diff --git a/sdk_container/src/third_party/portage-stable/eclass/toolchain.eclass b/sdk_container/src/third_party/portage-stable/eclass/toolchain.eclass
index c7c366a37a..ac236f3127 100644
--- a/sdk_container/src/third_party/portage-stable/eclass/toolchain.eclass
+++ b/sdk_container/src/third_party/portage-stable/eclass/toolchain.eclass
@@ -1214,7 +1214,14 @@ toolchain_src_configure() {
 			# - https://git.musl-libc.org/cgit/musl/tree/INSTALL
 			# - bug #704784
 			# - https://gcc.gnu.org/PR93157
-			[[ ${CTARGET} == powerpc64-*-musl ]] && confgcc+=( --with-abi=elfv2 )
+			# musl additionally does not support libquadmath.  See:
+			# - https://gcc.gnu.org/PR116007
+			[[ ${CTARGET} == powerpc64-*-musl ]] && confgcc+=(
+				--with-abi=elfv2
+				--disable-libquadmath
+				--disable-libquadmath-support
+				--with-long-double-128=no
+			)
 
 			if in_iuse ieee-long-double; then
 				# musl requires 64-bit long double, not IBM double-double or IEEE quad.
@@ -1654,9 +1661,6 @@ gcc_do_filter_flags() {
 
 		# New in GCC 14.
 		filter-flags -Walloc-size
-	else
-		# Makes things painfully slow and no real benefit for the compiler.
-		append-flags $(test-flags-CC -fno-harden-control-flow-redundancy)
 	fi
 
 	# Please use USE=lto instead (bug #906007).
@@ -1894,7 +1898,6 @@ gcc_do_make() {
 #---->> src_test <<----
 
 # TODO: add JIT testing
-# TODO: add multilib testing
 toolchain_src_test() {
 	# GCC's testsuite is a special case.
 	#
@@ -1917,11 +1920,79 @@ toolchain_src_test() {
 	local -x LD_PRELOAD=
 
 	# Controls running expensive tests in e.g. the torture testsuite.
+	# Note that 'TEST', not 'TESTS', is correct here as it's a GCC
+	# testsuite variable, not ours.
 	local -x GCC_TEST_RUN_EXPENSIVE=1
 
-	# nonfatal here as we die if the comparison below fails. Also, note that
-	# the exit code of targets other than 'check' may be unreliable.
-	nonfatal emake -C "${WORKDIR}"/build -k "${GCC_TESTS_CHECK_TARGET}" RUNTESTFLAGS="${GCC_TESTS_RUNTESTFLAGS}"
+	# Use a subshell to allow meddling with flags just for the testsuite
+	(
+		# Workaround our -Wformat-security default which breaks
+		# various tests as it adds unexpected warning output.
+		GCC_TESTS_CFLAGS+=" -Wno-format-security -Wno-format"
+		GCC_TESTS_CXXFLAGS+=" -Wno-format-security -Wno-format"
+
+		# Workaround our -Wtrampolines default which breaks
+		# tests too.
+		GCC_TESTS_CFLAGS+=" -Wno-trampolines"
+		GCC_TESTS_CXXFLAGS+=" -Wno-trampolines"
+		# A handful of Ada (and objc++?) tests need an executable stack
+		GCC_TESTS_LDFLAGS+=" -Wl,--no-warn-execstack"
+		# Avoid confusing tests like Fortran/C interop ones where
+		# CFLAGS are used.
+		GCC_TESTS_CFLAGS+=" -Wno-complain-wrong-lang"
+		GCC_TESTS_CXXFLAGS+=" -Wno-complain-wrong-lang"
+
+		# Issues with Ada tests:
+		# gnat.dg/align_max.adb
+		# gnat.dg/trampoline4.adb
+		#
+		# A handful of Ada tests use -fstack-check and conflict
+		# with -fstack-clash-protection.
+		#
+		# TODO: This isn't ideal given it obv. affects codegen
+		# and we want to be sure it works.
+		GCC_TESTS_CFLAGS+=" -fno-stack-clash-protection"
+		GCC_TESTS_CXXFLAGS+=" -fno-stack-clash-protection"
+
+		# configure defaults to '-O2 -g' and some tests expect it
+		# accordingly.
+		GCC_TESTS_CFLAGS+=" -g"
+
+		# TODO: Does this handle s390 (-m31) correctly?
+		# TODO: What if there are multiple ABIs like x32 too?
+		# XXX: Disabled until validate_failures.py can handle 'variants'
+		# XXX: https://gcc.gnu.org/PR116260
+		#is_multilib && GCC_TESTS_RUNTESTFLAGS+=" --target_board=unix{,-m32}"
+
+		# nonfatal here as we die if the comparison below fails. Also, note that
+		# the exit code of targets other than 'check' may be unreliable.
+		#
+		# CFLAGS and so on are repeated here because of tests vs building test
+		# deps like libbacktrace.
+		#
+		# TODO: Should we try pass in the regular user flags for the non-RUNTESTFLAGS
+		# instances below for building e.g. libbacktrace?
+		nonfatal emake -C "${WORKDIR}"/build -k "${GCC_TESTS_CHECK_TARGET}" \
+			RUNTESTFLAGS=" \
+				${GCC_TESTS_RUNTESTFLAGS} \
+				CFLAGS_FOR_TARGET='${GCC_TESTS_CFLAGS_FOR_TARGET:-${GCC_TESTS_CFLAGS}}' \
+				CXXFLAGS_FOR_TARGET='${GCC_TESTS_CXXFLAGS_FOR_TARGET:-${GCC_TESTS_CXXFLAGS}}' \
+				LDFLAGS_FOR_TARGET='${TEST_LDFLAGS_FOR_TARGET:-${GCC_TESTS_LDFLAGS}}' \
+				CFLAGS='${GCC_TESTS_CFLAGS}' \
+				CXXFLAGS='${GCC_TESTS_CXXFLAGS}' \
+				FCFLAGS='${GCC_TESTS_FCFLAGS}' \
+				FFLAGS='${GCC_TESTS_FFLAGS}' \
+				LDFLAGS='${GCC_TESTS_LDFLAGS}' \
+			" \
+			CFLAGS_FOR_TARGET="${GCC_TESTS_CFLAGS_FOR_TARGET:-${GCC_TESTS_CFLAGS}}" \
+			CXXFLAGS_FOR_TARGET="${GCC_TESTS_CXXFLAGS_FOR_TARGET:-${GCC_TESTS_CXXFLAGS}}" \
+			LDFLAGS_FOR_TARGET="${GCC_TESTS_LDFLAGS_FOR_TARGET:-${GCC_TESTS_LDFLAGS}}" \
+			CFLAGS="${GCC_TESTS_CFLAGS}" \
+			CXXFLAGS="${GCC_TESTS_CXXFLAGS}" \
+			FCFLAGS="${GCC_TESTS_FCFLAGS}" \
+			FFLAGS="${GCC_TESTS_FFLAGS}" \
+			LDFLAGS="${GCC_TESTS_LDFLAGS}"
+	)
 
 	# Produce an updated failure manifest.
 	einfo "Generating a new failure manifest ${T}/${CHOST}.xfail"
@@ -1975,7 +2046,7 @@ toolchain_src_test() {
 			eerror "GCC_TESTS_IGNORE_NO_BASELINE is set, ignoring test result and creating a new baseline..."
 		elif [[ -n ${GCC_TESTS_REGEN_BASELINE} ]] ; then
 			eerror "GCC_TESTS_REGEN_BASELINE is set, ignoring test result and creating using a new baseline..."
-		elif [[ ${ret} != 0 ]]; then
+		elif [[ ${ret} != 0 ]] ; then
 			eerror "(Set GCC_TESTS_IGNORE_NO_BASELINE=1 to make this non-fatal and generate a baseline.)"
 			die "Tests failed (failures occurred with no reference data)"
 		fi