From 9b2329f66cfcee3e43b5a0a4ca2bfa02e9a1fb51 Mon Sep 17 00:00:00 2001
From: Michael Matz <matz@suse.de>
Date: Wed, 15 Jul 2020 23:11:42 +0200
Subject: [PATCH] riscv64: Work around qemu bug

old qemu (before april 2020) have a bug in the layout of
struct ucontext, so we get invalid values under qemu-userspace emulation
when inspecting the signal context.  Try to recognize this and
graciously error out instead of segfaulting in the backtracer routines.
---
 tccrun.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tccrun.c b/tccrun.c
index 0609cb4c..17f1eebc 100644
--- a/tccrun.c
+++ b/tccrun.c
@@ -843,8 +843,10 @@ static int rt_get_caller_pc(addr_t *paddr, rt_context *rc, int level)
         *paddr = rc->ip;
     } else {
         addr_t *fp = (addr_t*)rc->fp;
-        while (--level)
+        while (--level && fp >= (addr_t*)0x1000)
             fp = (addr_t *)fp[-2];
+        if (fp < (addr_t*)0x1000)
+          return -1;
         *paddr = fp[-1];
     }
     return 0;