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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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Is "asmlinkage" required for a c function to be called from assembly?

I am writing a C function that will be invoked from assembly code. (Specifically, I want to do some checking job in the path of system call handling in linux kernel, so I will call the c function before a system call is dispatched in entry_32.S) I…
Infinite
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x86_64 Assembly Linux System Call Confusion

I am currently learning Assembly language on Linux. I have been using the book 'Programming From the Ground Up' and all the examples are 32-bit. My OS is 64-bit and I have been trying to do all the examples in 64-bit. I am having trouble…
Hudson Worden
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How does a system call translate to CPU instructions?

Let's say there is a simple program like: #include void main() { int x; printf("Cool"); fd = open("/tmp/cool.txt", O_READONLY) } The open is a system call here. I suppose when the shell runs it, it makes some hundred other…
Nishant
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How to figure out if a file is a link?

I have the below code only a part of it is shown here and I am checking if a the type of file. struct stat *buf /* just to show the type buf is*/ switch (buf.st_mode & S_IFMT) { case S_IFBLK: printf(" block device\n"); break; …
Eternal Learner
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What is the difference between system call and library call?

Can someone explain the differences for these two in linux? Please go as deep as possible into each step the operating system takes.
drdot
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Is there a better way than parsing /proc/self/maps to figure out memory protection?

On Linux (or Solaris) is there a better way than hand parsing /proc/self/maps repeatedly to figure out whether or not you can read, write or execute whatever is stored at one or more addresses in memory? For instance, in Windows you have…
Edward Kmett
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How do SYSCALL/SYSRET instructions perform across x86 CPUs?

SYSCALL and SYSRET (and their 32-bit-only Intel counterparts SYSENTER and SYSEXIT) are usually described as a “generally faster” way to enter and exit supervisor mode in x86 processors than call gates or software interrupts, but the exact figures…
Alex Shpilkin
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How to pass arguments to processes created by fork()

I want to create copies of a process using fork() in C. I cant figure out how to pass arguments to the copies of my process. For example,I want to pass an integer to the process copies. Or I what to do, if I have a loop in which I call fork() and…
Basti
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Programmatically getting UID and GID from username in Unix?

I'm trying to use setuid() and setgid() to set the respective id's of a program to drop privileges down from root, but to use them I need to know the uid and gid of the user I want to change to. Is there a system call to do this? I don't want to…
Evan
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System calls overhead

I just started studying about system calls. I would like to know what causes overhead when a system call is made. For example, if we consider getpid(), when a system call is made to getpid() my guess is that if the control is…
user3344978
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poll system call timeout

Attaching strace shows a lot of these messages: poll([{fd=5, events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}, {fd=9, events=POLLIN}, {fd=10, events=POLLIN}], 6, 0) = 0 (Timeout) poll([{fd=5, events=POLLIN},…
mahmood
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compile errors using signal.h in Linux

I'm writing a shell program that must handle signals. My relevant signal handling related code is as follows: #include ... #include ... void installSigactions( int, struct sigaction* ); void handler_function( int signal_id…
rurouniwallace
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ptrace and threads

I'm working on an linux application incorporating ptrace to observe the threads of another process. When the application I observe forks a child process this already works quite well. By calling waitpid in my application I can obtain the following…
mupro
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How to hide command prompt window when using Exec in Golang?

say i have the following code, using syscall to hide command line window process := exec.Command(name, args...) process.SysProcAttr = &syscall.SysProcAttr{HideWindow: true} err := process.Start() if err != nil { log.Print(err) } but when i…
jm33_m0
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Windows equivalent to Linux's readahead syscall?

Is there a Windows equivalent to Linux's readahead syscall? EDIT: I would like a full function signature if possible, showing the equivalent offset/count parameters (or lower/upper). Eg: The Linux function signature is: ssize_t readahead(int fd,…
joemoe
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