3 files changed, 57 insertions, 0 deletions
diff --git a/browser/app/Makefile.in b/browser/app/Makefile.in
index d807b4337..cb35ed1fb 100644
--- a/browser/app/Makefile.in
+++ b/browser/app/Makefile.in
@@ -23,6 +23,14 @@ NSDISTMODE = copy
 
 include $(topsrcdir)/config/config.mk
 
+# If we are trying to show an error dialog about the lack of SSE2 support,
+# make sure that code itself doesn't use SSE2.
+ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+CXXFLAGS := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXXFLAGS))
+CXX := $(filter-out -march=% -msse2 -mfpmath=sse,$(CXX))
+CXXFLAGS += -mno-sse2 -mfpmath=387
+endif
+
 ifeq ($(OS_ARCH),WINNT)
 # Rebuild firefox.exe if the manifest changes - it's included by splash.rc.
 # (this dependency should really be just for firefox.exe, not other targets)
diff --git a/browser/app/moz.build b/browser/app/moz.build
index 1004e280c..9650761ee 100644
--- a/browser/app/moz.build
+++ b/browser/app/moz.build
@@ -70,6 +70,10 @@ if CONFIG['HAVE_CLOCK_MONOTONIC']:
 if CONFIG['MOZ_GPSD']:
     DEFINES['MOZ_GPSD'] = True
 
+
+if CONFIG['MOZ_LINUX_SSE2_STARTUP_ERROR']:
+    DEFINES['MOZ_LINUX_SSE2_STARTUP_ERROR'] = True
+
 for icon in ('firefox', 'document', 'newwindow', 'newtab', 'pbmode'):
     DEFINES[icon.upper() + '_ICO'] = '"%s/dist/branding/%s.ico"' % (
         TOPOBJDIR, icon)
diff --git a/browser/app/nsBrowserApp.cpp b/browser/app/nsBrowserApp.cpp
index 66ea8aed5..fc5ea8785 100644
--- a/browser/app/nsBrowserApp.cpp
+++ b/browser/app/nsBrowserApp.cpp
@@ -35,6 +35,51 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/WindowsDllBlocklist.h"
 
+#ifdef MOZ_LINUX_SSE2_STARTUP_ERROR
+#include <cpuid.h>
+#include "mozilla/Unused.h"
+
+static bool
+IsSSE2Available()
+{
+  // The rest of the app has been compiled to assume that SSE2 is present
+  // unconditionally, so we can't use the normal copy of SSE.cpp here.
+  // Since SSE.cpp caches the results and we need them only transiently,
+  // instead of #including SSE.cpp here, let's just inline the specific check
+  // that's needed.
+  unsigned int level = 1u;
+  unsigned int eax, ebx, ecx, edx;
+  unsigned int bits = (1u<<26);
+  unsigned int max = __get_cpuid_max(0, nullptr);
+  if (level > max) {
+    return false;
+  }
+  __cpuid_count(level, 0, eax, ebx, ecx, edx);
+  return (edx & bits) == bits;
+}
+
+static const char sSSE2Message[] =
+    "This browser version requires a processor with the SSE2 instruction "
+    "set extension.\n";
+
+__attribute__((constructor))
+static void
+SSE2Check()
+{
+  if (IsSSE2Available()) {
+    return;
+  }
+  // Using write() in order to avoid jemalloc-based buffering. Ignoring return
+  // values, since there isn't much we could do on failure and there is no
+  // point in trying to recover from errors.
+  MOZ_UNUSED(write(STDERR_FILENO,
+                   sSSE2Message,
+                   MOZ_ARRAY_LENGTH(sSSE2Message) - 1));
+  // _exit() instead of exit() to avoid running the usual "at exit" code.
+  _exit(255);
+}
+#endif
+
 #if !defined(MOZ_WIDGET_COCOA) && !defined(MOZ_WIDGET_ANDROID)
 #define MOZ_BROWSER_CAN_BE_CONTENTPROC
 #include "../../ipc/contentproc/plugin-container.cpp"