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ArmPlatformPkg/Sec: fix return_from_exception code and comment 

The return_from_exception implementation in Sec/Helper.S (the GCC
version) deviates from the RVCT version, in a way that suggests that
both may have been broken at some point, and that they weren't fixed
in the same way nor at the same time.

So bring the GCC version in line with the RVCT version, and at the
same time, deobfuscate the comment.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19244 6f19259b-4bc3-4df7-8a09-765794883524
This commit is contained in:
Ard Biesheuvel 2015-12-14 16:08:27 +00:00 committed by abiesheuvel
parent aaa0820553
commit 949973b6c0
2 changed files with 6 additions and 17 deletions
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17
ArmPlatformPkg/Sec/Arm/Helper.S
View File

@ -46,20 +46,11 @@ ASM_PFX(enter_monitor_mode):
bx r4
# We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
# When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
# 'pc'; we will not change the CPSR flag and it will crash.
# The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
# Return-from-exception is not an interworking return, so we must do it
# in two steps, in case r0 has the Thumb bit set.
ASM_PFX(return_from_exception):
ldr lr, returned_exception
#The following instruction breaks the code.
#movs pc, lr
mrs r2, cpsr
bic r2, r2, #0x1f
orr r2, r2, #0x13
msr cpsr_c, r2
adr lr, returned_exception
movs pc, lr
returned_exception: @ We are now in non-secure state
bx r0

6
ArmPlatformPkg/Sec/Arm/Helper.asm
View File

@ -45,10 +45,8 @@ enter_monitor_mode FUNCTION
bx r4
ENDFUNC
// We cannot use the instruction 'movs pc, lr' because the caller can be written either in ARM or Thumb2 assembler.
// When we will jump into this function, we will set the CPSR flag to ARM assembler. By copying directly 'lr' into
// 'pc'; we will not change the CPSR flag and it will crash.
// The way to fix this limitation is to do the movs into the ARM assmbler code and then do a 'bx'.
// Return-from-exception is not an interworking return, so we must do it
// in two steps, in case r0 has the Thumb bit set.
return_from_exception
adr lr, returned_exception
movs pc, lr