Hi Hesham, Thanks for your reply. I get it.
Best Regards, Shijun
2017-05-31 11:45 GMT+08:00 Hesham.Almatary@data61.csiro.au:
Hi Shijun,
_sel4_start sets up the stack (for the root task) as libmusl expects, and then jumps to _start (from libmuscl) and *NOT* the one at sel4platsupport/crt0.S. The _start function you're after (called by _sel4_start) exists in libmuslc for each arch e.g. libmuslc/arch/arm/crt_arch.h.
Cheers, Hesham
On 31/05/17 12:59, shijun zhao wrote:
Hi,
I’m tracing the path where sel4 kernel jumps to an application, such as hello-1.
From the Makefile for apps I know that the entry of the hello-1.bin is */_sel4_start/* which is defined in the sel4_crt0.S (the directory is sel4_tutorials/projects/sel4_libs_libsel4platsupport/src/arch/arm). The */_sel4_start/* function first calls a C function called */sel4_InitBootInfo/*, and finally jumps to the */_start/* function which is defined in the crt0.S. However the */_start/* in crt0.S calls the sel4_InitBootInfo again. What confuses me is that the sel4_InitBootInfo function requires an input argument passed by R0, however the R0 has been set to zero in the _sel4_start function, so I think the calling of sel4_InitBootInfo in the _start will not run correctly.
Or is the path where the kernel jumps to the app (_sel4_start->_start->main) wrong?
I paste referred codes below:
*/******sel4_crt0.S********************/*
_sel4_start:
/* Setup a stack for ourselves. */ ldr sp, =_stack_top /* Setup bootinfo. The pointer to the bootinfo struct starts in'r0'. */
bl seL4_InitBootInfo ............ mov r0, #0 // *The R0 is modified, so it doesn't store thebootinfo structure anymore!*
............ /* Now go to actual _start */ ldr pc, =_start
*/*********crt0.S********************/*
_start:
/* Setup a stack for ourselves. */ ldr sp, =_stack_top*/* Setup bootinfo. The pointer to the bootinfo struct starts in 'r0'.
*/*
**
- bl seL4_InitBootInfo //Since R0 has been modified by
_sel4_start, sel4_InitBootInfo will not run correctly.*
/* Call constructors and other initialisation functions. */ bl _init /* Call main. */ bl main b exitBest Regards,
Shijun Zhao
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