[PATCH v2 liburing 4/4] Add CONFIG_NOLIBC variable and macro

[Ammar Faizi <ammar.faizi@students.amikom.ac.id>]

For conditonal variable and macro to enable nolibc build.
Add `--nolibc` option for `configure` to enable it.

Link: https://github.com/axboe/liburing/issues/443
Signed-off-by: Ammar Faizi <ammar.faizi@students.amikom.ac.id>
---
 configure    |  8 ++++++++
 src/Makefile | 13 ++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 92f51bd..6712ce3 100755
--- a/configure
+++ b/configure
@@ -24,6 +24,8 @@ for opt do
   ;;
   --cxx=*) cxx="$optarg"
   ;;
+  --nolibc) liburing_nolibc="yes"
+  ;;
   *)
     echo "ERROR: unknown option $opt"
     echo "Try '$0 --help' for more information"
@@ -358,6 +360,12 @@ print_config "has_memfd_create" "$has_memfd_create"
 
 
 #############################################################################
+if test "$liburing_nolibc" = "yes"; then
+  output_sym "CONFIG_NOLIBC"
+else
+  liburing_nolibc="no"
+fi
+print_config "liburing_nolibc" "$liburing_nolibc"
 
 if test "$__kernel_rwf_t" = "yes"; then
   output_sym "CONFIG_HAVE_KERNEL_RWF_T"
diff --git a/src/Makefile b/src/Makefile
index 5e46a9d..290517d 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -32,11 +32,22 @@ endif
 
 all: $(all_targets)
 
-liburing_srcs := setup.c queue.c syscall.c register.c
+liburing_srcs := setup.c queue.c register.c
+
+ifeq ($(CONFIG_NOLIBC),y)
+	liburing_srcs += nolibc.c
+	override CFLAGS += -nostdlib -nolibc -nodefaultlibs -ffreestanding -fno-stack-protector
+	override CPPFLAGS += -nostdlib -nolibc -nodefaultlibs -ffreestanding -fno-stack-protector
+	override LINK_FLAGS += -nostdlib -nolibc -nodefaultlibs
+else
+	liburing_srcs += syscall.c
+endif
 
 liburing_objs := $(patsubst %.c,%.ol,$(liburing_srcs))
 liburing_sobjs := $(patsubst %.c,%.os,$(liburing_srcs))
 
+$(liburing_srcs): syscall.h lib.h
+
 $(liburing_objs) $(liburing_sobjs): include/liburing/io_uring.h
 
 %.os: %.c
-- 
2.30.2