[compiler-rt | interceptors] Provide an intercept override knob.

[sivachandra]

Summary

This knob is useful for downstream users who want that some of their
libc functions to not be intercepted.

[eugenis]

@vitalybuka @kcc

compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h

605

SANITIZER_OVERRIDE_INTERCEPTORS?
The current name sounds like an interceptor for a function named override.

[sivachandra]

Change the macro name as suggested.

[sivachandra]

Changed the macro name as suggested.

[eugenis]

LGTM

[thakis]

Out of interest, how do you run tests after disabling interception of a function with this? Won't the test for that function fail then?

[thakis]

In D97740#3549963, @thakis wrote:

Out of interest, how do you run tests after disabling interception of a function with this? Won't the test for that function fail then?

To answer my own question: One option is to use something like e.g. LIT_FILTER_OUT='^SanitizerCommon-(a|l|m|ub|t)san-x86_64-Linux :: (Linux/crypt_r.cpp|Posix/crypt.cpp)$' ninja check-sanitizer.

compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h

 #define SANITIZER_INTERCEPT_QSORT_R SI_GLIBC
 // sigaltstack on i386 macOS cannot be intercepted due to setjmp()
 // calling it and assuming that it does not clobber registers.
 #define SANITIZER_INTERCEPT_SIGALTSTACK \
   (SI_POSIX && !(SANITIZER_MAC && SANITIZER_I386))
 #define SANITIZER_INTERCEPT_UNAME (SI_POSIX && !SI_FREEBSD)
 #define SANITIZER_INTERCEPT___XUNAME SI_FREEBSD
 
+// This macro gives a way for downstream users to override the above
+// interceptor macros irrespective of the platform they are on. They have
+// to do two things:
+// 1. Build compiler-rt with -DSANITIZER_OVERRIDE_INTERCEPTORS.
+// 2. Provide a header file named sanitizer_intercept_overriders.h in the
+//    include path for their compiler-rt build.
+// An example of an overrider for strlen interceptor that one can list in
+// sanitizer_intercept_overriders.h is as follows:
+//
+// #ifdef SANITIZER_INTERCEPT_STRLEN
+// #undef SANITIZER_INTERCEPT_STRLEN
+// #define SANITIZER_INTERCEPT_STRLEN <value of choice>
+// #endif
+//
+// This "feature" is useful for downstream users who do not want some of
+// their libc funtions to be intercepted. They can selectively disable
+// interception of those functions.
+#ifdef SANITIZER_OVERRIDE_INTERCEPTORS
+#include <sanitizer_intercept_overriders.h>
+#endif
+
 #endif  // #ifndef SANITIZER_PLATFORM_INTERCEPTORS_H