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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 */ common_start: 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_bssComparing 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. Cheers, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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