Bug 1572238 - Dump assertion stacks using __android_log_print. r=Ehsan

Defines an android-only version of nsTraceRefcnt::WalkTheStack that takes a function callback, which outputs the stack frame buffer to `__android_log_print`. Also uses `__wrap_dladdr` in MozDescribeCodeAddress, which outputs slightly more informative data for the stack trace (instead of instances of '???/??? [???]').

Differential Revision: https://phabricator.services.mozilla.com/D46868

--HG--
extra : moz-landing-system : lando

mfbt/Assertions.h

@@ -21,6 +21,8 @@
 #include "mozilla/Types.h"
 #ifdef MOZ_DUMP_ASSERTION_STACK
 #  include "nsTraceRefcnt.h"
+#  include "mozilla/StackWalk.h"
+#  include <algorithm>
 #endif
 
 /*
@@ -161,6 +163,21 @@ MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename,
   __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
                       "Assertion failure: %s, at %s:%d\n", aStr, aFilename,
                       aLine);
+#  if defined(MOZ_DUMP_ASSERTION_STACK)
+  nsTraceRefcnt::WalkTheStack(
+      [](uint32_t aFrameNumber, void* aPC, void* aSP, void* aClosure) {
+        MozCodeAddressDetails details;
+        static const size_t buflen = 1024;
+        char buf[buflen + 1];  // 1 for trailing '\n'
+
+        MozDescribeCodeAddress(aPC, &details);
+        MozFormatCodeAddressDetails(buf, buflen, aFrameNumber, aPC, &details);
+        size_t len = std::min(strlen(buf), buflen + 1 - 2);
+        buf[len++] = '\n';
+        buf[len] = '\0';
+        __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert", "%s", buf);
+      });
+#  endif
 #else
   fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
 #  if defined(MOZ_DUMP_ASSERTION_STACK)

mozglue/misc/StackWalk.cpp

@@ -14,6 +14,11 @@
 
 #include <string.h>
 
+#if defined(ANDROID) && defined(MOZ_LINKER)
+#  include "ElfLoader.h"
+#  include <android/log.h>
+#endif
+
 using namespace mozilla;
 
 // for _Unwind_Backtrace from libcxxrt or libunwind
@@ -799,7 +804,13 @@ bool MFBT_API MozDescribeCodeAddress(void* aPC,
   aDetails->foffset = 0;
 
   Dl_info info;
+
+#  if defined(ANDROID) && defined(MOZ_LINKER)
+  int ok = __wrap_dladdr(aPC, &info);
+#  else
   int ok = dladdr(aPC, &info);
+#  endif
+
   if (!ok) {
     return true;
   }

mozglue/misc/moz.build

@@ -82,6 +82,11 @@ else:
         'Mutex_posix.cpp',
     ]
 
+if CONFIG['MOZ_LINKER']:
+    LOCAL_INCLUDES += [
+        '/mozglue/linker',
+    ]
+
 SOURCES += [
     'decimal/Decimal.cpp',
 ]

xpcom/base/nsTraceRefcnt.cpp

@@ -762,6 +762,13 @@ void nsTraceRefcnt::WalkTheStack(FILE* aStream) {
   MozStackWalk(PrintStackFrame, /* skipFrames */ 2, /* maxFrames */ 0, aStream);
 }
 
+#ifdef ANDROID
+void nsTraceRefcnt::WalkTheStack(void (*aWriter)(uint32_t, void*, void*,
+                                                 void*)) {
+  MozStackWalk(aWriter, /* skipFrames */ 2, /* maxFrames */ 0, nullptr);
+}
+#endif
+
 /**
  * This is a variant of |WalkTheStack| that uses |CodeAddressService| to cache
  * the results of |NS_DescribeCodeAddress|. If |WalkTheStackCached| is being

xpcom/base/nsTraceRefcnt.h

@@ -18,6 +18,9 @@ class nsTraceRefcnt {
   static void ResetStatistics();
 
   static void WalkTheStack(FILE* aStream);
+#ifdef ANDROID
+  static void WalkTheStack(void (*aWriter)(uint32_t, void*, void*, void*));
+#endif
 
   /**
    * Tell nsTraceRefcnt whether refcounting, allocation, and destruction