2012-07-24

07/24: JuluOSDev 讀書會 : Lab 3 review & stm32 Ethernet overview

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ben6

kclin

Lab3 Sharing:

Discussion 1 = because JOS is single kernel thread so that don't need to add $4.%%esp after call trap.

JOS

env_pop_tf

movl %0,%%esp

xv6

_alltraps:

add $4, %%esp

== end discussion 1

Fast system call

inline assembly

you cannot use

lea IamBack, %ebp

...

IamBack:

use bellow instead (because compiler implement)

lea 0f, %ebp

....

%ebp cannot use as

reduce stack push number - syscall_trap

arch/x86/include/asm/stackprotector.h

* On x86_64, %gs is shared by percpu area and stack canary. All

* percpu symbols are zero based and %gs points to the base of percpu

* area. The first occupant of the percpu area is always

* irq_stack_union which contains stack_canary at offset 40. Userland

* %gs is always saved and restored on kernel entry and exit using

* swapgs, so stack protector doesn't add any complexity there.

* On x86_32, it's slightly more complicated. As in x86_64, %gs is

* used for userland TLS. Unfortunately, some processors are much

* slower at loading segment registers with different value when

* entering and leaving the kernel, so the kernel uses %fs for percpu

* area and manages %gs lazily so that %gs is switched only when

* necessary, usually during task switch.

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