diff mbox series

[v2,3/6] arm64: PIE: Allow fixed stack pointer

Message ID 20200930163918.24995-4-andre.przywara@arm.com
State Accepted
Commit 12650e4a46c859eb14e6141b828d92919a18b9c6
Delegated to: Tom Rini
Headers show
Series qemu-arm64: Allow booting via Trusted Firmware | expand

Commit Message

Andre Przywara Sept. 30, 2020, 4:39 p.m. UTC 
Currently selecting CONFIG_POSITION_INDEPENDENT also forces us to use an
initial stack pointer relative to the beginning of the BSS section.
This makes some sense, because this should be writable memory anyway.

However the BSS section is not cleared or used until later in the
setup process (after relocation), so memory nearby might not be
available early enough to host the initial stack. This is an issue if
U-Boot is loaded from (Flash-)ROM, for instance.

Allow CONFIG_INIT_SP_RELATIVE to be turned off by a board's config, to
be able to select a fixed stack pointer, for instance in known good
DRAM.

This will help QEMU utilising PIE, when it's loaded to (Flash-)ROM.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
---
 arch/arm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Tom Rini Oct. 9, 2020, 1:02 p.m. UTC | #1 
On Wed, Sep 30, 2020 at 05:39:15PM +0100, Andre Przywara wrote:

> Currently selecting CONFIG_POSITION_INDEPENDENT also forces us to use an
> initial stack pointer relative to the beginning of the BSS section.
> This makes some sense, because this should be writable memory anyway.
> 
> However the BSS section is not cleared or used until later in the
> setup process (after relocation), so memory nearby might not be
> available early enough to host the initial stack. This is an issue if
> U-Boot is loaded from (Flash-)ROM, for instance.
> 
> Allow CONFIG_INIT_SP_RELATIVE to be turned off by a board's config, to
> be able to select a fixed stack pointer, for instance in known good
> DRAM.
> 
> This will help QEMU utilising PIE, when it's loaded to (Flash-)ROM.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Reviewed-by: Stephen Warren <swarren@nvidia.com>

Applied to u-boot/master, thanks!
diff mbox series

Patch

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b6fb276b6f8..486141478ce 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -12,7 +12,6 @@  config ARM64
 if ARM64
 config POSITION_INDEPENDENT
 	bool "Generate position-independent pre-relocation code"
-	select INIT_SP_RELATIVE
 	help
 	  U-Boot expects to be linked to a specific hard-coded address, and to
 	  be loaded to and run from that address. This option lifts that
@@ -23,6 +22,7 @@  config POSITION_INDEPENDENT
 
 config INIT_SP_RELATIVE
 	bool "Specify the early stack pointer relative to the .bss section"
+	default y if POSITION_INDEPENDENT
 	help
 	  U-Boot typically uses a hard-coded value for the stack pointer
 	  before relocation. Enable this option to instead calculate the