From bf6e7848a0e26fa855ce8330dfda04dd4aca83bd Mon Sep 17 00:00:00 2001
From: Kuba Brecka <kuba.brecka@gmail.com>
Date: Mon, 31 Oct 2016 18:52:32 +0000
Subject: [PATCH] [asan] Move instrumented null-terminated strings to a special
 section, compiler-rt part

On Darwin, simple C null-terminated constant strings normally end up in the __TEXT,__cstring section of the resulting Mach-O binary. When instrumented with ASan, these strings are transformed in a way that they cannot be in __cstring (the linker unifies the content of this section and strips extra NUL bytes, which would break instrumentation), and are put into a generic __const section. This breaks some of the tools that we have: Some tools need to scan all C null-terminated strings in Mach-O binaries, and scanning all the contents of __const has a large performance penalty. This patch instead introduces a special section, __asan_cstring which will now hold the instrumented null-terminated strings.

Differential Revision: https://reviews.llvm.org/D25026

llvm-svn: 285620
---
 .../asan/TestCases/Darwin/cstring_section.c     | 17 +++++++++++++++++
 .../test/asan/TestCases/Darwin/odr-lto.cc       |  8 ++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 compiler-rt/test/asan/TestCases/Darwin/cstring_section.c

diff --git a/compiler-rt/test/asan/TestCases/Darwin/cstring_section.c b/compiler-rt/test/asan/TestCases/Darwin/cstring_section.c
new file mode 100644
index 000000000000..952d6fcdd465
--- /dev/null
+++ b/compiler-rt/test/asan/TestCases/Darwin/cstring_section.c
@@ -0,0 +1,17 @@
+// Test that AddressSanitizer moves constant strings into a separate section.
+
+// RUN: %clang_asan -c -o %t %s
+// RUN: llvm-objdump -s %t | FileCheck %s
+
+// Check that "Hello.\n" is in __asan_cstring and not in __cstring.
+// CHECK: Contents of section __asan_cstring:
+// CHECK: 48656c6c {{.*}} Hello.
+// CHECK: Contents of section __const:
+// CHECK-NOT: 48656c6c {{.*}} Hello.
+// CHECK: Contents of section __cstring:
+// CHECK-NOT: 48656c6c {{.*}} Hello.
+
+int main(int argc, char *argv[]) {
+  argv[0] = "Hello.\n";
+  return 0;
+}
diff --git a/compiler-rt/test/asan/TestCases/Darwin/odr-lto.cc b/compiler-rt/test/asan/TestCases/Darwin/odr-lto.cc
index 23f1e05c3e1e..40abec5827d5 100644
--- a/compiler-rt/test/asan/TestCases/Darwin/odr-lto.cc
+++ b/compiler-rt/test/asan/TestCases/Darwin/odr-lto.cc
@@ -19,9 +19,11 @@ void putstest();
 
 #if PART == 1
 
+static const char *my_global = "test\n\00abc";
+
 int main()
 {
-  fputs("test\n", stderr);
+  fputs(my_global, stderr);
   putstest();
   fprintf(stderr, "Done.\n");
   return 0;
@@ -29,9 +31,11 @@ int main()
 
 #else // PART == 1
 
+static const char *my_other_global = "test\n\00abc";
+
 void putstest()
 {
-  fputs("test\n", stderr);
+  fputs(my_other_global, stderr);
 }
 
 #endif // PART == 1