Anything that matters has / will be moved to: https://github.com/cirosantilli/linux-kernel-module-cheatt
This does not need to compile anymore.
- Code
- Introduction
- Build
- Use built kernel
- Source tree
- Testing
- Module
- Virtual address space
- Scheduling
- Virtualization
- Debug
- Style guide
- Trivia
WIP
User programs such as a simple hello world run inside an abstraction called process defined by the kernel.
The kernel restricts what user programs can do directly basically to basic processor operations (adding) and memory operations (setting or getting RAM memory).
User programs can, however, ask the kernel to do certain operations for them via system calls.
A simple example is the C printf function, which must at some point ask the kernel to print to stdout, probably via the write system call.
Another simple example is file IO.
uname -r
Sample output:
3.13.0-48-generic
TODO what does generic mean?
Or parse:
cat /proc/version
Sample output:
Linux version 3.13.0-48-generic (buildd@orlo) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #80-Ubuntu SMP Thu Mar 12 11:16:15 UTC 2015
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user space process can be interrupted by anything, including other user space processes.
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kernel space processes can be interrupted by other kernel processes or interrupts handlers, but not by user space processes.
Examples of things that generate kernel space processes:
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system calls
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module insertion/removal
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scheduled kernel processes such as softirqs.
those are run in kernel threads
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interrupt handlers cannot be interrupted by anything else, not even other interrupt handlers.
This section discusses issues specific to the x86 Linux implementation.
Intel reserves interrupt numbers from 0 to 31 for exceptions: anormal execution of instructions such as division by zero, or accessing forbidden memory areas.
Certain interrupt numbers are processor interrupts called exceptions.
Linux deals with those interrupts in interrupt handlers, and then if a user process generates one of those exceptions, the process is notified via a predefined signal.
0 Divide error SIGFPE
1 Debug SIGTRAP
2 NMI None
3 Breakpoint SIGTRAP
4 Overflow SIGSEGV
5 Bounds check SIGSEGV
6 Invalid opcode SIGILL
7 Device not available None
8 Double fault None
9 Coprocessor segment overrun SIGFPE
10 Invalid TSS SIGSEGV
11 Segment not present SIGBUS
12 Stack segment fault SIGBUS
13 General protection SIGSEGV
14 Page Fault SIGSEGV
15 Intel-reserved None
16 Floating-point error SIGFPE
17 Alignment check SIGBUS
18 Machine check None
19 SIMD floating point SIGFPE