Hello,
I am not (yet) good at ARM assembler syntax and instructions, so trying to understand the start.S code is not very easy for me. However I think I saw some places there that need clarification. All what I see as suspiscious I have marked with $$$ and just comments with %%% in the next line.
... .globl _bss_start_ofs _bss_start_ofs: .word __bss_start - _start
.globl _bss_end_ofs _bss_end_ofs: .word _end - _start %%% both yield constants that are in TEXT and can be accessed %%% PC relative, right? ... reset: /* * set the cpu to SVC32 mode */ mrs r0,cpsr bic r0,r0,#0x1f orr r0,r0,#0xd3 msr cpsr,r0 %%% just style: the rest uses spaces after the comma. /* * we do sys-critical inits only at reboot, * not when booting from ram! */ #ifndef CONFIG_SKIP_LOWLEVEL_INIT bl cpu_init_crit #endif
/* Set stackpointer in internal RAM to call board_init_f */ call_board_init_f: ldr sp, =(CONFIG_SYS_INIT_SP_ADDR) ldr r0,=0x00000000 %%% style bl board_init_f
/*------------------------------------------------------------------------------*/
/* * void relocate_code (addr_sp, gd, addr_moni) * * This "function" does not return, instead it continues in RAM * after relocating the monitor code. * */ .globl relocate_code relocate_code: mov r4, r0 /* save addr_sp */ mov r5, r1 /* save addr of gd */ mov r6, r2 /* save addr of destination */ mov r7, r2 /* save addr of destination */
/* Set up the stack */ stack_setup: mov sp, r4
adr r0, _start %%% adr reg, label sets reg to the address of label? %%% ldr reg, label sets reg to the content of mem at label? ldr r2, _TEXT_BASE $$$ r2 is overwritten two lines below, right? ldr r3, _bss_start_ofs add r2, r0, r3 /* r2 <- source end address */ cmp r0, r6 beq clear_bss
copy_loop: ldmia r0!, {r9-r10} /* copy from source address [r0] */ stmia r6!, {r9-r10} /* copy to target address [r1] */ cmp r0, r2 /* until source end address [r2] */ blo copy_loop
#ifndef CONFIG_PRELOADER /* * fix .rel.dyn relocations */ ldr r0, _TEXT_BASE /* r0 <- Text base */ %%% why are we using _TEXT_BASE here and not _start? sub r9, r7, r0 /* r9 <- relocation offset */ ldr r10, _dynsym_start_ofs /* r10 <- sym table ofs */ add r10, r10, r0 /* r10 <- sym table in FLASH */ ldr r2, _rel_dyn_start_ofs /* r2 <- rel dyn start ofs */ add r2, r2, r0 /* r2 <- rel dyn start in FLASH */ ldr r3, _rel_dyn_end_ofs /* r3 <- rel dyn end ofs */ add r3, r3, r0 /* r3 <- rel dyn end in FLASH */ fixloop: ldr r0, [r2] /* r0 <- location to fix up, IN FLASH! */ add r0, r0, r9 /* r0 <- location to fix up in RAM */ ldr r1, [r2, #4] and r8, r1, #0xff cmp r8, #23 /* relative fixup? */ beq fixrel cmp r8, #2 /* absolute fixup? */ beq fixabs /* ignore unknown type of fixup */ b fixnext fixabs: /* absolute fix: set location to (offset) symbol value */ mov r1, r1, LSR #4 /* r1 <- symbol index in .dynsym */ add r1, r10, r1 /* r1 <- address of symbol in table */ ldr r1, [r1, #4] /* r1 <- symbol value */ add r1, r9 /* r1 <- relocated sym addr */ b fixnext fixrel: /* relative fix: increase location by offset */ ldr r1, [r0] add r1, r1, r9 fixnext: str r1, [r0] add r2, r2, #8 /* each rel.dyn entry is 8 bytes */ cmp r2, r3 blo fixloop #endif
clear_bss: #ifndef CONFIG_PRELOADER ldr r0, _bss_start_ofs %%% r0 = __bss_start - _start ldr r1, _bss_end_ofs %%% r1 = _end - _start ldr r3, _TEXT_BASE /* Text base */ $$$ r3 is not used below this mov r4, r7 /* reloc addr */ %%% why move it to r4? could we not add r7 in the next 2 lines? add r0, r0, r4 %%% ok, this yields r0 = __bss_start - _start + "relocated address" add r1, r1, r4 %%% ok, this yields r1 = _end - _start + "relocated address" mov r2, #0x00000000 /* clear */
clbss_l:str r2, [r0] /* clear loop... */ add r0, r0, #4 cmp r0, r1 bne clbss_l %%% this should better be blo, just in case _end is not aligned?
%%% I cannot see anything here that would prevent BSS being cleared. bl coloured_LED_init bl red_LED_on #endif
/* * We are done. Do not return, instead branch to second part of board * initialization, now running from RAM. */ #ifdef CONFIG_NAND_SPL ldr r0, _nand_boot_ofs mov pc, r0
_nand_boot_ofs: .word nand_boot #else ldr r0, _board_init_r_ofs adr r1, _start add lr, r0, r1 add lr, lr, r9 /* setup parameters for board_init_r */ mov r0, r5 /* gd_t */ mov r1, r7 /* dest_addr */ /* jump to it ... */ mov pc, lr ...
Best Regards, Reinhard