diff --git a/LibOS/.gitignore b/LibOS/.gitignore
index 9caf427d..9e801aa5 100644
--- a/LibOS/.gitignore
+++ b/LibOS/.gitignore
@@ -2,3 +2,8 @@
 /glibc-*.*/
 /glibc-build/
 /build.log
+
+/gcc-*.tar.gz
+/gcc-*.*.*/
+/gcc-build/
+/gcc-build.log
diff --git a/LibOS/Makefile b/LibOS/Makefile
index 5777140d..f6e7be0f 100644
--- a/LibOS/Makefile
+++ b/LibOS/Makefile
@@ -1,12 +1,27 @@
 include ../Scripts/Makefile.configs
 include ../Scripts/Makefile.rules
 
+RUNTIME_DIR = $(CURDIR)/../Runtime
+
+define LN_SF_TO_RUNTIME_DIR_template =
+$(RUNTIME_DIR)/$(notdir $(1)): $(1)
+	$$(call cmd,ln_sfr)
+endef
+
+GNU_MIRRORS ?= https://ftp.gnu.org/gnu/ \
+               https://mirrors.kernel.org/gnu/ \
+               https://mirrors.ocf.berkeley.edu/gnu/
+
+# ------------------------------------------------------------------------------------------------
+# Glibc build: patch libc.so and other C standard libraries to replace raw SYSCALL instructions
+# with function calls into Graphene (plus some smaller patches for Graphene). The resulting
+# libraries are symlinked under $RUNTIME_DIR.
+# ------------------------------------------------------------------------------------------------
 GLIBC_VERSION ?= 2.31
 GLIBC_SRC = glibc-$(GLIBC_VERSION)
-GLIBC_CHECKSUM = $(firstword $(shell grep $(GLIBC_SRC).tar.gz glibc-checksums))
+GLIBC_HASH = $(firstword $(shell grep $(GLIBC_SRC).tar.gz glibc-checksums))
 SHIM_DIR = shim
 BUILD_DIR = glibc-build
-RUNTIME_DIR = $(CURDIR)/../Runtime
 GLIBC_LIBS = \
 	csu/crt1.o \
 	csu/crti.o \
@@ -38,10 +53,6 @@ export GLIBC_CFLAGS
 all: $(GLIBC_TARGET) $(GLIBC_RUNTIME)
 	$(MAKE) -C $(SHIM_DIR) all
 
-.PHONY: format
-format:
-	$(MAKE) -C $(SHIM_DIR) format
-
 ifeq ($(findstring x86_64,$(SYS))$(findstring linux,$(SYS)),x86_64linux)
 
 .SECONDARY: $(BUILD_DIR)/Build.success
@@ -52,27 +63,18 @@ $(BUILD_DIR)/Build.success: $(BUILD_DIR)/Makefile
 
 $(GLIBC_TARGET): $(BUILD_DIR)/Build.success
 
-$(BUILD_DIR)/Makefile: $(GLIBC_SRC)/configure
+$(BUILD_DIR)/Makefile: $(GLIBC_SRC)/.configured
 	mkdir -p $(BUILD_DIR)
 	(cd $(BUILD_DIR) || exit 1; \
-	CFLAGS=$$GLIBC_CFLAGS ../$< --prefix=$(RUNTIME_DIR) \
+	CFLAGS=$$GLIBC_CFLAGS ../$(GLIBC_SRC)/configure --prefix=$(RUNTIME_DIR) \
 		--with-tls \
 		--without-selinux \
 		--disable-test \
 		--disable-nscd \
 	)
 
-define LN_SF_TO_RUNTIME_DIR_template =
-$(RUNTIME_DIR)/$(notdir $(1)): $(1)
-	$$(call cmd,ln_sfr)
-endef
-
 $(foreach lib,$(GLIBC_TARGET),$(eval $(call LN_SF_TO_RUNTIME_DIR_template,$(lib))))
 
-GLIBC_MIRRORS ?= https://ftp.gnu.org/gnu/ \
-		https://mirrors.kernel.org/gnu/ \
-		https://mirrors.ocf.berkeley.edu/gnu/
-
 GLIBC_PATCHES = \
 	glibc-patches/$(GLIBC_SRC).patch \
 	glibc-patches/syscalldb-api.patch
@@ -93,28 +95,86 @@ GLIBC_PATCHES_2.31 = \
 
 GLIBC_PATCHES += $(GLIBC_PATCHES_$(GLIBC_VERSION))
 
-$(GLIBC_SRC)/configure: $(GLIBC_PATCHES) $(GLIBC_SRC).tar.gz
+.SECONDARY: $(GLIBC_SRC)/.configured
+$(GLIBC_SRC)/.configured: $(GLIBC_PATCHES) $(GLIBC_SRC).tar.gz
 	$(RM) -r $(GLIBC_SRC)
-	tar -xzf $(GLIBC_SRC).tar.gz
+	tar -mxzf $(GLIBC_SRC).tar.gz
 	cd $(GLIBC_SRC) && \
 	for p in $(GLIBC_PATCHES); do \
 		echo applying $$p; \
-		patch -p1 < ../$$p || exit 255; \
+		patch -p1 -l < ../$$p || exit 255; \
 	done
 	touch $@
 
 $(GLIBC_SRC).tar.gz:
-	../Scripts/download --output $@ --sha256 $(GLIBC_CHECKSUM) $(foreach mirror,$(GLIBC_MIRRORS),--url $(mirror)glibc/$(GLIBC_SRC).tar.gz)
+	../Scripts/download --output $@ --sha256 $(GLIBC_HASH) $(foreach mirror,$(GNU_MIRRORS),--url $(mirror)glibc/$(GLIBC_SRC).tar.gz)
 
-$(GLIBC_SRC)/elf/Versions: $(GLIBC_SRC)/configure
+$(GLIBC_SRC)/elf/Versions: $(GLIBC_SRC)/.configured
 
-$(GLIBC_SRC)/nptl/Versions: $(GLIBC_SRC)/configure
+$(GLIBC_SRC)/nptl/Versions: $(GLIBC_SRC)/.configured
 
-$(GLIBC_SRC)/dlfcn/Versions: $(GLIBC_SRC)/configure
+$(GLIBC_SRC)/dlfcn/Versions: $(GLIBC_SRC)/.configured
 
+# ------------------------------------------------------------------------------------------------
+# GCC build: patch libgomp.so.1 (OpenMP runtime library) to replace raw SYSCALL instruction with
+# function call into Graphene. GCC is not built by default with Graphene; use `make -C LibOS gcc`
+# to build it. The resulting libgomp.so.1 is symlinked under $RUNTIME_DIR. This patched version
+# makes sense only on x86_64 platforms. NOTE: We'd prefer to build libgomp.so.1 alone but it is
+# impossible (the only way to build it is as part of the complete GCC build).
+# ------------------------------------------------------------------------------------------------
+GCC_VERSION ?= 10.2.0
+GCC_SRC = gcc-$(GCC_VERSION)
+GCC_HASH = 27e879dccc639cd7b0cc08ed575c1669492579529b53c9ff27b0b96265fa867d
+GCC_BUILD_DIR = gcc-build
+GCC_LIBS = x86_64-pc-linux-gnu/libgomp/.libs/libgomp.so.1
+GCC_TARGET = $(addprefix $(GCC_BUILD_DIR)/, $(GCC_LIBS))
+GCC_RUNTIME = $(addprefix $(RUNTIME_DIR)/, $(notdir $(GCC_TARGET)))
+
+.SECONDARY: $(GCC_BUILD_DIR)/Build.success
+
+$(GCC_BUILD_DIR)/Build.success: $(GCC_BUILD_DIR)/Makefile
+	@echo "Building gcc, may take a while to finish. Warning messages may show up. If this process terminates with failures, see \"$(GCC_BUILD_DIR)/gcc-build.log\" for more information."
+	($(MAKE) -C $(GCC_BUILD_DIR) 2>&1 > gcc-build.log) && touch $@
+
+$(GCC_TARGET): $(GCC_BUILD_DIR)/Build.success
+
+$(GCC_BUILD_DIR)/Makefile: $(GCC_SRC)/.configured
+	mkdir -p $(GCC_BUILD_DIR)
+	(cd $(GCC_BUILD_DIR) || exit 1; \
+	../$(GCC_SRC)/configure --prefix=$(RUNTIME_DIR) \
+		--enable-languages=c \
+		--disable-multilib \
+	)
+
+$(foreach lib,$(GCC_TARGET),$(eval $(call LN_SF_TO_RUNTIME_DIR_template,$(lib))))
+
+GCC_PATCHES = \
+	gcc-patches/libgomp-replace-futex-instruction.patch
+
+.SECONDARY: $(GCC_SRC)/.configured
+$(GCC_SRC)/.configured: $(GCC_PATCHES) $(GCC_SRC).tar.gz
+	$(RM) -r $(GCC_SRC)
+	tar -mxzf $(GCC_SRC).tar.gz
+	cd $(GCC_SRC) && \
+	for p in $(GCC_PATCHES); do \
+		echo applying $$p; \
+		patch -p1 -l < ../$$p || exit 255; \
+	done
+	cd $(GCC_SRC) && ./contrib/download_prerequisites
+	touch $@
+
+$(GCC_SRC).tar.gz:
+	../Scripts/download --output $@ --sha256 $(GCC_HASH) $(foreach mirror,$(GNU_MIRRORS),--url $(mirror)gcc/$(GCC_SRC)/$(GCC_SRC).tar.gz)
+
+.PHONY: gcc
+gcc: $(GCC_TARGET) $(GCC_RUNTIME)
+
+# ------------------------------------------------------------------------------------------------
+# Common targets
+# ------------------------------------------------------------------------------------------------
 .PHONY: clean_
 clean_:
-	$(RM) -r $(BUILD_DIR) $(GLIBC_SRC) build.log
+	$(RM) -r $(BUILD_DIR) $(GLIBC_SRC) $(GCC_BUILD_DIR) $(GCC_SRC) build.log gcc-build.log
 
 .PHONY: clean
 clean: clean_
@@ -123,20 +183,27 @@ clean: clean_
 .PHONY: distclean
 distclean: clean_
 	$(MAKE) -C $(SHIM_DIR) distclean
-	$(RM) $(GLIBC_SRC).tar.gz
+	$(RM) $(GLIBC_SRC).tar.gz $(GCC_SRC).tar.gz
 
 else
 .IGNORE: $(GLIBC_TARGET)
 $(GLIBC_TARGET):
 
+.IGNORE: $(GCC_TARGET)
+$(GCC_TARGET):
+
 .PHONY: clean
 clean:
-	$(RM) -r $(BUILD_DIR)
+	$(RM) -r $(BUILD_DIR) $(GCC_BUILD_DIR)
 
 .PHONY: distclean
 distclean: clean
 endif
 
+.PHONY: format
+format:
+	$(MAKE) -C $(SHIM_DIR) format
+
 .PHONY: test
 test:
 	$(MAKE) -C $(SHIM_DIR) test
diff --git a/LibOS/gcc-patches/libgomp-replace-futex-instruction.patch b/LibOS/gcc-patches/libgomp-replace-futex-instruction.patch
new file mode 100644
index 00000000..c964ab90
--- /dev/null
+++ b/LibOS/gcc-patches/libgomp-replace-futex-instruction.patch
@@ -0,0 +1,49 @@
+diff --git a/libgomp/config/linux/x86/futex.h b/libgomp/config/linux/x86/futex.h
+index ead74d1496736a49694ef6b9b2b4da50f9852664..3c82859ad8b82a09ec95f720727937ee5a2863c1 100644
+--- a/libgomp/config/linux/x86/futex.h
++++ b/libgomp/config/linux/x86/futex.h
+@@ -30,13 +30,16 @@
+ #  define SYS_futex	202
+ # endif
+ 
++asm (".weak syscalldb\r\n"
++     ".type syscalldb, @function\r\n");
++
+ static inline void
+ futex_wait (int *addr, int val)
+ {
+   long res;
+ 
+   register long r10 __asm__("%r10") = 0;
+-  __asm volatile ("syscall"
++  __asm volatile ("subq $128, %%rsp; callq *syscalldb@GOTPCREL(%%rip); addq $128, %%rsp;"
+ 		  : "=a" (res)
+ 		  : "0" (SYS_futex), "D" (addr), "S" (gomp_futex_wait),
+ 		    "d" (val), "r" (r10)
+@@ -45,7 +48,7 @@ futex_wait (int *addr, int val)
+     {
+       gomp_futex_wait &= ~FUTEX_PRIVATE_FLAG;
+       gomp_futex_wake &= ~FUTEX_PRIVATE_FLAG;
+-      __asm volatile ("syscall"
++      __asm volatile ("subq $128, %%rsp; callq *syscalldb@GOTPCREL(%%rip); addq $128, %%rsp;"
+ 		      : "=a" (res)
+ 		      : "0" (SYS_futex), "D" (addr), "S" (gomp_futex_wait),
+ 			"d" (val), "r" (r10)
+@@ -58,7 +61,7 @@ futex_wake (int *addr, int count)
+ {
+   long res;
+ 
+-  __asm volatile ("syscall"
++  __asm volatile ("subq $128, %%rsp; callq *syscalldb@GOTPCREL(%%rip); addq $128, %%rsp;"
+ 		  : "=a" (res)
+ 		  : "0" (SYS_futex), "D" (addr), "S" (gomp_futex_wake),
+ 		    "d" (count)
+@@ -67,7 +70,7 @@ futex_wake (int *addr, int count)
+     {
+       gomp_futex_wait &= ~FUTEX_PRIVATE_FLAG;
+       gomp_futex_wake &= ~FUTEX_PRIVATE_FLAG;
+-      __asm volatile ("syscall"
++      __asm volatile ("subq $128, %%rsp; callq *syscalldb@GOTPCREL(%%rip); addq $128, %%rsp;"
+ 		      : "=a" (res)
+ 		      : "0" (SYS_futex), "D" (addr), "S" (gomp_futex_wake),
+ 			"d" (count)
diff --git a/LibOS/shim/test/regression/openmp.manifest.template b/LibOS/shim/test/regression/openmp.manifest.template
index f3dae162..dbc85cef 100644
--- a/LibOS/shim/test/regression/openmp.manifest.template
+++ b/LibOS/shim/test/regression/openmp.manifest.template
@@ -22,6 +22,14 @@ sgx.trusted_files.ld = file:../../../../Runtime/ld-linux-x86-64.so.2
 sgx.trusted_files.libc = file:../../../../Runtime/libc.so.6
 sgx.trusted_files.libpthread = file:../../../../Runtime/libpthread.so.0
 sgx.trusted_files.libdl = file:../../../../Runtime/libdl.so.2
-sgx.trusted_files.libgomp = file:/usr$(ARCH_LIBDIR)/libgomp.so.1
+
+sgx.trusted_files.libgomp_native = file:/usr$(ARCH_LIBDIR)/libgomp.so.1
+
+# Graphene optionally provides patched OpenMP runtime library that runs faster
+# inside SGX enclaves (execute `make -C LibOS gcc` to generate it). Uncomment
+# the line below to use the patched library. This library will replace the
+# native one because Graphene's Runtime path has priority in LD_LIBRARY_PATH.
+
+#sgx.trusted_files.libgomp_graphene = file:../../../../Runtime/libgomp.so.1
 
 sgx.static_address = 1