在 2008-06-05四的 15:32 +0530，Chetan Nanda写道： > Hi All, > I was reading the boot code for MIPS. > in head.S file before jumping to 'start_kernel' it calculate the stack > pointer address as follow: > > " > PTR_LA $28, init_thread_union > PTR_ADDIU sp, $28, _THREAD_SIZE - 32 make sp point to the stack top so that we can allocate stack space later, -32 is a reserved area for local variable, saved GPR, arguments (function stack frame).. due to the abi > set_saved_sp sp, t0, t1 set_saved_sp is defined (as a assembler macro) in include/asm-mips/stackframe.h (if you're using vim, I think it will be easy to use vim with cscope..) > PTR_SUBU sp, 4 * SZREG # init stack pointer SZREG is defined to the general purpose register size, it is 32bit in MIPS32 and 64bit in MIPS64, so the last line allocates 16/32 bytes to build a stack frame.. You could refer to the MIPS ABI if you need further information (the kernel don't follow the standard ABI all the time though..) > > Can anyone please explains me this 4 lines of code? > Why ' _THREAD_SIZE - 32' is added in 'sp' ? > What 'set_saved_sp' will do ? > and then why we subtract '4 * SZREG' from 'sp' ? > > Please hep me to understand this code better. > > Thanks, > Chetan Nanda > -- Wang, Baojun Lanzhou University Distributed & Embedded System Lab http://dslab.lzu.edu.cn School of Information Science and Engeneering wangbj@xxxxxxxxxxxxxxxx Tianshui South Road 222. Lanzhou 730000 .P.R.China Tel: +86-931-8912025 Fax: +86-931-8912022
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