sysinfo
This program displays information about the local system. In particular, it shows CPU load average from /proc/loadavg and memory usage from /proc/meminfo.
This program demonstates the use of inline assembly and system calls. It will not #include or link against any external files. It does not use the C standard library.
Your task is to properly implement the open and read system calls and use them to implement the program. Examples have been provided for the write and exit system calls. Because this lab directly uses x64 Linux system calls, it must be completed in an x64 Linux environment.
Expected Output
The completed program will produce output that looks approximately like the following:
sysinfo 1.0
Load Average
0.24 0.45 0.52 3/1107 702033
Memory Usage
MemTotal: 32202816 kB
MemFree: 6661620 kB
MemAvailable: 19755544 kB
Buffers: 1536760 kB
Cached: 11621876 kB
SwapCached: 0 kB
Active: 16603636 kB
Inactive: 6919156 kB
Active(anon): 10898016 kB
Inactive(anon): 88672 kB
Active(file): 5705620 kB
Inactive(file): 6830484 kB
Unevictable: 534808 kB
Mlocked: 16 kB
SwapTotal: 2097148 kB
SwapFree: 2097148 kB
Dirty: 136 kB
Writeback: 0 kB
AnonPages: 10899012 kB
Mapped: 664072 kB
Shmem: 627672 kB
KReclaimable: 1023236 kB
Slab: 1303804 kB
SReclaimable: 1023236 kB
SUnreclaim: 280568 kB
KernelStack: 17856 kB
PageTables: 47600 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 18198556 kB
Committed_AS: 14965320 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 49232 kB
VmallocChunk: 0 kB
Percpu: 21120 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
FileHugePages: 0 kB
FilePmdMapped: 0 kB
CmaTotal: 0 kB
CmaFree: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 0 kB
DirectMap4k: 775088 kB
DirectMap2M: 18458624 kB
DirectMap1G: 14680064 kB
Example C Program
The following example program that will output the first 4096 bytes of the file /proc/loadavg may be useful example of the open, read, and write system calls in action:
#include <unistd.h>
#include <fcntl.h>
int main() {
char buf[4096];
int fd = open("/proc/loadavg", O_RDONLY);
int bytes_read = read(fd, buf, 4096);
write(STDOUT_FILENO, buf, bytes_read);
}The example implementation of write and exit may also be informative.
Documentation
The register names by GCC can be a little opaque due to the way the x86 system has evolved. Here are the common ones:
| name | description |
|---|---|
| a | The rax register. |
| b | The rbx register. |
| c | The rcx register. |
| d | The rdx register. |
| S | The rsi register. |
| D | The rdi register. |
Here are some key notes extracted from the kernel calling convention documentation (Section A.2):
- User-level applications use as integer registers for passing the sequence %rdi, %rsi, %rdx, %rcx, %r8 and %r9. The kernel interface uses %rdi, %rsi, %rdx, %r10, %r8 and %r9.
- A system-call is done via the syscall instruction. The kernel destroys registers %rcx and %r11.
- The number of the syscall has to be passed in register %rax.
- System-calls are limited to six arguments, no argument is passed directly on the stack.
- Returning from the syscall, register %rax contains the result of the system-call. A value in the range between -4095 and -1 indicates an error, it is -errno.
The following may also be helpful.