clear bss

[jankobler]

I had problems with uncleared bss. E.g. the static variable pt_inuse was not set to zero.
I think I have found the reason for it.

The values were wrong for:
__k_unpaged__edata
__k_unpaged__end

I think the unpaged bss _kern_unpaged_edata ... _kern_unpaged_edata has to be cleared too.

Therefore the paged bss: _edata ... _end
and the unpaged bss: _kern_unpaged_edata ... _kern_unpaged_edata
are both cleared now in the function pre_init.

The values can be verified by:

${CROSS_TOOLS}/arm-elf32-minix-objdump -xD ${OBJ}/kernel/kernel

[jankobler]

In the file pre_init.c the address values of _k_unpaged* are used.
E.g. instead of _edata, the value __k_unpaged_edata is used.

Source in function pre_init

/* Clear BSS */
memset(&_edata, 0, (u32_t)&_end - (u32_t)&_edata);
memset(&_kern_unpaged_edata, 0, (u32_t)&_kern_unpaged_end - (u32_t)&_kern_unpaged_edata);

When you disassemble the kernel with

${CROSS_TOOLS}/arm-elf32-minix-objdump -xD ${OBJ}/kernel/kernel

you can see that the areas which are cleared by __k_unpaged_memset are really
from __k_unpaged__edata to __k_unpaged__end and
from __k_unpaged__kern_unpaged_edata to __k_unpaged__kern_unpaged_end

disassembly of function pre_init

80200be4 <__k_unpaged_pre_init>:
80200be4: e92d47f0 push {r4, r5, r6, r7, r8, r9, sl, lr}
80200be8: e1a05000 mov r5, r0
80200bec: e59f217c ldr r2, [pc, #380] ; 80200d70 <__k_unpaged_$d>
80200bf0: e1a04001 mov r4, r1
80200bf4: e59f0178 ldr r0, [pc, #376] ; 80200d74 <__k_unpaged_$d+0x4>
80200bf8: e3a01000 mov r1, #0
80200bfc: e0602002 rsb r2, r0, r2
80200c00: eb0004af bl 80201ec4 <__k_unpaged_memset>
80200c04: e59f016c ldr r0, [pc, #364] ; 80200d78 <__k_unpaged_$d+0x8>
80200c08: e59f216c ldr r2, [pc, #364] ; 80200d7c <__k_unpaged_$d+0xc>
80200c0c: e3a01000 mov r1, #0
80200c10: e0602002 rsb r2, r0, r2
80200c14: eb0004aa bl 80201ec4 <__k_unpaged_memset>

used data

80200d70 <__k_unpaged_$d>:
80200d70: 802822cc 80200d74: 8023f000 80200d78: 802059b0 80200d7c: 8021c3d0 

These are the values of

802822cc g *ABS* 00000000 __k_unpaged__end
8023f000 g *ABS* 00000000 __k_unpaged__edata
802059b0 g *ABS* 00000000 __k_unpaged__kern_unpaged_edata
8021c3d0 g *ABS* 00000000 __k_unpaged__kern_unpaged_end

The values point all between . = _kern_phys_base and . += _kern_offset

You can list the variables in the bss sections:

${CROSS_TOOLS}/arm-elf32-minix-objdump -xD ${OBJ}/kernel/kernel | sort | grep bss