From: Stephen Warren swarren@nvidia.com
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 --- arch/arm/Kconfig | 13 +++++++++++++ arch/arm/lib/crt0_64.S | 3 +++ 2 files changed, 16 insertions(+)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index f2c35e32c649..93b93c142929 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -19,6 +19,19 @@ config POSITION_INDEPENDENT from almost any address. This logic relies on the relocation information that is embedded into the binary to support U-Boot relocating itself to the top-of-RAM later during execution. + +config SYS_INIT_SP_BSS_OFFSET + int + help + U-Boot typically uses a hard-coded value for the stack pointer + before relocation. Define this option 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. endif
config STATIC_RELA diff --git a/arch/arm/lib/crt0_64.S b/arch/arm/lib/crt0_64.S index 9cb70552feda..a181283e0fa9 100644 --- a/arch/arm/lib/crt0_64.S +++ b/arch/arm/lib/crt0_64.S @@ -73,6 +73,9 @@ ENTRY(_main) ldr x0, =(CONFIG_TPL_STACK) #elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK) ldr x0, =(CONFIG_SPL_STACK) +#elif defined(CONFIG_SYS_INIT_SP_BSS_OFFSET) + adr x0, __bss_start + add x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET #else ldr x0, =(CONFIG_SYS_INIT_SP_ADDR) #endif