[Qemu-devel] [PATCH 2/9] linux-user: Add is_write segfault check for ARM hosts

[Alexander Graf <agraf@suse.de>]

When we get a segmentation fault we check whether the fault was a write. If
it was a write, it might be a fault because we tried to modify a code region.

This logic does not work on ARM hosts, because they don't evaluate whether a
segementation fault is due to a write. Instead they always declare it a read.

So self modifying code fails with a segmentation fault whenever it tries to
modify itself.

Add the is_write evaluation based on what the kernel tells us as fault reason.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 user-exec.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/user-exec.c b/user-exec.c
index 718c54f..bbeb0dd 100644
--- a/user-exec.c
+++ b/user-exec.c
@@ -448,8 +448,7 @@ int cpu_signal_handler(int host_signum, void *pinfo,
 #else
     pc = uc->uc_mcontext.arm_pc;
 #endif
-    /* XXX: compute is_write */
-    is_write = 0;
+    is_write = (uc->uc_mcontext.error_code & 0x800) ? 1 : 0;
     return handle_cpu_signal(pc, (unsigned long)info->si_addr,
                              is_write,
                              &uc->uc_sigmask, puc);
-- 
1.6.0.2