arno/linux-insides
1
0
Fork 0
mirror of https://github.com/0xAX/linux-insides.git synced 2024-12-22 22:58:08 +00:00
Code Issues Releases Wiki Activity

Fix typos

Browse Source
This commit is contained in:
Yaroslav Pronin 2019-07-14 17:49:36 +00:00 committed by GitHub
parent 1e017f37ad
commit b0e971f17d
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
Initialization/linux-initialization-4.md
View File

@ -68,7 +68,7 @@ union thread_union {
}; };
``` ```
Every process has its own stack and it is 16 kilobytes or 4 page frames. in `x86_64`. We can note that it is defined as array of `unsigned long`. The next field of the `thread_union` is - `thread_info` defined as: Every process has its own stack and it is 16 kilobytes or 4 page frames in `x86_64`. We can note that it is defined as array of `unsigned long`. The next field of the `thread_union` is - `thread_info` defined as:
```C ```C
struct thread_info { struct thread_info {
@ -86,7 +86,7 @@ struct thread_info {
}; };
``` ```
and occupies 52 bytes. The `thread_info` structure contains architecture-specific information on the thread. We know that on `x86_64` the stack grows down and `thread_union.thread_info` is stored at the bottom of the stack in our case. So the process stack is 16 kilobytes and `thread_info` is at the bottom. The remaining thread_size will be `16 kilobytes - 62 bytes = 16332 bytes`. Note that `thread_union` represented as the [union](http://en.wikipedia.org/wiki/Union_type) and not structure, it means that `thread_info` and stack share the memory space. and occupies 52 bytes. The `thread_info` structure contains architecture-specific information on the thread. We know that on `x86_64` the stack grows down and `thread_union.thread_info` is stored at the bottom of the stack in our case. So the process stack is 16 kilobytes and `thread_info` is at the bottom. The remaining thread size will be `16 kilobytes - 62 bytes = 16332 bytes`. Note that `thread_union` represented as the [union](http://en.wikipedia.org/wiki/Union_type) and not structure, it means that `thread_info` and stack share the memory space.
Schematically it can be represented as follows: Schematically it can be represented as follows:
@ -173,7 +173,7 @@ static inline unsigned long *end_of_stack(const struct task_struct *task)
#endif #endif
``` ```
As we got the end of the init process stack, we write `STACK_END_MAGIC` there. After `canary` is set, we can check it like this: As we got the end of the `init` process stack, we write `STACK_END_MAGIC` there. After `canary` is set, we can check it like this:
```C ```C
if (*end_of_stack(task) != STACK_END_MAGIC) { if (*end_of_stack(task) != STACK_END_MAGIC) {
@ -195,7 +195,7 @@ as it not implemented for all architectures, but some such as [s390](http://en.w
The next function in `start_kernel` is `debug_objects_early_init`. Implementation of this function is almost the same as `lockdep_init`, but fills hashes for object debugging. As I wrote above, we will not see the explanation of this and other functions which are for debugging purposes in this chapter. The next function in `start_kernel` is `debug_objects_early_init`. Implementation of this function is almost the same as `lockdep_init`, but fills hashes for object debugging. As I wrote above, we will not see the explanation of this and other functions which are for debugging purposes in this chapter.
After the `debug_object_early_init` function we can see the call of the `boot_init_stack_canary` function which fills `task_struct->canary` with the canary value for the `-fstack-protector` gcc feature. This function depends on the `CONFIG_CC_STACKPROTECTOR` configuration option and if this option is disabled, `boot_init_stack_canary` does nothing, otherwise it generates random numbers based on random pool and the [TSC](http://en.wikipedia.org/wiki/Time_Stamp_Counter): After the `debug_object_early_init` function we can see the call of the `boot_init_stack_canary` function which fills `task_struct->canary` with the `canary` value for the `-fstack-protector` gcc feature. This function depends on the `CONFIG_CC_STACKPROTECTOR` configuration option and if this option is disabled, `boot_init_stack_canary` does nothing, otherwise it generates random numbers based on random pool and the [TSC](http://en.wikipedia.org/wiki/Time_Stamp_Counter):
```C ```C
get_random_bytes(&canary, sizeof(canary)); get_random_bytes(&canary, sizeof(canary));
@ -215,7 +215,7 @@ and write this value to the top of the IRQ stack with the:
this_cpu_write(irq_stack_union.stack_canary, canary); // read below about this_cpu_write this_cpu_write(irq_stack_union.stack_canary, canary); // read below about this_cpu_write
``` ```
Again, we will not dive into details here, we will cover it in the part about [IRQs](http://en.wikipedia.org/wiki/Interrupt_request_%28PC_architecture%29). As canary is set, we disable local and early boot IRQs and register the bootstrap CPU in the CPU maps. We disable local IRQs (interrupts for current CPU) with the `local_irq_disable` macro which expands to the call of the `arch_local_irq_disable` function from [include/linux/percpu-defs.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/include/linux/percpu-defs.h): Again, we will not dive into details here, we will cover it in the part about [IRQs](http://en.wikipedia.org/wiki/Interrupt_request_%28PC_architecture%29). As `canary` is set, we disable local and early boot IRQs and register the bootstrap CPU in the CPU maps. We disable local IRQs (interrupts for current CPU) with the `local_irq_disable` macro which expands to the call of the `arch_local_irq_disable` function from [include/linux/percpu-defs.h](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/include/linux/percpu-defs.h):
```C ```C
static inline notrace void arch_local_irq_disable(void) static inline notrace void arch_local_irq_disable(void)