systems-programming

I'm writing system-level code for an embedded system without memory protection (on an ARM Cortex-M1, compiling with gcc 4.3) and need to read/write directly to a memory-mapped register. So far, my code looks like this: #define UART0 0x4000C000 #define UART0CTL (UART0 + 0x30) volatile unsigned int *p; p = UART0CTL; *p &= ~1; Is there any shorter way (shorter in code, I mean) that does not use a pointer? I looking for a way to write the actual assignment code as short as this (it would be okay if I had to use more #defines): *(UART0CTL) &= ~1; Anything I tried so far ended up with gcc

I was doing a little reading about sigaction() (sources are from my course notes) and I'm not sure I understand this text: The signal mask is calculated and installed only for the duration of the signal handler. By default, the signal “sig” is also blocked when the signal occurs. Once an action is installed for a specific signal using sigaction, it remains installed until another action is explicitly requested. Does this mean that the default signal mask is restored after returning form the signal handler? Also, do I have to re-install the handler after using it, as if I was using signal() ?

I have a file containing command lines that I want to run. This file contains around 2,000 lines. I have 8 cores available. Is it possible to parse the file and start 8 processes, then execute another one from the file whenever one of the programs finishes? I want this to continue until the end of file is reached. You can use xargs to read in the file, while limiting the maximum number of processes to the number of available cores. For example: cores=$(fgrep -c processor /proc/cpuinfo) xargs --arg-file=/tmp/foo \ --max-procs=$cores \ --replace \ --verbose \ /bin/sh -c "{}" Use GNU parallel .

Considering the below code : int main() { int pid; pid=vfork(); if(pid==0) printf("child\n"); else printf("parent\n"); return 0; } In case of vfork() the adress space used by parent process and child process is same, so single copy of variable pid should be there. Now i cant understand how this pid variable can have two values returned by vfork() i.e. zero for child and non zero for parent ? In case of fork() the adress space also gets copied and there are two copy of pid variable in each child and parent, so I can understand in this case two different copies can have different values returned

Compiler: clang++ x86-64 on linux. It has been a while since I have written any intricate low level system code, and I ussualy program against the system primitives (windows and pthreads/posix). So, the in#s and out's have slipped from my memory. I am working with boost::asio and boost::thread at the moment. In order to emulate synchronous RPC against an asynchronous function executor ( boost::io_service with multiple threads io::service::run 'ing where requests are io_serviced::post 'ed), I am using boost synchronization primitives. For curiosities sake I decided to sizeof the primitives.