Use the same idea, where the type of a ?: expression depends on whether an argument is a null pointer constant or an ordinary void *, but detect the type with _Generic: #define ICE_P(x) _Generic((1? (void *) ((x)*0) : (int *) 0), int*: 1, void*: 0) Demo on Ideone. _Generic is a C11 addition, so … Read more
Best moments of the exec system call on Linux 4.0 The best way to find all of that out is to GDB step debug the kernel with QEMU: How to debug the Linux kernel with GDB and QEMU? fs/exec.c defines the system call at SYSCALL_DEFINE3(execve Simply forwards to do_execve. do_execve Forwards to do_execveat_common. do_execveat_common To … Read more
Based on recent libcap2 update 1: (Short option): getpcaps Description: From here: getpcaps displays the capabilities on the processes indicated by the pid value(s) given on the command line. Example: $ getpcaps <PID> PID: = cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap+i 2: (A bit longer option): /proc status and capsh Description: proc is a process information pseudo-filesystem or in other … Read more
spin_lock_irqsave is basically used to save the interrupt state before taking the spin lock, this is because spin lock disables the interrupt, when the lock is taken in interrupt context, and re-enables it when while unlocking. The interrupt state is saved so that it should reinstate the interrupts again. Example: Lets say interrupt x was … Read more
You’ll need the Linux kernel sources in order to see the actual source of the system calls. Manual pages, if installed on your local system, only contain the documentation of the calls and not their source itself. Unfortunately for you, system calls aren’t stored in just one particular location in the whole kernel tree. This … Read more
The linux/version.h file has a macro called KERNEL_VERSION which will let you check the version you want against the current linux headers version (LINUX_VERSION_CODE) installed. For example to check if the current Linux headers are for kernel v2.6.16 or earlier: #include <linux/version.h> #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,16) … #else … #endif A better way to get … Read more
I needed to include <linux/delay.h> to use msleep in kernel space.
This is an optimization done by linux/glibc to make futexes faster when they’re not shared between processes. Glibc will use the _PRIVATE versions of each of the futex calls unless the PTHREAD_PROCESS_SHARED attribute is set on your mutex It’s explained in more detail here: http://lwn.net/Articles/229668/ For the purposes of your debugging, you can just ignore … Read more
While the proc manpage is woefully behind (and so are most manpages/documentation on anything not relating to cookie-cutter user-space development), this stuff is fortunately documented completely in the Linux kernel source under Documentation/filesystems/proc.rst. Here are the relevant bits: rchar —– I/O counter: chars read The number of bytes which this task has caused to be … Read more
My answer is true for Intel CPUs running on a modern Linux system, and I am speaking about user-level processes, not kernel code. Still, I think it’ll give you some insight enough to think about the other possibilities Address Types Regarding question 3: I have come across discussion that virtual and logical addresses/address space are … Read more