Bug 1514965 - Part 2: Enable clang -ftrivial-auto-var-init to initialize local variables with 0xAA in debug builds. r=froydnj

Disable -ftrivial-auto-var-init for DllBLocklistWin.cpp with clang-cl because the file's interceptions happen so early in the main process that the loader hasn't yet resolved the import of memset (used by -ftrivial-auto-var-init) from vcruntime140.dll.

Disable -ftrivial-auto-var-init on Linux32 because it causes some xpcshell test failures.

Differential Revision: https://phabricator.services.mozilla.com/D42273

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

browser/app/winlauncher/moz.build

@@ -32,6 +32,19 @@ if CONFIG['CC_TYPE'] == 'clang-cl':
 else:
     SOURCES['DllBlocklistWin.cpp'].flags += ['-ffreestanding']
 
+# Disable -ftrivial-auto-var-init=pattern for DllBlocklistWin.cpp because
+# the file's interceptions happen so early in the main process that the
+# loader hasn't yet resolved the import of memset (used by
+# -ftrivial-auto-var-init) from vcruntime140.dll.
+if CONFIG['CC_TYPE'] == 'clang-cl':
+    SOURCES['DllBlocklistWin.cpp'].flags += [
+        '-Xclang', '-ftrivial-auto-var-init=uninitialized',
+    ]
+else:
+    SOURCES['DllBlocklistWin.cpp'].flags += [
+        '-ftrivial-auto-var-init=uninitialized',
+    ]
+
 OS_LIBS += [
     'ntdll',
     'oleaut32',

build/moz.configure/toolchain.configure

@@ -1545,8 +1545,9 @@ option('--enable-hardening', env='MOZ_SECURITY_HARDENING',
 # possible security flags will be omitted by --disable-hardening, as many are
 # compiler-default options we do not explicitly enable.)
 @depends('--enable-hardening', '--enable-address-sanitizer',
-         '--enable-optimize', c_compiler, target)
-def security_hardening_cflags(hardening_flag, asan, optimize, c_compiler, target):
+         '--enable-debug', '--enable-optimize', c_compiler, target)
+def security_hardening_cflags(hardening_flag, asan, debug, optimize, c_compiler,
+                              target):
     compiler_is_gccish = c_compiler.type in ('gcc', 'clang')
 
     flags = []
@@ -1580,6 +1581,18 @@ def security_hardening_cflags(hardening_flag, asan, optimize, c_compiler, target
                 js_flags.append("-fstack-protector-strong")
                 js_ldflags.append("-fstack-protector-strong")
 
+        # ftrivial-auto-var-init ------------------------------
+        # Initialize local variables with a 0xAA pattern in clang debug builds.
+        # Linux32 fails some xpcshell tests with -ftrivial-auto-var-init
+        linux32 = target.kernel == 'Linux' and target.cpu == 'x86'
+        if (c_compiler.type == 'clang' or c_compiler.type == 'clang-cl') and \
+            c_compiler.version >= '8' and debug and not linux32:
+            if c_compiler.type == 'clang-cl':
+                flags.append('-Xclang')
+                js_flags.append('-Xclang')
+            flags.append('-ftrivial-auto-var-init=pattern')
+            js_flags.append('-ftrivial-auto-var-init=pattern')
+
         # ASLR ------------------------------------------------
         # ASLR (dynamicbase) is enabled by default in clang-cl; but the
         # mingw-clang build requires it to be explicitly enabled