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Re: [Xen-devel] [PATCH v3 4/4] xen: use SYMBOL everywhere

Hi Stefano,

On 11/8/18 10:27 PM, Stefano Stabellini wrote:
On Thu, 8 Nov 2018, Jan Beulich wrote:
On 06.11.18 at 23:05, <sstabellini@xxxxxxxxxx> wrote:
Use SYMBOL everywhere _stext, _etext, etc. are used. Technically, it
is required when comparing and subtracting pointers [1], but use it
everywhere to avoid confusion.

I think using it when not needed is causing more confusion. Also
why would you then not use it on all other data symbols? The
patch will end up quite a bit more reasonable in size once you drop
the unnecessary changes.

OK, I am happy to do that. It will probably be better that way.

  xen/arch/arm/alternative.c          |  7 ++--
  xen/arch/arm/arm32/livepatch.c      |  2 +-
  xen/arch/arm/arm64/livepatch.c      |  2 +-
  xen/arch/arm/domain_build.c         |  2 +-
  xen/arch/arm/livepatch.c            |  6 +--
  xen/arch/arm/mm.c                   | 17 ++++----
  xen/arch/arm/setup.c                |  8 ++--
  xen/arch/x86/setup.c                | 79 +++++++++++++++++++------------------
  xen/arch/x86/tboot.c                | 12 +++---
  xen/arch/x86/x86_64/machine_kexec.c |  4 +-
  xen/drivers/vpci/vpci.c             |  7 +++-
  xen/include/asm-arm/grant_table.h   |  3 +-
  xen/include/asm-arm/mm.h            |  4 +-
  xen/include/asm-x86/mm.h            |  4 +-
  xen/include/xen/kernel.h            | 24 +++++------
  15 files changed, 97 insertions(+), 84 deletions(-)

Just like for v2: Did you really check you caught them all? The vPCI
ones I had pointed at back then were only an example. Another
example now is xen/common/kernel.c:_cmdline_parse().

It is difficult to catch them all. Any suggestion on how to make sure
there are no leftover (other than waiting for the next QAVerify scan)?

The webpage [1] seems to suggest coverity would be able to catch the undefined behavior fixed in that patch.

I am not sure what version of coverity is used to analyze Xen, but it probably worth to have a try.


[1] https://wiki.sei.cmu.edu/confluence/display/c/ARR36-C.+Do+not+subtract+or+compare+two+pointers+that+do+not+refer+to+the+same+array

Julien Grall

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