[RFC PATCH v2 4/8] tools/nolibc/sys: Implement `mmap()` and `munmap()`

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

Implement mmap() and munmap(). Currently, they are only available for
architecures that have my_syscall6 macro. For architectures that don't
have, this function will return -1 with errno set to ENOSYS (Function
not implemented).

This has been tested on x86 and i386.

Notes for i386:
 1) The common mmap() syscall implementation uses __NR_mmap2 instead
    of __NR_mmap.

 2) The offset must be shifted-right by 12-bit.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

@@ Changelog:

   Link RFC v1: https://lore.kernel.org/lkml/20220320093750.159991-5-ammarfaizi2@gnuweeb.org/
   RFC v1 -> RFC v2:
    * No changes *
---
 tools/include/nolibc/sys.h | 62 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
index 4d4308d5d111..08491070387b 100644
--- a/tools/include/nolibc/sys.h
+++ b/tools/include/nolibc/sys.h
@@ -14,6 +14,7 @@
 #include <asm/unistd.h>
 #include <asm/signal.h>  // for SIGCHLD
 #include <asm/ioctls.h>
+#include <asm/mman.h>
 #include <linux/fs.h>
 #include <linux/loop.h>
 #include <linux/time.h>
@@ -675,6 +676,67 @@ int mknod(const char *path, mode_t mode, dev_t dev)
 	return ret;
 }
 
+#ifndef MAP_SHARED
+#define MAP_SHARED		0x01	/* Share changes */
+#define MAP_PRIVATE		0x02	/* Changes are private */
+#define MAP_SHARED_VALIDATE	0x03	/* share + validate extension flags */
+#endif
+
+#ifndef MAP_FAILED
+#define MAP_FAILED ((void *)-1)
+#endif
+
+static __attribute__((unused))
+void *sys_mmap(void *addr, size_t length, int prot, int flags, int fd,
+	       off_t offset)
+{
+#ifndef my_syscall6
+	/* Function not implemented. */
+	return -ENOSYS;
+#else
+
+	int n;
+
+#if defined(__i386__)
+	n = __NR_mmap2;
+	offset >>= 12;
+#else
+	n = __NR_mmap;
+#endif
+
+	return (void *)my_syscall6(n, addr, length, prot, flags, fd, offset);
+#endif
+}
+
+static __attribute__((unused))
+void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset)
+{
+	void *ret = sys_mmap(addr, length, prot, flags, fd, offset);
+
+	if ((unsigned long)ret >= -4095UL) {
+		SET_ERRNO(-(long)ret);
+		ret = MAP_FAILED;
+	}
+	return ret;
+}
+
+static __attribute__((unused))
+int sys_munmap(void *addr, size_t length)
+{
+	return my_syscall2(__NR_munmap, addr, length);
+}
+
+static __attribute__((unused))
+int munmap(void *addr, size_t length)
+{
+	int ret = sys_munmap(addr, length);
+
+	if (ret < 0) {
+		SET_ERRNO(-ret);
+		ret = -1;
+	}
+	return ret;
+}
 
 /*
  * int mount(const char *source, const char *target,
-- 
Ammar Faizi