A system call is used by programs to request services from the operating system's kernel.
Questions tagged [system-calls]
3690 questions
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1 answer
why setuid fails after capset is used?
trying to figure out the linux capabilities interface, i came across with an unexpected issue (for me at least). When seting the capabilities of a process with the capset syscall the kernel rejects a change of userid with the setuid syscall. Does…
Lino Bossio
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filesystem fd from file fd
My program opens a file and wants to set O_DIRECT for it. But the program assumes block size of 512. So, I need to check for that size. man 2 open suggests to do it like this ioctl(filesystem_fd, BLKSSZGET, &block_size).
And my question is: how to…
Eugene Kosov
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2 answers
What are the __NR_-prefixed symbols in glibc?
I'm trying to compile Box86 on Alpine Linux, a Linux distribution which uses the musl libc implementation rather than glibc. At 46% completion, the compilation halts with the following errors:
/home/newbyte/box86/src/emu/x86syscall.c:124:11: error:…
Newbyte
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1 answer
C syscall() cannot accept void pointers
I am working on a dynamic language written in go. I am using C to allow this language to access syscalls (for linux at least). C's any type is a void*, so I thought that I can pass them into a syscall. I tested using some code which looks…
Ank i zle
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1 answer
Performing syscalls in inline C assembly causes a segfault
I recently dabbled into low level programming, and want to make a function somesyscall that accepts (CType rax, CType rbx, CType rcx, CType rdx). struct CType looks like:
/*
TYPES:
0 int
1 string
2 bool
*/
typedef struct…
Ank i zle
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0 answers
Socket C - Address family not supported by protocol
So I am trying to create a packet sniffer in C. After following the man7 page I inferred that the socket function should look like this
.....
int socketfd = socket(AF_PACKET , SOCK_RAW , htons(ETH_P_ALL));
if(socketfd < 0)
{
perror("Socket…
Patch
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why Packets are not received via raw socket from all protocol using ETH_P_ALL?
package main
import (
"fmt"
"syscall"
)
func main() { `
fd, err:= syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, syscall.ETH_P_ALL) //opening raw socket
if (err != nil) {
fmt.Println("Error: " + err.Error())
return;
}
…
nivetha a
- 11
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1 answer
Error when copying data from kernel to user space using copy_to_user()
#include
#include
unsigned long long cnt = 0;
asmlinkage long sys_customcall(unsigned long long __user *output)
{
unsigned long err;
err = copy_to_user(output, &cnt, sizeof(unsigned long…
SY LEE
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Meaning of 'vector' in asm context
For something like:
int $0x80
I understand that it is executing the int instruction on the destination operand value 0x80 or 128. And, if I'm understanding correctly, 128 is a system call and it'll execute the call that is stored in eax. However,…
samuelbrody1249
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1 answer
Search for bad sectors of a device in C
I'm trying to create a simple script in c which is able to identify bad sectors of (a device) for educational purpose. In my example, I use an HD with read-only mode. The idea behind is simple, but maybe too simple and I would know if this is…
Virgula
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Remote mmap syscall using ptrace (Linux, C)
I've been stuck with this problem for some days, and still haven't manage to fix it. Basically, I want to do a remote syscall from an attacker program to the target. But before showing the code, I think it'd be a good idea to present my thought…
rdbo
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2 answers
Why doesn't readlink return a null-terminated value?
Both The Single UNIX ® Specification, Version 2 (1997) and The Open Group Base Specifications Issue 6 (2004) require that readlink would not place a null-terminated value in buffer:
APPLICATION USAGE
Conforming applications should not assume that…
Yam Mesicka
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replacing system() with execl() : when do I need to use fork()?
I am trying to call an external program from within my C program. I understand that calling system() is a bad habit. I've been reading up on how to use execl() or execv() to replace system(), but due to my limited brain capacity, I would like to…
kwantum
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3 answers
My ifstream doesn't seem to be working
This is a main file that I am using to test methods before I implement them. I am trying to get the list of all files in a directory, write them to a txt file (It works fine until here), then read the file names from that text file.
using namespace…
mrswmmr
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1 answer
Understanding how waitpid works with signals
Consider the following Pseudo-C code:
static int G = 0;
void alrm_handler(int signo) {
G = 1;
}
void son() {
struct sched_param param;
param.sched_priority = 50;
sched_setscheduler(getpid(),SCHED_FIFO, ¶m);
kill(getppid(),…
vesii
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