From 2c431cb961f739d8325002e7c87798e00cc1eef9 Mon Sep 17 00:00:00 2001
From: Ted Mielczarek <ted@mielczarek.org>
Date: Mon, 27 Mar 2017 14:40:22 -0400
Subject: [PATCH] bug 1275780 - capture Rust panic message in crash reports.
 r=froydnj

MozReview-Commit-ID: IUlYqPEtkgg

--HG--
extra : rebase_source : c328db9b979eb2ff1f469b6ebc4a63e7ac337c63
---
 toolkit/crashreporter/nsExceptionHandler.cpp  | 21 ++++++++-
 .../test/unit/test_crash_rust_panic.js        |  2 +-
 toolkit/library/rust/shared/lib.rs            | 47 +++++++++++++++++++
 3 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/toolkit/crashreporter/nsExceptionHandler.cpp b/toolkit/crashreporter/nsExceptionHandler.cpp
index f7ccda818481..78a20aa54c3d 100644
--- a/toolkit/crashreporter/nsExceptionHandler.cpp
+++ b/toolkit/crashreporter/nsExceptionHandler.cpp
@@ -116,6 +116,13 @@ using google_breakpad::PageAllocator;
 using namespace mozilla;
 using mozilla::ipc::CrashReporterClient;
 
+// From toolkit/library/rust/shared/lib.rs
+extern "C" {
+  void install_rust_panic_hook();
+  bool get_rust_panic_reason(char** reason, size_t* length);
+}
+
+
 namespace CrashReporter {
 
 #ifdef XP_WIN32
@@ -1131,7 +1138,17 @@ bool MinidumpCallback(
     WriteGlobalMemoryStatus(&apiData, &eventFile);
 #endif // XP_WIN
 
-    if (gMozCrashReason) {
+    char* rust_panic_reason;
+    size_t rust_panic_len;
+    if (get_rust_panic_reason(&rust_panic_reason, &rust_panic_len)) {
+      // rust_panic_reason is not null-terminated.
+      WriteLiteral(apiData, "MozCrashReason=");
+      apiData.WriteBuffer(rust_panic_reason, rust_panic_len);
+      WriteLiteral(apiData, "\n");
+      WriteLiteral(eventFile, "MozCrashReason=");
+      eventFile.WriteBuffer(rust_panic_reason, rust_panic_len);
+      WriteLiteral(eventFile, "\n");
+    } else if (gMozCrashReason) {
       WriteAnnotation(apiData, "MozCrashReason", gMozCrashReason);
       WriteAnnotation(eventFile, "MozCrashReason", gMozCrashReason);
     }
@@ -1577,6 +1594,8 @@ nsresult SetExceptionHandler(nsIFile* aXREDirectory,
   if (gExceptionHandler)
     return NS_ERROR_ALREADY_INITIALIZED;
 
+  install_rust_panic_hook();
+
 #if !defined(DEBUG) || defined(MOZ_WIDGET_GONK)
   // In non-debug builds, enable the crash reporter by default, and allow
   // disabling it with the MOZ_CRASHREPORTER_DISABLE environment variable.
diff --git a/toolkit/crashreporter/test/unit/test_crash_rust_panic.js b/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
index c8691c74c2b0..68c50a8b5365 100644
--- a/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
+++ b/toolkit/crashreporter/test/unit/test_crash_rust_panic.js
@@ -4,7 +4,7 @@ function run_test() {
              Components.classes["@mozilla.org/xpcom/debug;1"].getService(Components.interfaces.nsIDebug2).rustPanic("OH NO");
            },
            function(mdump, extra) {
-             //TODO: check some extra things?
+             do_check_eq(extra.MozCrashReason, "OH NO");
            },
           // process will exit with a zero exit status
           true);
diff --git a/toolkit/library/rust/shared/lib.rs b/toolkit/library/rust/shared/lib.rs
index f0c1a487ecce..936fd1875511 100644
--- a/toolkit/library/rust/shared/lib.rs
+++ b/toolkit/library/rust/shared/lib.rs
@@ -11,11 +11,58 @@ extern crate rust_url_capi;
 #[cfg(feature = "quantum_render")]
 extern crate webrender_bindings;
 
+use std::boxed::Box;
 use std::ffi::CStr;
 use std::os::raw::c_char;
+use std::panic;
 
 /// Used to implement `nsIDebug2::RustPanic` for testing purposes.
 #[no_mangle]
 pub extern "C" fn intentional_panic(message: *const c_char) {
     panic!("{}", unsafe { CStr::from_ptr(message) }.to_string_lossy());
 }
+
+/// Contains the panic message, if set.
+static mut PANIC_REASON: Option<(*const str, usize)> = None;
+
+/// Configure a panic hook to capture panic messages for crash reports.
+///
+/// We don't store this in `gMozCrashReason` because:
+/// a) Rust strings aren't null-terminated, so we'd have to allocate
+///    memory to get a null-terminated string
+/// b) The panic=abort handler is going to call `abort()` on non-Windows,
+///    which is `mozalloc_abort` for us, which will use `MOZ_CRASH` and
+///    overwrite `gMozCrashReason` with an unhelpful string.
+#[no_mangle]
+pub extern "C" fn install_rust_panic_hook() {
+    panic::set_hook(Box::new(|info| {
+        // Try to handle &str/String payloads, which should handle 99% of cases.
+        let payload = info.payload();
+        // We'll hold a raw *const str here, but it will be OK because
+        // Rust is going to abort the process before the payload could be
+        // deallocated.
+        if let Some(s) = payload.downcast_ref::<&str>() {
+            unsafe { PANIC_REASON = Some((*s as *const str, s.len())) }
+        } else if let Some(s) = payload.downcast_ref::<String>() {
+            unsafe { PANIC_REASON = Some((s.as_str() as *const str, s.len())) }
+        } else {
+            // Not the most helpful thing, but seems unlikely to happen
+            // in practice.
+            println!("Unhandled panic payload!");
+        }
+    }));
+}
+
+#[no_mangle]
+pub extern "C" fn get_rust_panic_reason(reason: *mut *const c_char, length: *mut usize) -> bool {
+    unsafe {
+        match PANIC_REASON {
+            Some((s, len)) => {
+                *reason = s as *const c_char;
+                *length = len;
+                true
+            }
+            None => false,
+        }
+    }
+}