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Questions tagged [system-calls]

A system call is used by programs to request services from the operating system's kernel.

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How is malloc() implemented internally?

Can anyone explain how malloc() works internally? I have sometimes done strace program and I see a lot of sbrk system calls, doing man sbrk talks about it being used in malloc() but not much more.
bodacydo
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What does "int 0x80" mean in assembly code?

Can someone explain what the following assembly code does? int 0x80
Josh Curren
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dup2 / dup - Why would I need to duplicate a file descriptor?

I'm trying to understand the use of dup2 and dup. From the man page: DESCRIPTION dup and dup2 create a copy of the file descriptor oldfd. After successful return of dup or dup2, the old and new descriptors may be used interchangeably. They share…
JAN
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Magic numbers of the Linux reboot() system call

The Linux Programming Interface has an exercise in Chapter 3 that goes like this: When using the Linux-specific reboot() system call to reboot the system, the second argument, magic2, must be specified as one of a set of magic numbers…
Wei Hu
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How to write a signal handler to catch SIGSEGV?

I want to write a signal handler to catch SIGSEGV. I protect a block of memory for read or write using char *buffer; char *p; char a; int pagesize = 4096; mprotect(buffer,pagesize,PROT_NONE) This protects pagesize bytes of memory starting at…
Adi
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What is better "int 0x80" or "syscall" in 32-bit code on Linux?

I study the Linux kernel and found out that for x86_64 architecture the interrupt int 0x80 doesn't work for calling system calls1. For the i386 architecture (32-bit x86 user-space), what is more preferable: syscall or int 0x80 and why? I use Linux…
Alex
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practical examples use dup or dup2

I know what dup / dup2 does, but I have no idea when it would be used. Any practical examples? Thanks.
pierrotlefou
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What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code?

int 0x80 on Linux always invokes the 32-bit ABI, regardless of what mode it's called from: args in ebx, ecx, ... and syscall numbers from /usr/include/asm/unistd_32.h. (Or crashes on 64-bit kernels compiled without CONFIG_IA32_EMULATION). 64-bit…
Peter Cordes
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How to control which core a process runs on?

I can understand how one can write a program that uses multiple processes or threads: fork() a new process and use IPC, or create multiple threads and use those sorts of communication mechanisms. I also understand context switching. That is, with…
poundifdef
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System call and context switch

I am sorry to ask this question when it has already been asked but I couldn't get a clarity from them. So I am asking the following related questions to get the difference between system call (mode-switch) and context switch Why is it said that…
vjain27
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Is it true that fork() calls clone() internally?

I read in the 3rd chapter of the "Linux Kernel Development, Second Edition" by Robert Love (ISBN:0-672-32720-1) that the clone system call is used to create a thread in Linux. Now the syntax of clone is such that a starting routine/function address…
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What is the difference between the functions of the exec family of system calls like exec and execve?

I have been following a system programming course recently and I came through the system calls exec() and execve(). So far I cannot find any difference between these two, Even the Wikipedia does not give a clear explanation, so is there a…
buddhi weerasinghe
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warning: incompatible implicit declaration of built-in function ‘printf’ [enabled by default]

I'm using the following C code: #include #include #include int main() { int file=0; if((file=open("testfile.txt",O_RDONLY)) < -1) return 1; char buffer[19]; if(read(file,buffer,19) !=…
user3000926
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How do I get a thread ID from an arbitrary pthread_t?

I have a pthread_t, and I'd like to change its CPU affinity. The problem is that I'm using glibc 2.3.2, which doesn't have pthread_setaffinity_np(). That's OK, though, because pthread_setaffinity_np() is itself a wrapper of sched_setaffinity(),…
Skrud
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How do system calls work?

I understand that a user can own a process and each process has an address space (which contains valid memory locations, this process can reference). I know that a process can call a system call and pass parameters to it, just like any other library…
xyz
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