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Re: [Xen-devel] [PATCH 1/2] xen/arm64: correct comments

Hello Peng,

I would specific the file modified in the title.

On 20/04/16 14:54, Peng Fan wrote:
The 'Base address for 4K mapping' is '(x19 >> THIRD_SHIFT) << THIRD_SHIFT'.

The computation is a sequence of 2 instructions. I gave a look to the rest of the file and the comments are usually put on the first instruction.

So I would much prefer to stay consistent with the rest of the code.

Also we are building 4K page mapping, not section mapping.

To be fair, a page is a specialized section.

Signed-off-by: Peng Fan <van.freenix@xxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
  xen/arch/arm/arm64/head.S | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 946e2c9..05e3db0 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -471,10 +471,10 @@ skip_bss:
          ldr   x4, =boot_third
          add   x4, x4, x20            /* x4 := paddr (boot_third) */

-        lsr   x2, x19, #THIRD_SHIFT  /* Base address for 4K mapping */
-        lsl   x2, x2, #THIRD_SHIFT
-        mov   x3, #PT_MEM_L3         /* x2 := Section map */
-        orr   x2, x2, x3
+        lsr   x2, x19, #THIRD_SHIFT
+        lsl   x2, x2, #THIRD_SHIFT  /* Base address for 4K mapping */
+        mov   x3, #PT_MEM_L3
+        orr   x2, x2, x3            /* x2 := Page map */

The section map is the combination of 2 instructions. With this change we don't know quickly what the purpose of "mov x3, #PT_MEM_L3".

          /* ... map of vaddr(start) in boot_third */
          mov   x1, xzr


Julien Grall

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