[PATCH v3 liburing 3/3] configure: Add `CONFIG_NOLIBC` variable and macro

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

It's for conditonal variable and macro to enable nolibc build.
Also add `--nolibc` option to `configure` to enable it.

Link: https://github.com/axboe/liburing/issues/443
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ammar Faizi <ammar.faizi@students.amikom.ac.id>
---
 configure    |  9 +++++++++
 src/Makefile | 17 ++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 92f51bd..d2866b3 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 '$0 --help' for more information"
@@ -71,6 +73,7 @@ Options: [defaults in brackets after descriptions]
   --datadir=PATH           install shared data in PATH [$datadir]
   --cc=CMD                 use CMD as the C compiler
   --cxx=CMD                use CMD as the C++ compiler
+  --nolibc                 build liburing without libc
 EOF
 exit 0
 fi
@@ -358,6 +361,12 @@ 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..09ff395 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 -nodefaultlibs -ffreestanding -fno-stack-protector
+	override CPPFLAGS += -nostdlib -nodefaultlibs -ffreestanding -fno-stack-protector
+	override LINK_FLAGS += -nostdlib -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
@@ -73,3 +84,7 @@ clean:
 	@rm -f $(all_targets) $(liburing_objs) $(liburing_sobjs) $(soname).new
 	@rm -f *.so* *.a *.o
 	@rm -f include/liburing/compat.h
+
+	@# When cleaning, we don't include ../config-host.mak,
+	@# so the nolibc objects are always skipped, clean them up!
+	@rm -f nolibc.ol nolibc.os
-- 
2.30.2