On Mon, Jul 31, 2017 at 07:55:34AM -0600, Jan Beulich wrote: > >>> Konrad Rzeszutek Wilk <kon...@kernel.org> 07/26/17 9:50 PM >>> > >--- a/docs/misc/livepatch.markdown > >+++ b/docs/misc/livepatch.markdown > >@@ -279,6 +279,10 @@ It may also have some architecture-specific sections. > >For example: > >* Exception tables. > >* Relocations for each of these sections. > > > >+Note that on ARM 32 the sections SHOULD be four byte aligned. Otherwise > >+we risk hitting Data Abort exception as un-aligned manipulation of data is > >+prohibited on ARM 32. > > This (and hence the rest of the patch) is not in line with the outcome of the > earlier discussion we had. Nothing is wrong with a section having smaller > alignment, as long as there are no 32-bit (or wider, but I don't think there > are any such) relocations against such a section. And even if there were, I > think it should rather be the code doing the relocations needing to cope, as > I don't think the ARM ELF ABI imposes any such restriction.
The idea behind this patch is to give advance warnings. Akin to what 2ff229643b739e2fd0cd0536ee9fca506cfa92f8 "xen/livepatch: Don't crash on encountering STN_UNDEF relocations" did. The other patches in this series fix the alignment issues. The ARM ELF ABI (http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044f/IHI0044F_aaelf.pdf) says: 4.3.5 Section Alignment There is no minimum alignment required for a section. However, sections containing thumb code must be at least 16-bit aligned and sections containing ARM code must be at least 32-bit aligned. Platform standards may set a limit on the maximum alignment that they can guarantee (normally the page size). _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
