[ASan] Support `{f}puts(NULL)` on Darwin

[yln]

Summary

On Darwin, the man page states that "both fputs() and puts() print
`(null)' if str is NULL."

rdar://48227136

[Lekensteyn]

LGTM. Not sure when this was added, but it must have been present since at least Mac OS X 10.7.3:
https://opensource.apple.com/source/Libc/Libc-763.12/stdio/fputs.3.auto.html
https://opensource.apple.com/source/Libc/Libc-763.12/stdio/FreeBSD/fputs.c.patch.auto.html

[delcypher]

compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc

1244

@yln

There are a few things I would have done differently here

• Add a comment explaining why we do this on mac. Just referencing the man page is probably fine.
• put COMMON_INTERCEPTOR_READ_RANGE(...) in curly braces. Because COMMON_INTERCEPTOR_READ_RANGE is a macro this feels like a disaster waiting to happen because the macro could expand into to multiple statements with the end result being that only the first statement gets guarded. I looked at how COMMON_INTERCEPTOR_READ_RANGE is implement and it's fine in this case because it uses (after several macro expansions) do {...} while (false) idiom.

[yln]

compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc

1244

Good points, thanks!
Updated in be7a7ae0c3da18138fa5f117765c56b5ee8df3c4.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc

 #define INIT_FGETS
 #endif
 
 #if SANITIZER_INTERCEPT_FPUTS
 INTERCEPTOR_WITH_SUFFIX(int, fputs, char *s, void *file) {
   // libc file streams can call user-supplied functions, see fopencookie.
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, fputs, s, file);
+  if (!SANITIZER_MAC || s)
     COMMON_INTERCEPTOR_READ_RANGE(ctx, s, REAL(strlen)(s) + 1);
   return REAL(fputs)(s, file);
 }
 #define INIT_FPUTS COMMON_INTERCEPT_FUNCTION(fputs)
 #else
 #define INIT_FPUTS
 #endif
 
 #if SANITIZER_INTERCEPT_PUTS
 INTERCEPTOR(int, puts, char *s) {
   // libc file streams can call user-supplied functions, see fopencookie.
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, puts, s);
+  if (!SANITIZER_MAC || s)
     COMMON_INTERCEPTOR_READ_RANGE(ctx, s, REAL(strlen)(s) + 1);
   return REAL(puts)(s);
 }
 #define INIT_PUTS COMMON_INTERCEPT_FUNCTION(puts)
 #else
 #define INIT_PUTS
 #endif
 
 #if SANITIZER_INTERCEPT_PRCTL

compiler-rt/trunk/test/sanitizer_common/TestCases/Darwin/fputs_puts_null.cc

+// On Darwin, the man page states that "both fputs() and puts() print `(null)'
+// if str is NULL."
+//
+// RUN: %clangxx -g %s -o %t && %run %t | FileCheck %s
+// CHECK: {{^\(null\)---\(null\)$}}
+
+#include <assert.h>
+#include <stdio.h>
+
+int main(void) {
+  assert(fputs(NULL, stdout) >= 0);
+  fputs("---", stdout);
+  assert(puts(NULL) >= 0);
+
+  return 0;
+}