Fix gdbserver-xen support on older kernels.

The xc_ptrace API relies on errno for passing success/failure
indication back to callers.  However, mapping operations that fall
back on legacy APIs may leave errno set to a non-zero result even
thought the operation is successful.  This patch resets errno after
successful map operations so that xc_ptrace doesn't inadvertently
return a failure.

Signed-off-by: Justin Gibbs <gibbs@scsiguy.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/tools/libxc/xc_ptrace.c b/tools/libxc/xc_ptrace.c
index 725a022339..e91ac56da6 100644
--- a/tools/libxc/xc_ptrace.c
+++ b/tools/libxc/xc_ptrace.c
@@ -193,6 +193,13 @@ map_domain_va(
     if (map == NULL)
         return NULL;
 
+    /*
+     * Due to the use of API fallback code in libxc, errno may
+     * be clobberred during successful operations.  Since the caller
+     * of xc_ptrace is depending on errno for return status, clear
+     * errno here.
+     */
+    errno = 0;
     return map + (va & ~PAGE_MASK);
 }