Hi Andrew,
On 6/19/19 10:48 PM, Andrew Cooper wrote:
On 19/06/2019 22:28, Julien Grall wrote:
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.
What alternative do you propose then, because having infrastructure that
gives the illusion of exception recovery working is a far worse option
than deviating from Linux.
I learnt the hard way before that trying to adapt a Linux file to Xen
makes very difficult to keep track what's going on.
So my preference here is to just disable the section if they exists.
[...]
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).
These both need to be PAGE_SIZE, or .data.page_aligned can end up having
problems.
Good point, I missed the .data.page_aligned.
Cheers,
--
Julien Grall
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