Disable interception of sigaltstack on i386 macOS.

[delcypher]

Summary

28c91219c7e introduced an interceptor for sigaltstack. It turns out this
broke setjmp on i386 macOS. This is because the implementation of setjmp on
i386 macOS is written in assembly and makes the assumption that the call to
sigaltstack does not clobber any registers. Presumably that assumption was
made because it's a system call. In particular setjmp assumes that before
and after the call that %ecx will contain a pointer the jmp_buf. The
current interceptor breaks this assumption because it's written in C++ and
%ecx is not a calle-saved register. This could be fixed by writing a
trampoline interceptor to the existing interceptor in assembly that
ensures all the registers are preserved. However, this is a lot of work
for very little gain. Instead this patch just disables the interceptor
on i386 macOS.

For other Darwin architectures it currently appears to be safe to intercept
sigaltstack using the current implementation because:

• setjmp for x86_64 saves the pointer jmp_buf to the stack before calling sigaltstack.
• setjmp for armv7/arm64/arm64_32/arm64e appears to not call sigaltstack at all.

This patch should unbreak (once they are re-enabled) the following
tests:

AddressSanitizer-Unit :: ./Asan-i386-calls-Test/AddressSanitizer.LongJmpTest
AddressSanitizer-Unit :: ./Asan-i386-calls-Test/AddressSanitizer.SigLongJmpTest
AddressSanitizer-Unit :: ./Asan-i386-inline-Test/AddressSanitizer.LongJmpTest
AddressSanitizer-Unit :: ./Asan-i386-inline-Test/AddressSanitizer.SigLongJmpTest
AddressSanitizer-i386-darwin :: TestCases/longjmp.cpp

This patch introduces a SANITIZER_I386 macro for convenience.

rdar://problem/62141412

[yln]

Thanks!

compiler-rt/lib/sanitizer_common/sanitizer_platform.h

 #endif
 
 #if defined(__x86_64__) && !defined(_LP64)
 # define SANITIZER_X32 1
 #else
 # define SANITIZER_X32 0
 #endif
 
+#if defined(__i386__) || defined(_M_IX86)
+# define SANITIZER_I386 1
+#else
+# define SANITIZER_I386 0
+#endif
+
 #if defined(__mips__)
 # define SANITIZER_MIPS 1
 # if defined(__mips64)
 #  define SANITIZER_MIPS32 0
 #  define SANITIZER_MIPS64 1
 # else
 #  define SANITIZER_MIPS32 1
 #  define SANITIZER_MIPS64 0

compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h

#define SANITIZER_INTERCEPT_GETRANDOM \
   ((SI_LINUX && __GLIBC_PREREQ(2, 25)) || SI_FREEBSD)
 #define SANITIZER_INTERCEPT___CXA_ATEXIT SI_NETBSD
 #define SANITIZER_INTERCEPT_ATEXIT SI_NETBSD
 #define SANITIZER_INTERCEPT_PTHREAD_ATFORK SI_NETBSD
 #define SANITIZER_INTERCEPT_GETENTROPY SI_FREEBSD
 #define SANITIZER_INTERCEPT_QSORT \
   (SI_POSIX && !SI_IOSSIM && !SI_WATCHOS && !SI_TVOS && !SI_ANDROID)
 #define SANITIZER_INTERCEPT_QSORT_R (SI_LINUX && !SI_ANDROID)
-#define SANITIZER_INTERCEPT_SIGALTSTACK SI_POSIX
+// 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
 
 #endif  // #ifndef SANITIZER_PLATFORM_INTERCEPTORS_H