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Merge pull request #310 from spacewander/linux-interrupts-2-fix

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fix typo from interrupts-2
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0xAX 2016-01-08 14:50:24 +06:00
commit bb83b77412
1 changed files with 5 additions and 5 deletions
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10
interrupts/interrupts-2.md
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@ -129,7 +129,7 @@ We pass `irq_stack_union` symbol to the `INIT_PER_CPU_VAR` macro which just conc
INIT_PER_CPU(irq_stack_union);
```
It tells us that the address of the `init_per_cpu__irq_stack_union` will be `irq_stack_union + __per_cpu_load`. Now we need to understand where `init_per_cpu__irq_stack_union` and `__per_cpu_load` are and what they mean. The first `irq_stack_union` is defined in the [arch/x86/include/asm/processor.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/processor.h) with the `DECLARE_INIT_PER_CPU` macro which expands to call the `init_per_cpu_var` macro:
It tells us that the address of the `init_per_cpu__irq_stack_union` will be `irq_stack_union + __per_cpu_load`. Now we need to understand where `init_per_cpu__irq_stack_union` and `__per_cpu_load` are what they mean. The first `irq_stack_union` is defined in the [arch/x86/include/asm/processor.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/processor.h) with the `DECLARE_INIT_PER_CPU` macro which expands to call the `init_per_cpu_var` macro:
```C
DECLARE_INIT_PER_CPU(irq_stack_union);
@ -266,7 +266,7 @@ union irq_stack_union {
};
```
which defined in the [arch/x86/include/asm/processor.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/processor.h). We know that [unioun](http://en.wikipedia.org/wiki/Union_type) in the [C](http://en.wikipedia.org/wiki/C_%28programming_language%29) programming language is a data structure which stores only one field in a memory. We can see here that structure has first field - `gs_base` which is 40 bytes size and represents bottom of the `irq_stack`. So, after this our check with the `BUILD_BUG_ON` macro should end successfully. (you can read the first part about Linux kernel initialization [process](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-1.html) if you're interesting about the `BUILD_BUG_ON` macro).
which defined in the [arch/x86/include/asm/processor.h](https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/processor.h). We know that [union](http://en.wikipedia.org/wiki/Union_type) in the [C](http://en.wikipedia.org/wiki/C_%28programming_language%29) programming language is a data structure which stores only one field in a memory. We can see here that structure has first field - `gs_base` which is 40 bytes size and represents bottom of the `irq_stack`. So, after this our check with the `BUILD_BUG_ON` macro should end successfully. (you can read the first part about Linux kernel initialization [process](http://0xax.gitbooks.io/linux-insides/content/Initialization/linux-initialization-1.html) if you're interesting about the `BUILD_BUG_ON` macro).
After this we calculate new `canary` value based on the random number and [Time Stamp Counter](http://en.wikipedia.org/wiki/Time_Stamp_Counter):
@ -304,7 +304,7 @@ This macro defined in the [include/linux/irqflags.h](https://github.com/torvalds
#endif
```
They are both similar and as you can see have only one difference: the `local_irq_disable` macro contains call of the `trace_hardirqs_off` when `CONFIG_TRACE_IRQFLAGS_SUPPORT` is enabled. There is special feature in the [lockdep](http://lwn.net/Articles/321663/) subsystem - `irq-flags tracing` for tracing `hardirq` and `stoftirq` state. In ourcase `lockdep` subsytem can give us interesting information about hard/soft irqs on/off events which are occurs in the system. The `trace_hardirqs_off` function defined in the [kernel/locking/lockdep.c](https://github.com/torvalds/linux/blob/master/kernel/locking/lockdep.c):
They are both similar and as you can see have only one difference: the `local_irq_disable` macro contains call of the `trace_hardirqs_off` when `CONFIG_TRACE_IRQFLAGS_SUPPORT` is enabled. There is special feature in the [lockdep](http://lwn.net/Articles/321663/) subsystem - `irq-flags tracing` for tracing `hardirq` and `stoftirq` state. In our case `lockdep` subsytem can give us interesting information about hard/soft irqs on/off events which are occurs in the system. The `trace_hardirqs_off` function defined in the [kernel/locking/lockdep.c](https://github.com/torvalds/linux/blob/master/kernel/locking/lockdep.c):
```C
void trace_hardirqs_off(void)
@ -314,7 +314,7 @@ void trace_hardirqs_off(void)
EXPORT_SYMBOL(trace_hardirqs_off);
```
and just calls `trace_hardirqs_off_caller` function. The `trace_hardirqs_off_caller` checks the `hardirqs_enabled` filed of the current process increment the `redundant_hardirqs_off` if call of the `local_irq_disable` was redundant or the `hardirqs_off_events` if it was not. These two fields and other `lockdep` statistic related fields are defined in the [kernel/locking/lockdep_insides.h](https://github.com/torvalds/linux/blob/master/kernel/locking/lockdep_insides.h) and located in the `lockdep_stats` structure:
and just calls `trace_hardirqs_off_caller` function. The `trace_hardirqs_off_caller` checks the `hardirqs_enabled` field of the current process and increases the `redundant_hardirqs_off` if call of the `local_irq_disable` was redundant or the `hardirqs_off_events` if it was not. These two fields and other `lockdep` statistic related fields are defined in the [kernel/locking/lockdep_insides.h](https://github.com/torvalds/linux/blob/master/kernel/locking/lockdep_insides.h) and located in the `lockdep_stats` structure:
```C
struct lockdep_stats {
@ -371,7 +371,7 @@ static inline void native_irq_disable(void)
}
```
And you already must remember that `cli` instruction clears the [IF](http://en.wikipedia.org/wiki/Interrupt_flag) flag which determines ability of a processor to handle and interrupt or an exception. Besides the `local_irq_disable`, as you already can know there is an inverse macr - `local_irq_enable`. This macro has the same tracing mechanism and very similar on the `local_irq_enable`, but as you can understand from its name, it enables interrupts with the `sti` instruction:
And you already must remember that `cli` instruction clears the [IF](http://en.wikipedia.org/wiki/Interrupt_flag) flag which determines ability of a processor to handle an interrupt or an exception. Besides the `local_irq_disable`, as you already can know there is an inverse macro - `local_irq_enable`. This macro has the same tracing mechanism and very similar on the `local_irq_enable`, but as you can understand from its name, it enables interrupts with the `sti` instruction:
```C
static inline void native_irq_enable(void)