[PATCH v2 RFC liburing 4/5] Add no libc build support

[Ammar Faizi <ammar.faizi@xxxxxxxxxxxxxxxxxxxxx>]

Create `src/nolibc.c` to substitute libc functions like `memset()`,
`malloc()` and `free()`. Only build this file when we build liburing
without libc.

Wrap libc functions with `static inline` functions, defined in
`src/lib.h`, currently we have:
 1) `get_page_size`
 2) `uring_memset`
 3) `uring_malloc`
 4) `uring_free`

Add conditional preprocessor in `src/{syscall,lib}.h` to use arch
dependent and nolibc functions when we build liburing without libc.

Extra notes for tests:
 1) Functions in `src/syscall.c` require libc to work.
 2) Tests require functions in `src/syscall.c`.

So we build `src/syscall.c` manually from test's Makefile.

The Makefile in `src/` dir still builds `src/syscall.c` when we
compile liburing with libc.

Link: https://github.com/axboe/liburing/issues/443
Signed-off-by: Ammar Faizi <ammar.faizi@xxxxxxxxxxxxxxxxxxxxx>
---
 src/lib.h      | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/nolibc.c   | 48 +++++++++++++++++++++++++++++++
 src/queue.c    | 14 ++-------
 src/register.c | 12 ++------
 src/setup.c    | 30 +++++++-------------
 src/syscall.c  | 11 +++++++-
 src/syscall.h  | 71 ++++++++++++++++++++++++++++++++++++----------
 test/Makefile  | 19 ++++++++++---
 8 files changed, 222 insertions(+), 60 deletions(-)
 create mode 100644 src/lib.h
 create mode 100644 src/nolibc.c

diff --git a/src/lib.h b/src/lib.h
new file mode 100644
index 0000000..baacabe
--- /dev/null
+++ b/src/lib.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: MIT */
+#ifndef LIBURING_LIB_H
+#define LIBURING_LIB_H
+
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#ifdef LIBURING_NOLIBC
+#  if defined(__x86_64__) || defined(__i386__)
+#    include "arch/x86/lib.h"
+#  else
+#    error "The arch is currently not supported to build liburing without libc"
+#  endif
+#endif
+
+#ifndef offsetof
+# define offsetof(TYPE, FIELD) ((size_t) &((TYPE *)0)->FIELD)
+#endif
+
+#ifndef container_of
+# define container_of(PTR, TYPE, FIELD) ({				\
+	__typeof__(((TYPE *)0)->FIELD) *__FIELD_PTR = (PTR);		\
+	(TYPE *)((char *) __FIELD_PTR - offsetof(TYPE, FIELD));		\
+})
+#endif
+
+
+static inline long get_page_size(void)
+{
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_get_page_size();
+#else
+	long page_size;
+
+	page_size = sysconf(_SC_PAGESIZE);
+	if (page_size < 0)
+		page_size = 4096;
+
+	return page_size;
+#endif
+}
+
+void *__uring_memset(void *s, int c, size_t n);
+
+static inline void *uring_memset(void *s, int c, size_t n)
+{
+#ifdef LIBURING_NOLIBC
+	return __uring_memset(s, c, n);
+#else
+	return memset(s, c, n);
+#endif
+}
+
+void *__uring_malloc(size_t len);
+
+static inline void *uring_malloc(size_t len)
+{
+#ifdef LIBURING_NOLIBC
+	return __uring_malloc(len);
+#else
+	return malloc(len);
+#endif
+}
+
+void __uring_free(void *p);
+
+static inline void uring_free(void *p)
+{
+#ifdef LIBURING_NOLIBC
+	__uring_free(p);
+#else
+	free(p);
+#endif
+}
+
+#endif /* #ifndef LIBURING_LIB_H */
diff --git a/src/nolibc.c b/src/nolibc.c
new file mode 100644
index 0000000..149426c
--- /dev/null
+++ b/src/nolibc.c
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: MIT */
+
+#ifndef LIBURING_NOLIBC
+# error "This file should only be compiled for no libc build"
+#endif
+
+#include "lib.h"
+#include "syscall.h"
+
+void *__uring_memset(void *s, int c, size_t n)
+{
+	size_t i;
+	unsigned char *p = s;
+
+	for (i = 0; i < n; i++)
+		p[i] = (unsigned char) c;
+
+	return s;
+}
+
+struct uring_heap {
+	size_t		len;
+	char		user_p[];
+};
+
+void *__uring_malloc(size_t len)
+{
+	struct uring_heap *heap;
+
+	heap = uring_mmap(NULL, sizeof(*heap) + len, PROT_READ | PROT_WRITE,
+			  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (IS_ERR(heap))
+		return NULL;
+
+	heap->len = sizeof(*heap) + len;
+	return heap->user_p;
+}
+
+void __uring_free(void *p)
+{
+	struct uring_heap *heap;
+
+	if (uring_unlikely(!p))
+		return;
+
+	heap = container_of(p, struct uring_heap, user_p);
+	uring_munmap(heap, heap->len);
+}
diff --git a/src/queue.c b/src/queue.c
index 9af29d5..eb0c736 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -1,19 +1,11 @@
 /* SPDX-License-Identifier: MIT */
 #define _POSIX_C_SOURCE 200112L
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/mman.h>
-#include <unistd.h>
-#include <string.h>
-#include <stdbool.h>
-
+#include "lib.h"
+#include "syscall.h"
+#include "liburing.h"
 #include "liburing/compat.h"
 #include "liburing/io_uring.h"
-#include "liburing.h"
-#include "liburing/barrier.h"
-
-#include "syscall.h"
 
 /*
  * Returns true if we're not using SQ thread (thus nobody submits but us)
diff --git a/src/register.c b/src/register.c
index 074223f..1f2c409 100644
--- a/src/register.c
+++ b/src/register.c
@@ -1,18 +1,12 @@
 /* SPDX-License-Identifier: MIT */
 #define _POSIX_C_SOURCE 200112L
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/mman.h>
-#include <sys/resource.h>
-#include <unistd.h>
-#include <string.h>
-
+#include "lib.h"
+#include "syscall.h"
+#include "liburing.h"
 #include "liburing/compat.h"
 #include "liburing/io_uring.h"
-#include "liburing.h"
 
-#include "syscall.h"
 
 int io_uring_register_buffers_update_tag(struct io_uring *ring, unsigned off,
 					 const struct iovec *iovecs,
diff --git a/src/setup.c b/src/setup.c
index 4f006de..700dc07 100644
--- a/src/setup.c
+++ b/src/setup.c
@@ -1,18 +1,11 @@
 /* SPDX-License-Identifier: MIT */
 #define _DEFAULT_SOURCE
 
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <unistd.h>
-#include <string.h>
-#include <stdlib.h>
-#include <signal.h>
-
+#include "lib.h"
+#include "syscall.h"
+#include "liburing.h"
 #include "liburing/compat.h"
 #include "liburing/io_uring.h"
-#include "liburing.h"
-
-#include "syscall.h"
 
 static void io_uring_unmap_rings(struct io_uring_sq *sq, struct io_uring_cq *cq)
 {
@@ -93,7 +86,7 @@ int io_uring_queue_mmap(int fd, struct io_uring_params *p, struct io_uring *ring
 {
 	int ret;
 
-	memset(ring, 0, sizeof(*ring));
+	uring_memset(ring, 0, sizeof(*ring));
 	ret = io_uring_mmap(fd, p, &ring->sq, &ring->cq);
 	if (!ret) {
 		ring->flags = p->flags;
@@ -161,7 +154,7 @@ int io_uring_queue_init(unsigned entries, struct io_uring *ring, unsigned flags)
 {
 	struct io_uring_params p;
 
-	memset(&p, 0, sizeof(p));
+	uring_memset(&p, 0, sizeof(p));
 	p.flags = flags;
 
 	return io_uring_queue_init_params(entries, ring, &p);
@@ -184,16 +177,16 @@ struct io_uring_probe *io_uring_get_probe_ring(struct io_uring *ring)
 	int r;
 
 	len = sizeof(*probe) + 256 * sizeof(struct io_uring_probe_op);
-	probe = malloc(len);
+	probe = uring_malloc(len);
 	if (!probe)
 		return NULL;
-	memset(probe, 0, len);
+	uring_memset(probe, 0, len);
 
 	r = io_uring_register_probe(ring, probe, 256);
 	if (r >= 0)
 		return probe;
 
-	free(probe);
+	uring_free(probe);
 	return NULL;
 }
 
@@ -214,7 +207,7 @@ struct io_uring_probe *io_uring_get_probe(void)
 
 void io_uring_free_probe(struct io_uring_probe *probe)
 {
-	free(probe);
+	uring_free(probe);
 }
 
 static int __fls(int x)
@@ -336,10 +329,7 @@ ssize_t io_uring_mlock_size_params(unsigned entries, struct io_uring_params *p)
 		cq_entries = 2 * entries;
 	}
 
-	page_size = sysconf(_SC_PAGESIZE);
-	if (page_size < 0)
-		page_size = 4096;
-
+	page_size = get_page_size();
 	return rings_size(entries, cq_entries, page_size);
 }
 
diff --git a/src/syscall.c b/src/syscall.c
index 5923fbb..cfb3ee2 100644
--- a/src/syscall.c
+++ b/src/syscall.c
@@ -1,6 +1,16 @@
 /* SPDX-License-Identifier: MIT */
 #define _DEFAULT_SOURCE
 
+/*
+ * Functions in this file require libc, only build them when we use libc.
+ *
+ * Note:
+ * liburing's tests still need these functions.
+ */
+#if defined(LIBURING_NOLIBC) && !defined(LIBURING_BUILD_TEST)
+# error "This file should only be compiled for libc build"
+#endif
+
 /*
  * Will go away once libc support is there
  */
@@ -11,7 +21,6 @@
 #include "liburing/io_uring.h"
 #include "syscall.h"
 
-
 int __sys_io_uring_register(int fd, unsigned opcode, const void *arg,
 			    unsigned nr_args)
 {
diff --git a/src/syscall.h b/src/syscall.h
index 9eff968..82f5db0 100644
--- a/src/syscall.h
+++ b/src/syscall.h
@@ -29,13 +29,13 @@
 # endif
 #elif defined __mips__
 # ifndef __NR_io_uring_setup
-#  define __NR_io_uring_setup           (__NR_Linux + 425)
+#  define __NR_io_uring_setup		(__NR_Linux + 425)
 # endif
 # ifndef __NR_io_uring_enter
-#  define __NR_io_uring_enter           (__NR_Linux + 426)
+#  define __NR_io_uring_enter		(__NR_Linux + 426)
 # endif
 # ifndef __NR_io_uring_register
-#  define __NR_io_uring_register        (__NR_Linux + 427)
+#  define __NR_io_uring_register	(__NR_Linux + 427)
 # endif
 #else /* !__alpha__ and !__mips__ */
 # ifndef __NR_io_uring_setup
@@ -49,9 +49,22 @@
 # endif
 #endif
 
-
+/*
+ * Don't put this below the #include "arch/$arch/syscall.h", that
+ * file may need it.
+ */
 struct io_uring_params;
 
+
+#ifdef LIBURING_NOLIBC
+#  if defined(__x86_64__) || defined(__i386__)
+#    include "arch/x86/syscall.h"
+#  else
+#    error "The arch is currently not supported to build liburing without libc"
+#  endif
+#endif
+
+
 /*
  * System calls
  */
@@ -68,12 +81,12 @@ static inline void *ERR_PTR(intptr_t n)
 	return (void *) n;
 }
 
-static inline intptr_t PTR_ERR(void *ptr)
+static inline intptr_t PTR_ERR(const void *ptr)
 {
 	return (intptr_t) ptr;
 }
 
-static inline bool IS_ERR(void *ptr)
+static inline bool IS_ERR(const void *ptr)
 {
 	return uring_unlikely((uintptr_t) ptr >= (uintptr_t) -4095UL);
 }
@@ -81,30 +94,40 @@ static inline bool IS_ERR(void *ptr)
 static inline int ____sys_io_uring_register(int fd, unsigned opcode,
 					    const void *arg, unsigned nr_args)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_io_uring_register(fd, opcode, arg, nr_args);
+#else
 	int ret;
-
 	ret = syscall(__NR_io_uring_register, fd, opcode, arg, nr_args);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int ____sys_io_uring_setup(unsigned entries,
 					 struct io_uring_params *p)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_io_uring_setup(entries, p);
+#else
 	int ret;
-
 	ret = syscall(__NR_io_uring_setup, entries, p);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int ____sys_io_uring_enter2(int fd, unsigned to_submit,
 					  unsigned min_complete, unsigned flags,
 					  sigset_t *sig, int sz)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_io_uring_enter(fd, to_submit, min_complete, flags,
+					  sig, sz);
+#else
 	int ret;
-
 	ret = syscall(__NR_io_uring_enter, fd, to_submit, min_complete, flags,
 		      sig, sz);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int ____sys_io_uring_enter(int fd, unsigned to_submit,
@@ -118,50 +141,68 @@ static inline int ____sys_io_uring_enter(int fd, unsigned to_submit,
 static inline void *uring_mmap(void *addr, size_t length, int prot, int flags,
 			       int fd, off_t offset)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_mmap(addr, length, prot, flags, fd, offset);
+#else
 	void *ret;
-
 	ret = mmap(addr, length, prot, flags, fd, offset);
 	return (ret == MAP_FAILED) ? ERR_PTR(-errno) : ret;
+#endif
 }
 
 static inline int uring_munmap(void *addr, size_t length)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_munmap(addr, length);
+#else
 	int ret;
-
 	ret = munmap(addr, length);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int uring_madvise(void *addr, size_t length, int advice)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_madvise(addr, length, advice);
+#else
 	int ret;
-
 	ret = madvise(addr, length, advice);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int uring_getrlimit(int resource, struct rlimit *rlim)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_getrlimit(resource, rlim);
+#else
 	int ret;
-
 	ret = getrlimit(resource, rlim);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int uring_setrlimit(int resource, const struct rlimit *rlim)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_setrlimit(resource, rlim);
+#else
 	int ret;
-
 	ret = setrlimit(resource, rlim);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 static inline int uring_close(int fd)
 {
+#ifdef LIBURING_NOLIBC
+	return __arch_impl_close(fd);
+#else
 	int ret;
-
 	ret = close(fd);
 	return (ret < 0) ? -errno : ret;
+#endif
 }
 
 #endif
diff --git a/test/Makefile b/test/Makefile
index 2936469..1a10a24 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -21,8 +21,8 @@ ifdef CONFIG_HAVE_ARRAY_BOUNDS
 endif
 
 CXXFLAGS ?= $(CFLAGS)
-override CFLAGS += $(XCFLAGS)
-override CXXFLAGS += $(XCFLAGS) -std=c++11
+override CFLAGS += $(XCFLAGS) -DLIBURING_BUILD_TEST
+override CXXFLAGS += $(XCFLAGS) -std=c++11 -DLIBURING_BUILD_TEST
 LDFLAGS ?=
 override LDFLAGS += -L../src/ -luring
 
@@ -153,11 +153,22 @@ test_targets += sq-full-cpp
 endif
 all_targets += sq-full-cpp
 
-helpers = helpers.o
+#
+# Build ../src/syscall.c manually from test's Makefile to support
+# liburing nolibc.
+#
+# Functions in ../src/syscall.c require libc to work with, if we
+# build liburing without libc, we don't have those functions
+# in liburing.a. So build it manually here.
+#
+helpers = helpers.o ../src/syscall.o
 
 all: ${helpers} $(test_targets)
 
-helpers.o: helpers.c helpers.c
+../src/syscall.o: ../src/syscall.c
+	$(QUIET_CC)$(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $<
+
+helpers.o: helpers.c
 	$(QUIET_CC)$(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $<
 
 %: %.c ${helpers} helpers.h
-- 
2.30.2