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ARMv8: Allow dynamic early stack pointer

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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>
This commit is contained in:
Stephen Warren 2017-12-19 18:30:36 -07:00 committed by Tom Warren
parent 0d1bd150f0
commit e6c904489a
2 changed files with 16 additions and 0 deletions
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13
arch/arm/Kconfig
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@ -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

3
arch/arm/lib/crt0_64.S
View File

@ -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