RISC-V: Fix elfutils testsuite unwind failures.

The clone.S patch fixes 2 elfutils testsuite unwind failures, where the
backtrace gets stuck repeating __thread_start until we hit the backtrace
limit.  This was confirmed by building and installing a patched glibc and
then building elfutils and running its testsuite.

Unfortunately, the testcase isn't working as expected and I don't know why.
The testcase passes even when my clone.S patch is not installed.  The testcase
looks logically similarly to the elfutils testcases that are failing.  Maybe
there is a subtle difference in how the glibc unwinding works versus the
elfutils unwinding?  I don't have good gdb pthread support yet, so I haven't
found a way to debug this.  Anyways, I don't know if the testcase is useful or
not.  If the testcase isn't useful then maybe the clone.S patch is OK without
a testcase?

Jim

	[BZ #24040]
	* elf/Makefile (CFLAGS-tst-unwind-main.c): Add -DUSE_PTHREADS=0.
	* elf/tst-unwind-main.c: If USE_PTHEADS, include pthread.h and error.h
	(func): New.
	(main): If USE_PTHREADS, call pthread_create to run func.  Otherwise
	call func directly.
	* nptl/Makefile (tests): Add tst-unwind-thread.
	(CFLAGS-tst-unwind-thread.c): Define.
	* nptl/tst-unwind-thread.c: New file.
	* sysdeps/unix/sysv/linux/riscv/clone.S (__thread_start): Mark ra
	as undefined.

1 files changed, 5 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/riscv/clone.S b/sysdeps/unix/sysv/linux/riscv/clone.S
index c079c1fb9f..0ff9ab3fd9 100644
--- a/sysdeps/unix/sysv/linux/riscv/clone.S
+++ b/sysdeps/unix/sysv/linux/riscv/clone.S
@@ -69,6 +69,11 @@ L (error):
 
 ENTRY (__thread_start)
 L (thread_start):
+	/* Terminate call stack by noting ra is undefined.  Use a dummy
+	   .cfi_label to force starting the FDE.  */
+	.cfi_label .Ldummy
+	cfi_undefined (ra)
+
 	/* Restore the arg for user's function.  */
 	REG_L		a1,0(sp)	/* Function pointer.  */
 	REG_L		a0,SZREG(sp)	/* Argument pointer.  */