Changed WTFCrash to not trash the crash site register state.

https://bugs.webkit.org/show_bug.cgi?id=153996

Reviewed by Geoffrey Garen.

When doing post-mortem crash site analysis using data from crash reports, it is
immensely valuable to be able to infer the crashing program's state from the
register values at crash time.  However, for RELEASE_ASSERT failures, we crash
using WTFCrash(), and WTFCrash() is currently implemented as a function call
that, in turn, calls a lot of other functions to do crash handling before
actually crashing.  As a result, the register values captured in the crash
reports are not likely to still contain the values used by the caller function
that failed the RELEASE_ASSERT.

This patch aims to remedy this issue for non-debug builds on OS(DARWIN) ports.
It does so by changing WTFCrash() into an inlined function that has an inlined
asm statement to issues the CPU specific breakpoint trap instruction.  As a
result, for non-debug OS(DARWIN) builds, crashes due to failed RELEASE_ASSERTs
will now show up in crash reports as crashing due to EXC_BREAKPOINT (SIGTRAP)
instead of a EXC_BAD_ACCESS (SIGSEGV) on address 0xbbadbeef.

For debug and non-DARWIN builds, WTFCrash() behavior currently remains unchanged.

* wtf/Assertions.cpp:
* wtf/Assertions.h:



Canonical link: https://commits.webkit.org/172198@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@196397 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WTF/ChangeLog

@@ -1,3 +1,31 @@
+2016-02-09  Mark Lam  <mark.lam@apple.com>
+
+        Changed WTFCrash to not trash the crash site register state.
+        https://bugs.webkit.org/show_bug.cgi?id=153996
+
+        Reviewed by Geoffrey Garen.
+
+        When doing post-mortem crash site analysis using data from crash reports, it is
+        immensely valuable to be able to infer the crashing program's state from the
+        register values at crash time.  However, for RELEASE_ASSERT failures, we crash
+        using WTFCrash(), and WTFCrash() is currently implemented as a function call
+        that, in turn, calls a lot of other functions to do crash handling before
+        actually crashing.  As a result, the register values captured in the crash
+        reports are not likely to still contain the values used by the caller function
+        that failed the RELEASE_ASSERT.
+
+        This patch aims to remedy this issue for non-debug builds on OS(DARWIN) ports.
+        It does so by changing WTFCrash() into an inlined function that has an inlined
+        asm statement to issues the CPU specific breakpoint trap instruction.  As a
+        result, for non-debug OS(DARWIN) builds, crashes due to failed RELEASE_ASSERTs
+        will now show up in crash reports as crashing due to EXC_BREAKPOINT (SIGTRAP)
+        instead of a EXC_BAD_ACCESS (SIGSEGV) on address 0xbbadbeef.
+
+        For debug and non-DARWIN builds, WTFCrash() behavior currently remains unchanged.
+
+        * wtf/Assertions.cpp:
+        * wtf/Assertions.h:
+
 2016-02-09  Csaba Osztrogonác  <ossy@webkit.org>
 
         [GTK][EFL] Fix several build configuration related to SamplingProfiler after r196245

Source/WTF/wtf/Assertions.cpp

@@ -312,6 +312,7 @@ void WTFSetCrashHook(WTFCrashHookFunction function)
     globalHook = function;
 }
 
+#if !defined(NDEBUG) || !OS(DARWIN)
 void WTFCrash()
 {
     if (globalHook)
@@ -326,6 +327,7 @@ void WTFCrash()
     ((void(*)())0)();
 #endif
 }
+#endif // !defined(NDEBUG) || !OS(DARWIN)
 
 void WTFCrashWithSecurityImplication()
 {

Source/WTF/wtf/Assertions.h

@@ -162,7 +162,27 @@ WTF_EXPORT_PRIVATE bool WTFIsDebuggerAttached();
 #ifdef __cplusplus
 extern "C" {
 #endif
-    WTF_EXPORT_PRIVATE NO_RETURN_DUE_TO_CRASH void WTFCrash();
+#if defined(NDEBUG) && OS(DARWIN)
+ALWAYS_INLINE NO_RETURN_DUE_TO_CRASH void WTFCrash()
+{
+    // Crash with a SIGTRAP i.e EXC_BREAKPOINT.
+    // We are not using __builtin_trap because it is only guaranteed to abort, but not necessarily
+    // trigger a SIGTRAP. Instead, we use inline asm to ensure that we trigger the SIGTRAP.
+#if CPU(X86_64) || CPU(X86)
+    asm volatile ("int3");
+#elif CPU(ARM_THUMB2)
+    asm volatile ("bkpt #0");
+#elif CPU(ARM64)
+    asm volatile ("brk #0");
+#else
+#error "Unsupported CPU".
+#endif
+    __builtin_unreachable();
+}
+#else
+WTF_EXPORT_PRIVATE NO_RETURN_DUE_TO_CRASH void WTFCrash();
+#endif
+
 #ifdef __cplusplus
 }
 #endif