The function _stext (called _start in some versions) is usually located in arch/<host>/kernel/head.S.
_Stext sets the initial stack pointer and performs any other functions necessary to create a minimal C runtime environment, like clearing the BSS memory section. _Stext then jumps to start_kernel().
Figure 4 shows part of the code for the Hitachi SH version of _stext.
ENTRY(_stext) ! Initialize Status Register mov.l 1f, r0 ! MD=1, RB=0, BL=0, IMASK=0xF ldc r0, sr ! Initialize global interrupt mask mov #0, r0 ldc r0, r6_bank ! mov.l 2f, r0 mov r0, r15 ! Set initial r15 (stack pointer) mov #0x20, r1 ! shll8 r1 ! r1 = 8192 sub r1, r0 ldc r0, r7_bank ! ... and init_task ! Initialize fpu mov.l 7f, r0 jsr @r0 nop ! Enable cache mov.l 6f, r0 jsr @r0 nop ! Clear BSS area mov.l 3f, r1 add #4, r1 mov.l 4f, r2 mov #0, r0 9: cmp/hs r2, r1 bf/s 9b ! while (r1 < r2) mov.l r0,@-r2 ! Start kernel mov.l 5f, r0 jmp @r0 nop .balign 4 1: .long 0x400000F0 ! MD=1, RB=0, BL=0, FD=0, IMASK=0xF 2: .long SYMBOL_NAME(stack) 3: .long SYMBOL_NAME(__bss_start) 4: .long SYMBOL_NAME(_end) 5: .long SYMBOL_NAME(start_kernel) 6: .long SYMBOL_NAME(cache_init) 7: .long SYMBOL_NAME(fpu_init) |
Figure 4. The Hitachi SH's _stext function.
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