newlib-cygwin/libgloss/riscv/sys_read.c

#include <machine/syscall.h>
#include <sys/types.h>
#include "internal_syscall.h"

/* Read from a file.  */
ssize_t _read(int file, void *ptr, size_t len)
{
  return syscall_errno (SYS_read, 3, file, ptr, len, 0, 0, 0);
}
RISC-V: Moved syscalls to separate files to fix aliasing problems. 2017-12-27 04:27:52 +08:00			`#include <machine/syscall.h>`
			`#include <sys/types.h>`
			`#include "internal_syscall.h"`

			`/* Read from a file. */`
			`ssize_t _read(int file, void *ptr, size_t len)`
			`{`
Only pass the minimum number of syscall arguments Previously, __internal_syscall() compiled into asm-code that unconditionally sets the syscall argument registers a0 to a5. For example, the instruction sequence for a exit syscall looked like this: li a0, 1 # in ther caller of exit() # ... # in newlib: li a1, 0 # unused arguments li a2, 0 li a3, 0 li a4, 0 li a5, 0 li a7, 93 # exit syscall number (i.e. the binary contains then 5 superfluous instructions for this one argument syscall) This commit changes the RISC-V syscall code such that only the required syscall argument registers are set. GCC detects that argc is known at compile time and thus evaluates all the if-statements where argc is used at compile time (tested with -O2 and -Os). 2020-02-11 04:19:58 +08:00			`return syscall_errno (SYS_read, 3, file, ptr, len, 0, 0, 0);`
RISC-V: Moved syscalls to separate files to fix aliasing problems. 2017-12-27 04:27:52 +08:00			`}`