system-calls

I'm having a go at writing a very light weight libc replacement library so that I can better understand the kernel - application interface. The first task is clearly getting some system call wrappers in place. I've successfully got 1 to 3 argument wrappers working but I'm struggling with a 4 argument varient. Here's my starting point: long _syscall4(long type, long a1, long a2, long a3, long a4) { long ret; asm ( "syscall" : "=a"(ret) : "a"(type), "D"(a1), "S"(a2), "d"(a3), "r10"(a4) : "c", "r11" ); return ret; } The compiler gives me the following error: error: matching constraint references

Short version of question: What parameter do I need to pass to the clone system call on x86_64 Linux system if I want to allocate a new TLS area for the thread that I am creating. Long version : I am working on a research project and for something I am experimenting with I want to create threads using the clone system call instead of using pthread_create . However, I also want to be able to use thread local storage. I don't plan on creating many threads right now, so it would be fine for me to create a new TLS area for each thread that I create with the clone system call. I was looking at the

To simulate some behavior I would like to attach a probe to a syscall and modify the return value when certain parameters are passed. Alternatively, it would also be enough to modify the parameters of the function before they are processes. Is this possible with BPF? I believe that attaching eBPF to kprobes/kretprobes gives you read access to function arguments and return values, but that you cannot tamper with them. I am NOT 100% sure; good places to ask for confirmation would be the IO Visor project mailing list or IRC channel (#iovisor at irc.oftc.net). As an alternative solution, I know

How to iterate through all tids of all threads of the current process? Is there some way that doesn't involve diving into /proc ? lvella The code I am using, based on reading /proc #include <sys/types.h> #include <dirent.h> #include <stdlib.h> #include <stdio.h> Then, from inside a funcion: DIR *proc_dir; { char dirname[100]; snprintf(dirname, sizeof dirname, "/proc/%d/task", getpid()); proc_dir = opendir(dirname); } if (proc_dir) { /* /proc available, iterate through tasks... */ struct dirent *entry; while ((entry = readdir(proc_dir)) != NULL) { if(entry->d_name[0] == '.') continue; int tid =