[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] xen/arm64: Don't zero BSS when booting using EFI

On 03/02/17 14:31, Jan Beulich wrote:
On 03.02.17 at 15:24, <julien.grall@xxxxxxx> wrote:
On 03/02/17 07:41, Jan Beulich wrote:
On 02.02.17 at 20:25, <julien.grall@xxxxxxx> wrote:
@@ -261,6 +265,8 @@ GLOBAL(init_secondary)
         sub   x20, x19, x0           /* x20 := phys-offset */

         mov   x22, #1                /* x22 := is_secondary_cpu */
+        /* Skip zero BSS on secondary CPUs to avoid nasty surprises. */
+        mov   x26, #1                /* X26 := skip_zero_bss */

         mov   x24, #0                /* x24 := CPU ID. Initialy zero until we
@@ -314,8 +320,8 @@ common_start:

 el2:    PRINT("- Xen starting at EL2 -\r\n")

-        /* Zero BSS On the boot CPU to avoid nasty surprises */
-        cbnz  x22, skip_bss
+        /* Zero BSS only when requested to avoid nasty surprises. */
+        cbnz  x26, skip_bss

Comparing the original comment here with both this and the
earlier hunk, I think the intended meaning is lost. Zeroing the
BSS on secondary CPUs is certainly a bug, not a nasty surprise.
What I think the original comment is meaning to say is "the
BSS should have been zeroed already, but let's better not rely
on that".

This is not the original meaning.

Are you sure the comment wasn't just copied from x86 code?

Maybe. Regardless that I think the code holds on ARM in both case.

It is a nasty surprises when zero BSS on secondary CPU or EFI because we loose all the information.

On non-EFI setup BSS will not be
zeroed before hand as the loader of Xen does not know the size of BSS.

So I would recommend correcting the comments at once to reflect
what they are now supposed to mean.

IHMO, the comment is valid. See why above.


Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.