On 6/19/19 9:11 PM, Andrew Cooper wrote:
.data.read_mostly only needs separating from adjacent data by one cache line
to be effective, and placing it adjacent to .data.page_aligned fulfills this
requirement.
For ARM, .ex_table appears to be a vestigial remnant. Nothing in the
resulting build ever inspects or acts on the contents of the table. The arm32
build does however have some assembly routines which fill .ex_table.
Drop all of ARM's .ex_table infrastructure, to reduce the size of the compiled
binary, and avoid giving the illusion of exception handling working.
I am not in favor of this change. assembler.h is meant to be a verbatim
copy of the Linux counterpart.
[...]
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 2b44e5d..3dc5117 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -94,27 +94,13 @@ SECTIONS
_erodata = .; /* End of read-only data */
.data : { /* Data */
+ *(.data.read_mostly)
Before, .data.read_mostly was SMP_CACHE_BYTES aligned. Now, it seems
there are no alignment.
This may end up to have _erodata and .data.read_mostly to be part of the
same page. As Arm enforce read-only, you may crash on access to
.data.read_mostly.
So I think you have
. = ALIGN(PAGE_SIZE)
*(.data.read_mostly)
.align(SMP_CACHE_BYTES).
Cheers,
--
Julien Grall
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