thirdparty/patches/libunwind-Use-syscall-directly-in-write_validate-to-avoid-ASAN.patch

From 7d6cc6696ab8a808da3dbe23ca2493ddf2799b56 Mon Sep 17 00:00:00 2001
From: Dave Watson <davejwatson@fb.com>
Date: Wed, 17 Jan 2018 08:04:05 -0800
Subject: [PATCH 1/1] Use syscall directly in write_validate to avoid ASAN
 errors

ASAN will complain about this write call with the following error:

ERROR: AddressSanitizer: stack-buffer-underflow on address
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext

This is similar to what google's abseil does to work around the issue.

Reported-by: qiwang@fb.com
---
 src/x86_64/Ginit.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/x86_64/Ginit.c b/src/x86_64/Ginit.c
index 6281b76..2a84a1e 100644
--- a/src/x86_64/Ginit.c
+++ b/src/x86_64/Ginit.c
@@ -34,6 +34,7 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.  */
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 
 #include "unwind_i.h"
 
@@ -107,7 +108,8 @@ write_validate (void *addr)
 
   do
     {
-      ret = write (mem_validate_pipe[1], addr, 1);
+      /* use syscall insteadof write() so that ASAN does not complain */
+      ret = syscall (SYS_write, mem_validate_pipe[1], addr, 1);
     }
   while ( errno == EINTR );
 
-- 
2.7.4