTI.

[Tejas Belagod]

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Hi,

This patch adds support for encoding the Return Address Authentication pseudo register - '.save {ra_auth_code}' as defined by the DWARF ABI (https://github.com/ARM-software/abi-aa/releases/download/2021Q1/aadwarf32.pdf Section 4.1) - in the exception tables where the opcode is defined by the EHABI (https://github.com/ARM-software/abi-aa/releases/download/2021Q1/ehabi32.pdf Section 10.3).

Tested on arm-none-eabi. Ok for master?

Thanks,
Tejas.

gas/Changelog:

2021-10-05  Tejas Belagod  <tejas.belagod@arm.com>

	* config/tc-arm.c (arm_reg_type): Add new type REG_TYPE_PSEUDO.
	(reg_expected_msgs): Add message for pseudo reg type.
	(reg_list_els): Add new reg list type REGLIST_PSEUDO.
	(parse_reg_list): Handle new REGLIST_PSEUDO type.
	(s_arm_unwind_save_pseudo): Encode pseudo reg list save in exception
	tables.
	(s_arm_unwind_save): Handle new REG_TYPE_PSEUDO.
	(reg_names): Add ra_auth_code pseudo register.
	* testsuite/gas/arm/unwind-pacbti-m.s: New test.
	* testsuite/gas/arm/unwind-pacbti-m.d: New test.
	* testsuite/gas/arm/unwind-pacbti-m-readelf.d: New test.

[-- Attachment #2: ra_auth_code.txt --]
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diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index d288d8d1573e8bda9d39cc9232313ae12e21066a..d7ff2b56b7db98decc3f2660e5c5d203ff885224 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -688,7 +688,8 @@ enum arm_reg_type
   REG_TYPE_MMXWCG,
   REG_TYPE_XSCALE,
   REG_TYPE_RNB,
-  REG_TYPE_ZR
+  REG_TYPE_ZR,
+  REG_TYPE_PSEUDO
 };
 
 /* Structure for a hash table entry for a register.
@@ -733,6 +734,7 @@ const char * const reg_expected_msgs[] =
   [REG_TYPE_MQ]	    = N_("MVE vector register expected"),
   [REG_TYPE_RNB]    = "",
   [REG_TYPE_ZR]     = N_("ZR register expected"),
+  [REG_TYPE_PSEUDO] = N_("Pseudo register expected"),
 };
 
 /* Some well known registers that we refer to directly elsewhere.  */
@@ -1893,6 +1895,7 @@ parse_scalar (char **ccp, int elsize, struct neon_type_el *type, enum
 enum reg_list_els
 {
   REGLIST_RN,
+  REGLIST_PSEUDO,
   REGLIST_CLRM,
   REGLIST_VFP_S,
   REGLIST_VFP_S_VPR,
@@ -1910,7 +1913,8 @@ parse_reg_list (char ** strp, enum reg_list_els etype)
   long range = 0;
   int another_range;
 
-  gas_assert (etype == REGLIST_RN || etype == REGLIST_CLRM);
+  gas_assert (etype == REGLIST_RN || etype == REGLIST_CLRM
+	      || etype == REGLIST_PSEUDO);
 
   /* We come back here if we get ranges concatenated by '+' or '|'.  */
   do
@@ -1930,8 +1934,14 @@ parse_reg_list (char ** strp, enum reg_list_els etype)
 	      int reg;
 	      const char apsr_str[] = "apsr";
 	      int apsr_str_len = strlen (apsr_str);
+	      enum arm_reg_type rt;
 
-	      reg = arm_reg_parse (&str, REG_TYPE_RN);
+	      if (etype == REGLIST_RN || etype == REGLIST_CLRM)
+		rt = REG_TYPE_RN;
+	      else
+		rt = REG_TYPE_PSEUDO;
+
+	      reg = arm_reg_parse (&str, rt);
 	      if (etype == REGLIST_CLRM)
 		{
 		  if (reg == REG_SP || reg == REG_PC)
@@ -1950,6 +1960,14 @@ parse_reg_list (char ** strp, enum reg_list_els etype)
 		      return FAIL;
 		    }
 		}
+	      else if (etype == REGLIST_PSEUDO)
+		{
+		  if (reg == FAIL)
+		    {
+		      first_error (_(reg_expected_msgs[REG_TYPE_PSEUDO]));
+		      return FAIL;
+		    }
+		}
 	      else /* etype == REGLIST_RN.  */
 		{
 		  if (reg == FAIL)
@@ -4258,6 +4276,32 @@ s_arm_unwind_personality (int ignored ATTRIBUTE_UNUSED)
   demand_empty_rest_of_line ();
 }
 
+/* Parse a directive saving pseudo registers.  */
+
+static void
+s_arm_unwind_save_pseudo (void)
+{
+  valueT op;
+  long range;
+
+  range = parse_reg_list (&input_line_pointer, REGLIST_PSEUDO);
+  if (range == FAIL)
+    {
+      as_bad (_("expected pseudo register list"));
+      ignore_rest_of_line ();
+      return;
+    }
+
+  demand_empty_rest_of_line ();
+
+  if (range & (1 << 9))
+    {
+      /* Opcode for restoring RA_AUTH_CODE.  */
+      op = 0xb4;
+      add_unwind_opcode (op, 1);
+    }
+}
+
 
 /* Parse a directive saving core registers.  */
 
@@ -4725,6 +4769,10 @@ s_arm_unwind_save (int arch_v6)
       s_arm_unwind_save_core ();
       return;
 
+    case REG_TYPE_PSEUDO:
+      s_arm_unwind_save_pseudo ();
+      return;
+
     case REG_TYPE_VFD:
       if (arch_v6)
 	s_arm_unwind_save_vfp_armv6 ();
@@ -23915,8 +23963,12 @@ static const struct reg_entry reg_names[] =
   /* XScale accumulator registers.  */
   REGNUM(acc,0,XSCALE), REGNUM(ACC,0,XSCALE),
 
-  /* Alias 'ra_auth_code' to r12 for pacbti.  */
-  REGDEF(ra_auth_code,12,RN),
+  /* DWARF ABI defines RA_AUTH_CODE to 143. It also reserves 134-142 for future
+     expansion.  RA_AUTH_CODE here is given the value 143 % 134 to make it easy
+     for tc_arm_regname_to_dw2regnum to translate to DWARF reg number using
+     134 + reg_number should the range 134 to 142 be used for more pseudo regs
+     in the future.  This also helps fit RA_AUTH_CODE into a bitmask.  */
+  REGDEF(ra_auth_code,9,PSEUDO),
 };
 #undef REGDEF
 #undef REGNUM
diff --git a/gas/testsuite/gas/arm/unwind-pacbti-m-readelf.d b/gas/testsuite/gas/arm/unwind-pacbti-m-readelf.d
new file mode 100644
index 0000000000000000000000000000000000000000..ba1d76dd18fbe0ca2c391c12ddcb180d1de3b32b
--- /dev/null
+++ b/gas/testsuite/gas/arm/unwind-pacbti-m-readelf.d
@@ -0,0 +1,16 @@
+#readelf: -u
+#source: unwind-pacbti-m.s
+#name: Unwind table information for Armv8.1-M.Mainline PACBTI extension
+# This test is only valid on ELF based ports.
+#notarget: *-*-pe *-*-wince
+# VxWorks needs a special variant of this file.
+#skip: *-*-vxworks*
+
+Unwind section '.ARM.exidx' at offset 0x40 contains 1 entry:
+
+0x0 <foo>: 0x80b4a8b0
+  Compact model index: 0
+  0xb4      pop {ra_auth_code}
+  0xa8      pop {r4, r14}
+  0xb0      finish
+
diff --git a/gas/testsuite/gas/arm/unwind-pacbti-m.d b/gas/testsuite/gas/arm/unwind-pacbti-m.d
new file mode 100644
index 0000000000000000000000000000000000000000..584b12037b30136decb15da75a3e2641bd010827
--- /dev/null
+++ b/gas/testsuite/gas/arm/unwind-pacbti-m.d
@@ -0,0 +1,23 @@
+#objdump: -sr
+#name: Unwind information for Armv8.1-M.Mainline PACBTI extension
+# This test is only valid on ELF based ports.
+#notarget: *-*-pe *-*-wince
+# VxWorks needs a special variant of this file.
+#skip: *-*-vxworks*
+
+.*:     file format.*
+
+RELOCATION RECORDS FOR \[.ARM.exidx\]:
+OFFSET   TYPE              VALUE 
+00000000 R_ARM_PREL31      .text
+00000000 R_ARM_NONE        __aeabi_unwind_cpp_pr0
+
+
+Contents of section .text:
+ 0000 10b54df8 04cd5df8 04cb10bd  .*
+Contents of section .ARM.exidx:
+ 0000 00000000 b0a8b480  .*
+Contents of section .ARM.attributes:
+ 0000 41290000 00616561 62690001 1f000000  .*
+ 0010 05382e31 2d4d2e4d 41494e00 0615074d  .*
+ 0020 09033202 34024a01 4c01               .*
diff --git a/gas/testsuite/gas/arm/unwind-pacbti-m.s b/gas/testsuite/gas/arm/unwind-pacbti-m.s
new file mode 100644
index 0000000000000000000000000000000000000000..5a6ea2eec2b8e48dd49963f0a4b93fa29c3c3a49
--- /dev/null
+++ b/gas/testsuite/gas/arm/unwind-pacbti-m.s
@@ -0,0 +1,20 @@
+
+	.arch armv8.1-m.main
+	.arch_extension pacbti
+	.eabi_attribute 50, 2
+	.eabi_attribute 52, 2
+	.eabi_attribute 74, 1
+	.eabi_attribute 76, 1
+	.text
+	.syntax unified
+	.thumb
+	.thumb_func
+foo:
+	.fnstart
+	push	{r4, lr}
+	.save {r4, lr}
+	push	{r12}
+	.save {ra_auth_code}
+	pop	{r12}
+	pop	{r4, pc}
+	.fnend

Re: [Patch, Arm, Gas] Add unwinder encoding support for PACBTI.

[Nick Clifton]

Hi Tejas,

> 2021-10-05  Tejas Belagod  <tejas.belagod@arm.com>
> 
> 	* config/tc-arm.c (arm_reg_type): Add new type REG_TYPE_PSEUDO.
> 	(reg_expected_msgs): Add message for pseudo reg type.
> 	(reg_list_els): Add new reg list type REGLIST_PSEUDO.
> 	(parse_reg_list): Handle new REGLIST_PSEUDO type.
> 	(s_arm_unwind_save_pseudo): Encode pseudo reg list save in exception
> 	tables.
> 	(s_arm_unwind_save): Handle new REG_TYPE_PSEUDO.
> 	(reg_names): Add ra_auth_code pseudo register.
> 	* testsuite/gas/arm/unwind-pacbti-m.s: New test.
> 	* testsuite/gas/arm/unwind-pacbti-m.d: New test.
> 	* testsuite/gas/arm/unwind-pacbti-m-readelf.d: New test.

Approved - please apply.

Cheers
   Nick