mirror of
https://github.com/brain-hackers/u-boot-brain
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e6c904489a
U-Boot typically uses a hard-coded value for the stack pointer before relocation. Implement option SYS_INIT_SP_BSS_OFFSET to instead calculate the initial SP at run-time. This is useful to avoid hard-coding addresses into U-Boot, so that can be loaded and executed at arbitrary addresses and thus avoid using arbitrary addresses at runtime. This option's value is the offset added to &_bss_start in order to calculate the stack pointer. This offset should be large enough so that the early malloc region, global data (gd), and early stack usage do not overlap any appended DTB. Signed-off-by: Stephen Warren <swarren@nvidia.com> Signed-off-by: Tom Warren <twarren@nvidia.com>
158 lines
4.9 KiB
ArmAsm
158 lines
4.9 KiB
ArmAsm
/*
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* crt0 - C-runtime startup Code for AArch64 U-Boot
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*
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* (C) Copyright 2013
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* David Feng <fenghua@phytium.com.cn>
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*
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* (C) Copyright 2012
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* Albert ARIBAUD <albert.u.boot@aribaud.net>
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*
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* SPDX-License-Identifier: GPL-2.0+
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*/
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#include <config.h>
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#include <asm-offsets.h>
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#include <asm/macro.h>
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#include <linux/linkage.h>
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/*
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* This file handles the target-independent stages of the U-Boot
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* start-up where a C runtime environment is needed. Its entry point
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* is _main and is branched into from the target's start.S file.
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*
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* _main execution sequence is:
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*
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* 1. Set up initial environment for calling board_init_f().
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* This environment only provides a stack and a place to store
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* the GD ('global data') structure, both located in some readily
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* available RAM (SRAM, locked cache...). In this context, VARIABLE
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* global data, initialized or not (BSS), are UNAVAILABLE; only
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* CONSTANT initialized data are available. GD should be zeroed
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* before board_init_f() is called.
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*
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* 2. Call board_init_f(). This function prepares the hardware for
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* execution from system RAM (DRAM, DDR...) As system RAM may not
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* be available yet, , board_init_f() must use the current GD to
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* store any data which must be passed on to later stages. These
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* data include the relocation destination, the future stack, and
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* the future GD location.
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*
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* 3. Set up intermediate environment where the stack and GD are the
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* ones allocated by board_init_f() in system RAM, but BSS and
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* initialized non-const data are still not available.
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*
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* 4a.For U-Boot proper (not SPL), call relocate_code(). This function
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* relocates U-Boot from its current location into the relocation
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* destination computed by board_init_f().
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*
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* 4b.For SPL, board_init_f() just returns (to crt0). There is no
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* code relocation in SPL.
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*
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* 5. Set up final environment for calling board_init_r(). This
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* environment has BSS (initialized to 0), initialized non-const
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* data (initialized to their intended value), and stack in system
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* RAM (for SPL moving the stack and GD into RAM is optional - see
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* CONFIG_SPL_STACK_R). GD has retained values set by board_init_f().
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*
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* TODO: For SPL, implement stack relocation on AArch64.
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*
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* 6. For U-Boot proper (not SPL), some CPUs have some work left to do
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* at this point regarding memory, so call c_runtime_cpu_setup.
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*
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* 7. Branch to board_init_r().
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*
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* For more information see 'Board Initialisation Flow in README.
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*/
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ENTRY(_main)
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/*
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* Set up initial C runtime environment and call board_init_f(0).
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*/
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#if defined(CONFIG_TPL_BUILD) && defined(CONFIG_TPL_NEEDS_SEPARATE_STACK)
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ldr x0, =(CONFIG_TPL_STACK)
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#elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
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ldr x0, =(CONFIG_SPL_STACK)
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#elif defined(CONFIG_SYS_INIT_SP_BSS_OFFSET)
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adr x0, __bss_start
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add x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET
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#else
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ldr x0, =(CONFIG_SYS_INIT_SP_ADDR)
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#endif
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bic sp, x0, #0xf /* 16-byte alignment for ABI compliance */
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mov x0, sp
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bl board_init_f_alloc_reserve
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mov sp, x0
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/* set up gd here, outside any C code */
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mov x18, x0
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bl board_init_f_init_reserve
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mov x0, #0
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bl board_init_f
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#if !defined(CONFIG_SPL_BUILD)
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/*
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* Set up intermediate environment (new sp and gd) and call
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* relocate_code(addr_moni). Trick here is that we'll return
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* 'here' but relocated.
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*/
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ldr x0, [x18, #GD_START_ADDR_SP] /* x0 <- gd->start_addr_sp */
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bic sp, x0, #0xf /* 16-byte alignment for ABI compliance */
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ldr x18, [x18, #GD_NEW_GD] /* x18 <- gd->new_gd */
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adr lr, relocation_return
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#if CONFIG_POSITION_INDEPENDENT
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/* Add in link-vs-runtime offset */
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adr x0, _start /* x0 <- Runtime value of _start */
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ldr x9, _TEXT_BASE /* x9 <- Linked value of _start */
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sub x9, x9, x0 /* x9 <- Run-vs-link offset */
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add lr, lr, x9
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#endif
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/* Add in link-vs-relocation offset */
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ldr x9, [x18, #GD_RELOC_OFF] /* x9 <- gd->reloc_off */
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add lr, lr, x9 /* new return address after relocation */
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ldr x0, [x18, #GD_RELOCADDR] /* x0 <- gd->relocaddr */
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b relocate_code
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relocation_return:
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/*
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* Set up final (full) environment
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*/
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bl c_runtime_cpu_setup /* still call old routine */
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#endif /* !CONFIG_SPL_BUILD */
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#if defined(CONFIG_SPL_BUILD)
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bl spl_relocate_stack_gd /* may return NULL */
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/* set up gd here, outside any C code, if new stack is returned */
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cmp x0, #0
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csel x18, x0, x18, ne
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/*
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* Perform 'sp = (x0 != NULL) ? x0 : sp' while working
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* around the constraint that conditional moves can not
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* have 'sp' as an operand
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*/
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mov x1, sp
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cmp x0, #0
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csel x0, x0, x1, ne
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mov sp, x0
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#endif
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/*
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* Clear BSS section
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*/
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ldr x0, =__bss_start /* this is auto-relocated! */
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ldr x1, =__bss_end /* this is auto-relocated! */
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clear_loop:
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str xzr, [x0], #8
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cmp x0, x1
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b.lo clear_loop
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/* call board_init_r(gd_t *id, ulong dest_addr) */
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mov x0, x18 /* gd_t */
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ldr x1, [x18, #GD_RELOCADDR] /* dest_addr */
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b board_init_r /* PC relative jump */
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/* NOTREACHED - board_init_r() does not return */
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ENDPROC(_main)
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