[SFrame-V3] ld: testsuite: x86: sframe: check link of signal frame and outermost frames

In this test, two "special" case FDEs are linked:
  - Signal frame where the SFrame stack trace data is not
    representable.
  - _start like outermost frame function.

This is useful test for sframe_encoder's merge input sections
functionality and its associated write code-paths (sframe_encoder_write)
too.

ld/testsuite/
	* ld-x86-64/sframe-link-1.d: New test.
	* ld-x86-64/sframe-signal.s: New input file.
	* ld-x86-64/sframe-start.s: Likewise.
	* ld-x86-64/x86-64.exp: Add new test.

---
[Changes in V1]
  - Use register name in .cfi_* directives and clarify whats going on.
    [Jan].
[End of changes in V1]

[No changes in V2]

[Changes in V3]
  - Fixed some typos (respresentable, mimic'ing) [Indu].
  - Remove duplicate line in sframe-link-1.s [Indu].
[End of changes in V3]

ld/testsuite/ld-x86-64/sframe-link-1.d

@@ -0,0 +1,38 @@
+#as: --gsframe
+#source: sframe-start.s
+#source: sframe-signal.s
+#warning: \.cfi\_escape with op \(0xf\)
+#objdump: --sframe=.sframe
+#ld: -shared --no-rosegment -z separate-code
+#name: SFrame link special case FDEs - 1
+
+.*: +file format .*
+
+Contents of the SFrame section .sframe:
+  Header :
+
+    Version: SFRAME_VERSION_3
+    Flags: SFRAME_F_FDE_SORTED,
+           SFRAME_F_FDE_FUNC_START_PCREL
+    CFA fixed RA offset: \-8
+    Num FDEs: 4
+    Num FREs: 5
+
+  Function Index :
+
+    func idx \[0\]: pc = 0x1000, size = 16 bytes
+    STARTPC +CFA +FP +RA +
+    0+1000 +sp\+16 +u +f +
+    0+1006 +sp\+24 +u +f +
+
+    func idx \[1\]: pc = 0x1010, size = 16 bytes
+    STARTPC\[m\] +CFA +FP +RA +
+    0+0000 +sp\+8 +u +f +
+    0+000b +sp\+16 +u +f +
+
+    func idx \[2\]: pc = 0x1020, size = 8 bytes
+    STARTPC +CFA +FP +RA +
+    0+1020 +RA undefined
+
+    func idx \[3\]: pc = 0x1028, size = 2 bytes, attr = "S"
+    STARTPC +CFA +FP +RA +

ld/testsuite/ld-x86-64/sframe-signal.s

@@ -0,0 +1,18 @@
+# Input file with SFrame FDE for a signal trampoline
+# When linked with other "special" case FDEs like start frame,
+# this is a useful test for sframe_encoder's merge input sections
+# functionality and its associated write code-paths (sframe_encoder_write)
+	.text
+	.globl	rest_rt
+	.type	rest_rt, @function
+rest_rt:
+	.cfi_startproc
+	.cfi_signal_frame
+	# DW_CFA_def_cfa_expression, length, DW_OP_breg9, (sleb)offset, DW_OP_deref
+	.cfi_escape 0xf,0x3,0x79,0x78,0x6
+	nop
+	.cfi_offset rbp, -16
+	ret
+	.cfi_endproc
+	.size	rest_rt, .-rest_rt
+	.section	.note.GNU-stack,"",@progbits

ld/testsuite/ld-x86-64/sframe-start.s

@@ -0,0 +1,15 @@
+# Input file mimicking the start of frame FDE
+# When linked with other "special" case FDEs like signal frame,
+# this is a useful test for sframe_encoder's merge input sections
+# functionality and its associated write code-paths (sframe_encoder_write)
+	.text
+	.globl	_start
+	.type	_start, @function
+_start:
+	.cfi_startproc
+	.cfi_undefined rip
+	xor	%rbp, %rbp
+	call	foo
+	.cfi_endproc
+	.size	_start, .-_start
+	.section	.note.GNU-stack,"",@progbits

ld/testsuite/ld-x86-64/x86-64.exp

@@ -587,6 +587,7 @@ run_dump_test "tls-le-pic-3-x32"
 
 if { ![skip_sframe_tests] } {
     run_dump_test "sframe-simple-1"
+    run_dump_test "sframe-link-1"
     run_dump_test "sframe-command-line-1"
     run_dump_test "sframe-reloc-1"
     run_dump_test "sframe-plt-1"