picolibc: Add default syscall implementations [v2]

picolibc: Use thread_getpid for getpid() in picolibc_syscalls_default

Instead of directly accessing the sched_active_pid variable (which
isn't defined in this context), use the existing wrapper function
to get that value.

Signed-off-by: Keith Packard <keithp@keithp.com>

---
v2:
	Squash a couple of fixes in

	* fixup! picolibc: Use thread_getpid for getpid() in
          picolibc_syscalls_default

	* squashme: Add `times` to picolibc syscalls

	* Add __noreturn__ attribute to _exit

	* Add VFS syscall wrappers. This provides the POSIX api used
          by picolibc stdio

sys/picolibc_syscalls_default/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

sys/picolibc_syscalls_default/Makefile.include

@@ -0,0 +1 @@
+UNDEF += $(BINDIR)/picolibc_syscalls_default/syscalls.o

sys/picolibc_syscalls_default/syscalls.c

@@ -0,0 +1,328 @@
+/*
+ * Copyright (C) 2019 Koen Zandberg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+/**
+ * @defgroup    sys_picolibc PicoLibc system call
+ * @ingroup     sys
+ * @brief       PicoLibc system call
+ * @{
+ *
+ * @file
+ * @brief       PicoLibc system call implementations
+ *
+ * @author      Koen Zandberg <koen@bergzand.net>
+ *
+ * @}
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <sys/times.h>
+
+#include "log.h"
+#include "periph/pm.h"
+#include "stdio_base.h"
+
+uint8_t sbrk[1];
+
+/**
+ * @brief Exit a program without cleaning up files
+ *
+ * If your system doesn't provide this, it is best to avoid linking with subroutines that
+ * require it (exit, system).
+ *
+ * @param n     the exit code, 0 for all OK, >0 for not OK
+ */
+void __attribute__((__noreturn__))
+_exit(int n)
+{
+    LOG_INFO("#! exit %i: powering off\n", n);
+    pm_off();
+    while(1);
+}
+
+/**
+ * @brief Send a signal to a thread
+ *
+ * @param[in] pid the pid to send to
+ * @param[in] sig the signal to send
+ *
+ * @return    always returns -1 to signal error
+ */
+__attribute__ ((weak))
+int kill(pid_t pid, int sig)
+{
+    (void) pid;
+    (void) sig;
+    errno = ESRCH;                         /* not implemented yet */
+    return -1;
+}
+
+/* File descriptor pointers */
+int picolibc_get(FILE *file)
+{
+    (void)file;
+    char c = 0;
+    stdio_read(&c, 1);
+    return c;
+}
+
+int picolibc_put(char c, FILE *file)
+{
+    (void)file;
+    stdio_write(&c, 1);
+    return 1;
+}
+FILE picolibc_stdio =
+    FDEV_SETUP_STREAM(picolibc_put, picolibc_get, NULL, _FDEV_SETUP_RW);
+
+FILE *const __iob[] = {
+    &picolibc_stdio,    /* stdin  */
+    &picolibc_stdio,    /* stdout */
+    &picolibc_stdio,    /* stderr */
+};
+
+#include <thread.h>
+/**
+ * @brief Get the process-ID of the current thread
+ *
+ * @return      the process ID of the current thread
+ */
+pid_t getpid(void)
+{
+    return thread_getpid();
+}
+
+#if MODULE_VFS
+#include "vfs.h"
+
+/**
+ * @brief Open a file
+ *
+ * This is a wrapper around @c vfs_open
+ *
+ * @param name  file name to open
+ * @param flags flags, see man 3p open
+ * @param mode  mode, file creation mode if the file is created when opening
+ *
+ * @return      fd number (>= 0) on success
+ * @return      -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int open(const char *name, int flags, int mode)
+{
+    int fd = vfs_open(name, flags, mode);
+    if (fd < 0) {
+        /* vfs returns negative error codes */
+        errno = -fd;
+        return -1;
+    }
+    return fd;
+}
+
+/**
+ * @brief Read bytes from an open file
+ *
+ * This is a wrapper around @c vfs_read
+ *
+ * @param[in]  fd     open file descriptor obtained from @c open()
+ * @param[out] dest   destination buffer
+ * @param[in]  count  maximum number of bytes to read
+ *
+ * @return       number of bytes read on success
+ * @return       -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+_READ_WRITE_RETURN_TYPE read(int fd, void *dest, size_t count)
+{
+    int res = vfs_read(fd, dest, count);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return res;
+}
+
+/**
+ * @brief Write bytes to an open file
+ *
+ * This is a wrapper around @c vfs_write
+ *
+ * @param[in]  fd     open file descriptor obtained from @c open()
+ * @param[in]  src    source data buffer
+ * @param[in]  count  maximum number of bytes to write
+ *
+ * @return       number of bytes written on success
+ * @return       -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+_READ_WRITE_RETURN_TYPE write(int fd, const void *src, size_t count)
+{
+    int res = vfs_write(fd, src, count);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return res;
+}
+
+/**
+ * @brief Close an open file
+ *
+ * This is a wrapper around @c vfs_close
+ *
+ * If this call returns an error, the fd should still be considered invalid and
+ * no further attempt to use it shall be made, not even to retry @c close()
+ *
+ * @param[in]  fd     open file descriptor obtained from @c open()
+ *
+ * @return       0 on success
+ * @return       -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int close(int fd)
+{
+    int res = vfs_close(fd);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return res;
+}
+
+/**
+ * Current process times (not implemented).
+ *
+ * @param[out]  ptms    Not modified.
+ *
+ * @return  -1, this function always fails. errno is set to ENOSYS.
+ */
+clock_t times(struct tms *ptms)
+{
+    (void)ptms;
+    errno = ENOSYS;
+
+    return (-1);
+}
+
+/**
+ * @brief Query or set options on an open file
+ *
+ * This is a wrapper around @c vfs_fcntl
+ *
+ * @param[in]  fd     open file descriptor obtained from @c open()
+ * @param[in]  cmd    fcntl command, see man 3p fcntl
+ * @param[in]  arg    argument to fcntl command, see man 3p fcntl
+ *
+ * @return       0 on success
+ * @return       -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int fcntl (int fd, int cmd, int arg)
+{
+    int res = vfs_fcntl(fd, cmd, arg);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return res;
+}
+
+/**
+ * @brief Seek to position in file
+ *
+ * This is a wrapper around @c vfs_lseek
+ *
+ * @p whence determines the function of the seek and should be set to one of
+ * the following values:
+ *
+ *  - @c SEEK_SET: Seek to absolute offset @p off
+ *  - @c SEEK_CUR: Seek to current location + @p off
+ *  - @c SEEK_END: Seek to end of file + @p off
+ *
+ * @param[in]  fd       open file descriptor obtained from @c open()
+ * @param[in]  off      seek offset
+ * @param[in]  whence   determines the seek method, see detailed description
+ *
+ * @return the new seek location in the file on success
+ * @return -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+off_t lseek(int fd, _off_t off, int whence)
+{
+    int res = vfs_lseek(fd, off, whence);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return res;
+}
+
+/**
+ * @brief Get status of an open file
+ *
+ * This is a wrapper around @c vfs_fstat
+ *
+ * @param[in]  fd       open file descriptor obtained from @c open()
+ * @param[out] buf      pointer to stat struct to fill
+ *
+ * @return 0 on success
+ * @return -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int fstat(int fd, struct stat *buf)
+{
+    int res = vfs_fstat(fd, buf);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return 0;
+}
+
+/**
+ * @brief Status of a file (by name)
+ *
+ * This is a wrapper around @c vfs_fstat
+ *
+ * @param[in]  name     path to file
+ * @param[out] buf      pointer to stat struct to fill
+ *
+ * @return 0 on success
+ * @return -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int stat(const char *name, struct stat *st)
+{
+    int res = vfs_stat(name, st);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return 0;
+}
+
+/**
+ * @brief  Unlink (delete) a file
+ *
+ * @param[in]  path     path to file to be deleted
+ *
+ * @return 0 on success
+ * @return -1 on error, @c errno set to a constant from errno.h to indicate the error
+ */
+int unlink(const char *path)
+{
+    int res = vfs_unlink(path);
+    if (res < 0) {
+        /* vfs returns negative error codes */
+        errno = -res;
+        return -1;
+    }
+    return 0;
+}
+
+#endif /* MODULE_VFS */