Input / Output Flashcards
1
Q
How does a program running in EL0 do I/O?
A
It makes a system call, generating an exception by using the svc instruction, with the request value in x8
2
Q
(T/F) All peripheral devices are represented as file
A
True
3
Q
What are the service requests and their corresponding values?
A
openat - 56
close - 57
read - 63
write - 64
4
Q
Where is the return value of a system call stored?
A
In x0
5
Q
What is the C function to open a file?
A
openat(int dirfd, const char *pathname, int flags, mode_t mode);
6
Q
What is the C function to read from a file?
A
read(int fd, void *buf, unsigned long n);
7
Q
What is the C function to write to a file?
A
write(int fd, void* buf, unsigned long n);
8
Q
How is the buffer base calcultated?
A
add buf_base, x29, buf_s
9
Q
What is the value of AT_FDCWD?
A
-100
