syscalls.c

// An extremely minimalist syscalls.c for newlib
// Based on riscv newlib libgloss/riscv/sys_*.c
// Written by Clifford Wolf.

#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>

#define UNIMPL_FUNC(_f) ".globl " #_f "\n.type " #_f ", @function\n" #_f ":\n"

asm (
	".text\n"
	".align 2\n"
	UNIMPL_FUNC(_open)
	UNIMPL_FUNC(_openat)
	UNIMPL_FUNC(_lseek)
	UNIMPL_FUNC(_stat)
	UNIMPL_FUNC(_lstat)
	UNIMPL_FUNC(_fstatat)
	UNIMPL_FUNC(_isatty)
	UNIMPL_FUNC(_access)
	UNIMPL_FUNC(_faccessat)
	UNIMPL_FUNC(_link)
	UNIMPL_FUNC(_unlink)
	UNIMPL_FUNC(_execve)
	UNIMPL_FUNC(_getpid)
	UNIMPL_FUNC(_fork)
	UNIMPL_FUNC(_kill)
	UNIMPL_FUNC(_wait)
	UNIMPL_FUNC(_times)
	UNIMPL_FUNC(_gettimeofday)
	UNIMPL_FUNC(_ftime)
	UNIMPL_FUNC(_utime)
	UNIMPL_FUNC(_chown)
	UNIMPL_FUNC(_chmod)
	UNIMPL_FUNC(_chdir)
	UNIMPL_FUNC(_getcwd)
	UNIMPL_FUNC(_sysconf)
	"j unimplemented_syscall\n"
);

void unimplemented_syscall()
{
	const char *p = "Unimplemented system call called!\n";
	while (*p)
		*(volatile int*)0x10000000 = *(p++);
	asm volatile ("ebreak");
	__builtin_unreachable();
}

ssize_t _read(int file, void *ptr, size_t len)
{
	// always EOF
	return 0;
}

ssize_t _write(int file, const void *ptr, size_t len)
{
	const void *eptr = ptr + len;
	while (ptr != eptr)
		*(volatile int*)0x10000000 = *(char*)(ptr++);
	return len;
}

int _close(int file)
{
	// close is called before _exit()
	return 0;
}

int _fstat(int file, struct stat *st)
{
	// fstat is called during libc startup
	errno = ENOENT;
	return -1;
}

void *_sbrk(ptrdiff_t incr)
{
	extern unsigned char _end[];   // Defined by linker
	static unsigned long heap_end;

	if (heap_end == 0)
		heap_end = (long)_end;

	heap_end += incr;
	return (void *)(heap_end - incr);
}

void _exit(int exit_status)
{
	asm volatile ("ebreak");
	__builtin_unreachable();
}