gdb/riscv: Support c.li in prologue unwinder

I was seeing some failures in gdb.threads/omp-par-scope.exp when run
on a riscv64 target.  It turns out the cause of the problem is that I
didn't have debug information installed for libgomp.so, which this
test makes use of.  The test requires GDB to backtrace through a
libgomp function, and the riscv prologue unwinder was failing to
unwind this particular stack frame.

The reason for the failure to unwind was that the function prologue
includes a c.li (compressed load immediate) instruction, and the riscv
prologue scanning unwinder doesn't know what to do with this
instruction, though the unwinder does understand c.lui (compressed
load unsigned immediate).

This commit adds support for c.li.  After this GDB is able to unwind
through libgomp, and I no longer see any unexpected failures in
gdb.threads/omp-par-scope.exp.

I've also included a new test in gdb.arch/ which specifically checks
for our c.li support.

1 files changed, 29 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.arch/riscv64-unwind-prologue-with-c_li.c b/gdb/testsuite/gdb.arch/riscv64-unwind-prologue-with-c_li.c
new file mode 100644
index 0000000..d3a0cb3
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/riscv64-unwind-prologue-with-c_li.c
@@ -0,0 +1,29 @@
+/* Copyright 2023 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/>.  */
+
+/* See riscv64-unwind-prologue-with-c_li-asm.s.  */
+extern int foo (void);
+
+int
+bar (void)
+{
+  return 0;
+}
+
+int
+main (void)
+{
+  return foo ();
+}