[SFrame-V3] gas: sframe: testsuite: handle .cfi_offset for RA

With the introduction of flex FDE type, handling .cfi_offset for
RA needs adjustment.

On architectures like x86_64, the return address (RA) is typically saved
at a fixed offset from the CFA. Previous versions of the SFrame format
assumed this fixed offset was invariant for the entire function on such
architectures. Consequently, GAS would warn and suppress SFrame
generation if it encountered a .cfi_offset directive for the RA
register that deviated from this fixed default.

SFrame V3 introduces "Flex FDEs" which allows tracking the RA location
explicitly even on architectures where it is usually fixed.

This patch updates sframe_xlate_do_offset () to leverage Flex FDEs. When
processing a .cfi_offset for the RA register:
  - The check for non-representable RA offsets is relaxed. If the ABI
    supports Flex FDEs (SFrame V3), GAS proceeds instead of issuing a
    warning.
  - For ABIs without explicit RA tracking (like AMD64), if the RA
    offset differs from the default fixed offset, the FDE is marked as a
    Flex FDE, and the new stack location is recorded.
  - Logic is added to detect when the RA is restored to its standard
    fixed offset. In this case, the tracking state is reset (ra_loc set
    to SFRAME_FRE_ELEM_LOC_NONE), deferring to the ABI's default fixed RA
    offset behavior.

gas/
	* gen-sframe.c (sframe_xlate_do_offset): Support .cfi_offset for RA
	by switching to Flex FDEs when necessary.
gas/testsuite/
	* gas/cfi-sframe/cfi-sframe-x86_64-6.d: New test.
	* gas/cfi-sframe/cfi-sframe-x86_64-6.s: New test to check
	transition of location of REG_RA from register to CFA-8 (default
	location on AMD64).  Flex FDE in effect.
	* gas/cfi-sframe/cfi-sframe.exp: Add new test.

gas/gen-sframe.c

@@ -1393,8 +1393,10 @@ sframe_xlate_do_offset (struct sframe_xlate_ctx *xlate_ctx,
 
   /* For ABIs not tracking RA, the return address is expected to be in a
      specific location.  Explicit manourvering to a different offset (than the
-     default offset) is non-representable in SFrame.  */
-  if (!sframe_ra_tracking_p () && cfi_insn->u.ri.reg == SFRAME_CFA_RA_REG
+     default offset) is non-representable in SFrame, unless flex FDE generation
+     is supported for the ABI.  */
+  if (!sframe_support_flex_fde_p () && !sframe_ra_tracking_p ()
+      && cfi_insn->u.ri.reg == SFRAME_CFA_RA_REG
       && cfi_insn->u.ri.offset != sframe_cfa_ra_offset ())
     {
       as_warn (_("no SFrame FDE emitted; %s register %u in .cfi_offset"),
@@ -1412,16 +1414,35 @@ sframe_xlate_do_offset (struct sframe_xlate_ctx *xlate_ctx,
       cur_fre->fp_deref_p = true;
       cur_fre->merge_candidate = false;
     }
-  else if (sframe_ra_tracking_p ()
-	   && cfi_insn->u.ri.reg == SFRAME_CFA_RA_REG)
+  /* Either the ABI has enabled RA tracking, in which case we must process the
+     DW_CFA_offset opcode for REG_RA like usual.  Or if the ABI has not enabled
+     RA tracking, but flex FDE generation is supported, distinguish between
+     whether its time to reset the RA tracking state or not.  */
+  else if (cfi_insn->u.ri.reg == SFRAME_CFA_RA_REG)
     {
-      sframe_fre_set_ra_track (cur_fre, cfi_insn->u.ri.offset);
-      cur_fre->ra_reg = SFRAME_FRE_REG_INVALID;
-      cur_fre->ra_deref_p = true;
-      cur_fre->merge_candidate = false;
+      if (!sframe_ra_tracking_p ()
+	  && cfi_insn->u.ri.offset == sframe_cfa_ra_offset ())
+	{
+	  /* Reset RA tracking info, if fixed offset.  */
+	  cur_fre->ra_reg = SFRAME_FRE_REG_INVALID;
+	  cur_fre->ra_loc = SFRAME_FRE_ELEM_LOC_NONE;
+	  cur_fre->ra_deref_p = false;
+	  cur_fre->merge_candidate = false;
+	}
+      else
+	{
+	  sframe_fre_set_ra_track (cur_fre, cfi_insn->u.ri.offset);
+	  cur_fre->ra_reg = SFRAME_FRE_REG_INVALID;
+	  cur_fre->ra_loc = SFRAME_FRE_ELEM_LOC_STACK;
+	  cur_fre->ra_deref_p = true;
+	  cur_fre->merge_candidate = false;
+
+	  if (!sframe_ra_tracking_p () && sframe_support_flex_fde_p ())
+	    xlate_ctx->flex_p = true;
+	}
     }
-  /* This is used to track changes to non-rsp registers, skip all others
-     except FP / RA for now.  */
+
+  /* Skip all other registers.  */
   return SFRAME_XLATE_OK;
 }
 

gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-6.d

@@ -0,0 +1,25 @@
+#as: --gsframe
+#objdump: --sframe=.sframe
+#name: Flex FDE with RA state transition
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_3
+    Flags: SFRAME_F_FDE_FUNC_START_PCREL
+    CFA fixed RA offset: \-8
+    Num FDEs: 1
+    Num FREs: 5
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x0, size = 16 bytes, attr = "F"
+    STARTPC +CFA +FP +RA +
+    0+0000 +sp\+8 +u +f +
+    0+0004 +sp\+40 +u +f +
+    0+0008 +sp\+40 +u +r3\+0 +
+    0+000b +sp\+40 +u +f +
+    0+000f +sp\+8 +u +f +
+
+#pass

gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-6.s

@@ -0,0 +1,16 @@
+# Testcase for transition of tracked entity (rip) from
+# register to CFA+offset.
+	.type	foo, @function
+foo:
+	.cfi_startproc
+	sub	$0x20,%rsp
+	.cfi_adjust_cfa_offset 0x20
+	.long 0
+	.cfi_register rip, 3
+	mov %rax, %rdi
+	.cfi_offset rip, -8
+	.long 0
+	.cfi_def_cfa rsp, 8
+	ret
+	.cfi_endproc
+	.size	foo, .-foo

gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-7.d

@@ -0,0 +1,25 @@
+#as: --gsframe
+#objdump: --sframe=.sframe
+#name: Flex FDE with RA state transition 2
+#...
+Contents of the SFrame section .sframe:
+
+  Header :
+
+    Version: SFRAME_VERSION_3
+    Flags: SFRAME_F_FDE_FUNC_START_PCREL
+    CFA fixed RA offset: \-8
+    Num FDEs: 1
+    Num FREs: 5
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x0, size = 20 bytes, attr = "F"
+    STARTPC +CFA +FP +RA +
+    0+0000 +sp\+8 +u +f +
+    0+0004 +sp\+40 +u +f +
+    0+000b +sp\+40 +u +c-16 +
+    0+000f +sp\+8 +u +c-16 +
+    0+0013 +sp\+8 +u +f +
+
+#pass

gas/testsuite/gas/cfi-sframe/cfi-sframe-x86_64-7.s

@@ -0,0 +1,17 @@
+# Testcase for creation of flex FDE for offset divergence from fixed offset on
+# AMD64
+	.type	foo, @function
+foo:
+	.cfi_startproc
+	sub	$0x20,%rsp
+	.cfi_adjust_cfa_offset 0x20
+	.long 0
+	mov	%rax, %rdi
+	.cfi_offset rip, -16
+	.long 0
+	.cfi_def_cfa rsp, 8
+	.long 0
+	.cfi_offset rip, -8
+	ret
+	.cfi_endproc
+	.size	foo, .-foo

gas/testsuite/gas/cfi-sframe/cfi-sframe.exp

@@ -63,6 +63,8 @@ if { [istarget "x86_64-*-*"] && [gas_sframe_check] } then {
 	run_dump_test "cfi-sframe-x86_64-3"
 	run_dump_test "cfi-sframe-x86_64-4"
 	run_dump_test "cfi-sframe-x86_64-5"
+	run_dump_test "cfi-sframe-x86_64-6"
+	run_dump_test "cfi-sframe-x86_64-7"
 	run_dump_test "cfi-sframe-x86_64-esc-expr-1"
 	run_dump_test "cfi-sframe-x86_64-esc-expr-2"
 	run_dump_test "cfi-sframe-x86_64-esc-expr-3"