strace/linux/x86_64/get_syscall_args.c

/* Return -1 on error or 1 on success (never 0!). */
static int
get_syscall_args(struct tcb *tcp)
{
	if (x86_io.iov_len != sizeof(i386_regs)) {
		/* x86-64 or x32 ABI */
		tcp->u_arg[0] = x86_64_regs.rdi;
		tcp->u_arg[1] = x86_64_regs.rsi;
		tcp->u_arg[2] = x86_64_regs.rdx;
		tcp->u_arg[3] = x86_64_regs.r10;
		tcp->u_arg[4] = x86_64_regs.r8;
		tcp->u_arg[5] = x86_64_regs.r9;
#ifdef X32
		tcp->ext_arg[0] = x86_64_regs.rdi;
		tcp->ext_arg[1] = x86_64_regs.rsi;
		tcp->ext_arg[2] = x86_64_regs.rdx;
		tcp->ext_arg[3] = x86_64_regs.r10;
		tcp->ext_arg[4] = x86_64_regs.r8;
		tcp->ext_arg[5] = x86_64_regs.r9;
#endif
	} else {
		/* i386 ABI */
		/* Zero-extend from 32 bits */
		/* Use widen_to_long(tcp->u_arg[N]) in syscall handlers
		 * if you need to use *sign-extended* parameter.
		 */
		tcp->u_arg[0] = (long)(uint32_t)i386_regs.ebx;
		tcp->u_arg[1] = (long)(uint32_t)i386_regs.ecx;
		tcp->u_arg[2] = (long)(uint32_t)i386_regs.edx;
		tcp->u_arg[3] = (long)(uint32_t)i386_regs.esi;
		tcp->u_arg[4] = (long)(uint32_t)i386_regs.edi;
		tcp->u_arg[5] = (long)(uint32_t)i386_regs.ebp;
	}
	return 1;
}