Merge pull request #2797 from kumpera/android_krait_bug

[android] Fix Krait CPU bug on Android.

diff --git a/mono/utils/mono-signal-handler.h b/mono/utils/mono-signal-handler.h
index fbe798eeb0e6321667023429bfc88b4cb65bb1ce..94335964cd08a58b4c50f791f171ef2b1ffe50fd 100644 (file)
--- a/mono/utils/mono-signal-handler.h
+++ b/mono/utils/mono-signal-handler.h
@@ -9,10 +9,53 @@
 
 #include "config.h"
 
-#ifdef ENABLE_EXTENSION_MODULE
-#include "../../../mono-extensions/mono/utils/mono-signal-handler.h"
+/*
+ * When a signal is delivered to a thread on a Krait Android device
+ * that's in the middle of skipping over an "IT" block, such as this
+ * one:
+ *
+ * 0x40184ef0 <dlfree+1308>:   ldr     r1, [r3, #0]
+ * 0x40184ef2 <dlfree+1310>:   add.w   r5, r12, r2, lsl #3
+ * 0x40184ef6 <dlfree+1314>:   lsls.w  r2, r0, r2
+ * 0x40184efa <dlfree+1318>:   tst     r2, r1
+ * ### this is the IT instruction
+ * 0x40184efc <dlfree+1320>:   itt     eq
+ * 0x40184efe <dlfree+1322>:   orreq   r2, r1
+ * ### signal arrives here
+ * 0x40184f00 <dlfree+1324>:   streq   r2, [r3, #0]
+ * 0x40184f02 <dlfree+1326>:   beq.n   0x40184f1a <dlfree+1350>
+ * 0x40184f04 <dlfree+1328>:   ldr     r2, [r5, #8]
+ * 0x40184f06 <dlfree+1330>:   ldr     r3, [r3, #16]
+ *
+ * then the first few (at most four, one would assume) instructions of
+ * the signal handler (!) might be skipped.  They happen to be the
+ * push of the frame pointer and return address, so once the signal
+ * handler has done its work, it returns into a SIGSEGV.
+ */
+
+#if defined (TARGET_ARM) && defined (HAVE_ARMV7) && defined (TARGET_ANDROID)
+#define KRAIT_IT_BUG_WORKAROUND        1
+#endif
+
+#ifdef KRAIT_IT_BUG_WORKAROUND
+#define MONO_SIGNAL_HANDLER_FUNC(access, name, arglist)                \
+       static void __krait_ ## name arglist;   \
+       __attribute__ ((naked)) access void                             \
+       name arglist                                                    \
+       {                                                               \
+               asm volatile (                                          \
+                             "mov r0, r0\n\t"                          \
+                             "mov r0, r0\n\t"                          \
+                             "mov r0, r0\n\t"                          \
+                             "mov r0, r0\n\t");                        \
+               asm volatile (                                          \
+                             "bx %0"                                   \
+                             : : "r" (__krait_ ## name));              \
+       }       \
+       static void __krait_ ## name arglist
 #endif
 
+
 /* Don't use this */
 #ifndef MONO_SIGNAL_HANDLER_FUNC
 #define MONO_SIGNAL_HANDLER_FUNC(access, name, arglist) access void name arglist