[PATCH] gdb/testsuite: Add test to step through function epilogue

[Bruno Larsen <blarsen@redhat.com>]

The testsuite implicitly tests GDB's ability to step through epilogues
in multiple tests, without doing it explicitly anywhere.  This is
unfortunate, as clang does not emit epilogue information, so using clang
on our testsuite makes many tests fail.  This patch adds a central,
explicit test for walking through the epilogue so we can safely remove
this from other tests and have them working with clang.

The test created attempts to step through a simple empilogue, an
epilogue that ends on another epilogue, and epilogues leading to other
function calls.
---
 .../gdb.base/step-through-epilogue.c          | 15 ++++
 .../gdb.base/step-through-epilogue.exp        | 86 +++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 gdb/testsuite/gdb.base/step-through-epilogue.c
 create mode 100644 gdb/testsuite/gdb.base/step-through-epilogue.exp

diff --git a/gdb/testsuite/gdb.base/step-through-epilogue.c b/gdb/testsuite/gdb.base/step-through-epilogue.c
new file mode 100644
index 00000000000..3e0ea5a2522
--- /dev/null
+++ b/gdb/testsuite/gdb.base/step-through-epilogue.c
@@ -0,0 +1,15 @@
+int multiply (int a, int b){
+    return a*b;
+}
+
+int square (int x){
+    return multiply (x, x);
+}
+
+int main(){
+    int x;
+    x = multiply (1,2);
+    x = square(2);
+    x = multiply (square (1), square (2));
+    return 0;
+}
diff --git a/gdb/testsuite/gdb.base/step-through-epilogue.exp b/gdb/testsuite/gdb.base/step-through-epilogue.exp
new file mode 100644
index 00000000000..762623cf72c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/step-through-epilogue.exp
@@ -0,0 +1,86 @@
+#   Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This test is used to confirm that GDB is able to step, stopping at an
+# epilogue line, then step out of the function.
+
+standard_testfile
+
+if { [get_compiler_info "clang-*"] } {
+    untested "This test can't be used with clang"
+    return
+}
+
+if { [prepare_for_testing "failed to prepare" "skip" \
+			  {step-through-epilogue.c}] } {
+    untested "failed to prepare"
+    return
+}
+
+if { ![runto_main] } {
+    untested "couldn't run to main"
+    return
+}
+
+# Some gcc versions, at least 6.5.0 and 9.2.0, can mess this test by
+# requiring extra steps in a few locations.  We test here and use
+# this knowledge later to decide if the extra steps need to be taken.
+set slow_gcc 0
+if { [test_compiler_info "gcc-6-5-0"] || [test_compiler_info "gcc-9-2-0"]} {
+    set slow_gcc 1
+}
+
+proc step_till_epilogue_multiply {} {
+    gdb_test "step" ".*return a.b;.*" "step into multiply"
+    gdb_test "step" ".*3\\s+\\\}.*" "stop at the epilogue of multiply"
+}
+
+proc step_till_epilogue_square {} {
+    gdb_test "step" ".*return multiply.*" "step into square"
+    step_till_epilogue_multiply
+    gdb_test "step" ".*7\\s+\\\}.*" "stop at epilogue of square"
+}
+
+with_test_prefix "multiply" {
+    step_till_epilogue_multiply
+    gdb_test "step" ".*x = square\\(2\\);" "leave function"
+}
+
+with_test_prefix "square" {
+    step_till_epilogue_square
+    gdb_test "step" ".*x = multiply \\(square \\(1\\), square \\(2\\)\\);.*"\
+	"leave function"
+}
+
+with_test_prefix "square, first argument" {
+    step_till_epilogue_square
+    if {$slow_gcc} {
+	gdb_test "step"\
+	    ".*x = multiply \\(square \\(1\\), square \\(2\\)\\);.*"\
+	    "step back to main"
+    }
+}
+with_test_prefix "square, second argument" {
+    step_till_epilogue_square
+    if {$slow_gcc} {
+	gdb_test "step"\
+	    ".*x = multiply \\(square \\(1\\), square \\(2\\)\\);.*"\
+	    "step back to main"
+    }
+}
+with_test_prefix "multiply with function args" {
+    step_till_epilogue_multiply
+    gdb_test "step" ".*return 0;.*" "leave last function"
+}
-- 
2.31.1