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/* -*- Mode: C++; tab-width: 40; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "nsX11ErrorHandler.h"
#include "prenv.h"
#include "nsXULAppAPI.h"
#include "nsExceptionHandler.h"
#include "nsDebug.h"
#include "nsString.h"
#include "nsTArray.h"
#include "mozilla/X11Util.h"
#include <X11/Xlib.h>
#define BUFSIZE 2048 // What Xlib uses with XGetErrorDatabaseText
struct XExtension {
nsCString name;
int major_opcode;
XExtension(const char* aName, int aCode) : name(aName), major_opcode(aCode) {}
static nsTArray<XExtension> sXExtensions;
// man XSetErrorHandler says "the error handler should not call any
// functions (directly or indirectly) on the display that will generate
// protocol requests or that will look for input events" so we query the
// extension list early to avoid problems.
static void QueryXExtensions(Display* aDisplay) {
if (!sXExtensions.IsEmpty() || !aDisplay) {
int nExts = 0;
char** extNames = XListExtensions(aDisplay, &nExts);
if (!extNames) {
for (int i = 0; i < nExts; ++i) {
int major_opcode, first_event, first_error;
if (XQueryExtension(aDisplay, extNames[i], &major_opcode, &first_event,
&first_error)) {
sXExtensions.EmplaceBack(extNames[i], major_opcode);
extern "C" {
int X11Error(Display* display, XErrorEvent* event) {
#ifdef DEBUG
// Get an indication of how long ago the request that caused the error was
// made.
unsigned long age = NextRequest(display) - event->serial;
// Get a string to represent the request that caused the error.
nsAutoCString message;
if (event->request_code < 128) {
// Core protocol request
} else {
// Extension request
for (XExtension& ext : sXExtensions) {
if (ext.major_opcode == event->request_code) {
char buffer[BUFSIZE];
if (message.IsEmpty()) {
buffer[0] = '\0';
} else {
XGetErrorDatabaseText(display, "XRequest", message.get(), "", buffer,
nsAutoCString notes;
if (buffer[0]) {
} else {
notes.AppendLiteral("Request ");
notes.AppendLiteral(": ");
// Get a string to describe the error.
XGetErrorText(display, event->error_code, buffer, sizeof(buffer));
#ifdef DEBUG
// For requests where Xlib gets the reply synchronously, |age| will be 1
// and the stack will include the function making the request. For
// asynchronous requests, the current stack will often be unrelated to the
// point of making the request, even if |age| is 1, but sometimes this may
// help us count back to the point of the request. With XSynchronize on,
// the stack will include the function making the request, even though
// |age| will be 2 for asynchronous requests because XSynchronize is
// implemented by an empty request from an XSync, which has not yet been
// processed.
if (age > 1) {
// XSynchronize returns the previous "after function". If a second
// XSynchronize call returns the same function after an enable call then
// synchronization must have already been enabled.
if (XSynchronize(display, X11True) == XSynchronize(display, X11False)) {
notes.AppendLiteral("; sync");
} else {
notes.AppendLiteral("; ");
notes.AppendLiteral(" requests ago");
// The resource id is unlikely to be useful in a crash report without
// context of other ids, but add it to the debug console output.
notes.AppendLiteral("; id=0x");
notes.AppendInt(uint32_t(event->resourceid), 16);
# ifdef MOZ_X11
// Actually, for requests where Xlib gets the reply synchronously,
// MOZ_X_SYNC=1 will not be necessary, but we don't have a table to tell us
// which requests get a synchronous reply.
if (!PR_GetEnv("MOZ_X_SYNC")) {
"\nRe-running with MOZ_X_SYNC=1 in the environment may give a more "
"helpful backtrace.");
# endif
return 0;
void InstallX11ErrorHandler() {
if (Display* display = mozilla::DefaultXDisplay()) {
if (PR_GetEnv("MOZ_X_SYNC")) {
XSynchronize(display, X11True);
void CleanupX11ErrorHandler() { sXExtensions.Clear(); }