[PATCH] D82691: Disable interception of sigaltstack on i386 macOS.

[Dan Liew via Phabricator via llvm-commits]

delcypher created this revision.
delcypher added reviewers: kubamracek, yln, eugenis.
Herald added subscribers: Sanitizers, kristof.beyls.
Herald added a project: Sanitizers.

28c91219c7e <https://reviews.llvm.org/rG28c91219c7e2180c3605ce403c05c4eccac6f615> 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 caller-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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82691

Files:
  compiler-rt/lib/sanitizer_common/sanitizer_platform.h
  compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h


Index: compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
@@ -596,7 +596,10 @@
 #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
 
Index: compiler-rt/lib/sanitizer_common/sanitizer_platform.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_platform.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_platform.h
@@ -132,6 +132,12 @@
 # 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)


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