ArmPlatformPkg/ArmPlatformStackLib: use callee preserved registers

The entry code in ArmPlatformStackSet () is a 1:1 transliteration of the
ARM version, which uses the callee preserved registers r3 - r7 (*) to
preserve the function arguments and the link register across a call to
ArmPlatformIsPrimaryCore ().

However, x3 - x7 are not callee preserved on AARCH64, and so we should use
registers >= x19 instead. While we're at it, drop an unnecessary preserve
of the link register, and simplify/deobfuscate the calculation of the
secondary stack position.

(*) Note that r3 is not actually a callee saved register even on ARM.

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

1 files changed, 19 insertions, 24 deletions

diff --git a/ArmPlatformPkg/Library/ArmPlatformStackLib/AArch64/ArmPlatformStackLib.S b/ArmPlatformPkg/Library/ArmPlatformStackLib/AArch64/ArmPlatformStackLib.S
index 65d7d6c6d6..e219d53cb7 100644
--- a/ArmPlatformPkg/Library/ArmPlatformStackLib/AArch64/ArmPlatformStackLib.S
+++ b/ArmPlatformPkg/Library/ArmPlatformStackLib/AArch64/ArmPlatformStackLib.S
@@ -22,13 +22,13 @@
 //  );

 ASM_FUNC(ArmPlatformStackSet)

   // Save parameters

-  mov   x6, x3

-  mov   x5, x2

-  mov   x4, x1

-  mov   x3, x0

+  mov   x26, x3

+  mov   x25, x2

+  mov   x24, x1

+  mov   x23, x0

 

   // Save the Link register

-  mov   x7, x30

+  mov   x27, x30

 

   // Identify Stack

   mov   x0, x1

@@ -36,13 +36,13 @@ ASM_FUNC(ArmPlatformStackSet)
   cmp   x0, #1

 

   // Restore parameters

-  mov   x0, x3

-  mov   x1, x4

-  mov   x2, x5

-  mov   x3, x6

+  mov   x0, x23

+  mov   x1, x24

+  mov   x2, x25

+  mov   x3, x26

 

   // Restore the Link register

-  mov   x30, x7

+  mov   x30, x27

 

   b.ne  0f

 

@@ -57,10 +57,7 @@ ASM_FUNC(ArmPlatformStackSet)
 //  IN UINTN SecondaryStackSize

 //  );

 ASM_FUNC(ArmPlatformStackSetPrimary)

-  // Save the Link register

-  mov   x4, x30

-

-  // Add stack of primary stack to StackBase

+  // Add size of primary stack to StackBase

   add   x0, x0, x2

 

   // Compute SecondaryCoresCount * SecondaryCoreStackSize

@@ -70,7 +67,7 @@ ASM_FUNC(ArmPlatformStackSetPrimary)
   // Set Primary Stack ((StackBase + PrimaryStackSize) + (SecondaryCoresCount * SecondaryCoreStackSize))

   add   sp, x0, x3

 

-  br    x4

+  ret

 

 //VOID

 //ArmPlatformStackSetSecondary (

@@ -81,30 +78,28 @@ ASM_FUNC(ArmPlatformStackSetPrimary)
 //  );

 ASM_FUNC(ArmPlatformStackSetSecondary)

   // Save the Link register

-  mov   x4, x30

+  mov   x24, x30

   mov   sp, x0

 

   // Get Core Position

   mov   x0, x1

   bl    ASM_PFX(ArmPlatformGetCorePosition)

-  mov   x5, x0

+  mov   x25, x0

 

   // Get Primary Core Position

   bl    ASM_PFX(ArmPlatformGetPrimaryCoreMpId)

   bl    ASM_PFX(ArmPlatformGetCorePosition)

 

   // Get Secondary Core Position. We should get consecutive secondary stack number from 1...(CoreCount-1)

-  cmp   x5, x0

-  b.ls  1f

+  cmp   x25, x0

+

   // Decrement the position if after the primary core

-  sub   x5, x5, #1

-1:

-  add   x5, x5, #1

+  cinc  x25, x25, ls

 

   // Compute top of the secondary stack

-  mul   x3, x3, x5

+  mul   x3, x3, x25

 

   // Set stack

   add   sp, sp, x3

 

-  br    x4

+  ret   x24