Align and pad code segments to 64k

Align and pad code segments to 64k

Fiddle the linker scripts to ensure that the code segment starts and ends
on a 64k boundary and the end is padded with valid instructions (nop).
This is necessary to permit direct mapping of code segments from files.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3371
TEST= toolchain trybot and inspection of binaries

R=mseaborn@chromium.org

Committed: https://git.chromium.org/gitweb?p=native_client/nacl-glibc.git;a=commit;h=cd98ee3

[Mark Seaborn, 2013-04-05 20:05:51]

LGTM, but please explain in the commit message that the reason for this is so
that the code segment can be mmapped, and set BUG= to a relevant bug for
mmapping code.

[Roland McGrath, 2013-04-05 20:12:02]

Committed patchset #1 manually as rcd98ee3 (presubmit successful).

[kmixter1, 2013-04-09 04:11:24]

Any reason not to do this for -static links too?  (IOW, modify *.x.static linker
scripts)  I have this as part of a change I was cooking and not sure if I should
land those for completeness or there's a reason not to.

[Mark Seaborn, 2013-04-09 16:44:35]

On 8 April 2013 21:11, <kmixter@chromium.org> wrote:

> Any reason not to do this for -static links too?  (IOW, modify *.x.static
> linker
> scripts)  I have this as part of a change I was cooking and not sure if I
> should
> land those for completeness or there's a reason not to.
>

I thought the *.static linker scripts already align and pad the code
segments to 64k.  But maybe they align but don't NOP-pad?  In that case,
yes, it would be good to change them too, although the static linking
scripts for glibc are rarely used.

Mark

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[kmixter1, 2013-04-09 20:43:24]

OK, my change still has the changes to x.static's and I took all of
Roland's changes to the others.  You're right - they're missing appropriate
padding out to keep the later sections from encroaching on the otherwise
potentially PROT_EXEC mappable page.  PTAL.


On Tue, Apr 9, 2013 at 9:44 AM, Mark Seaborn <mseaborn@chromium.org> wrote:

> On 8 April 2013 21:11, <kmixter@chromium.org> wrote:
>
>> Any reason not to do this for -static links too?  (IOW, modify *.x.static
>> linker
>> scripts)  I have this as part of a change I was cooking and not sure if I
>> should
>> land those for completeness or there's a reason not to.
>>
>
> I thought the *.static linker scripts already align and pad the code
> segments to 64k.  But maybe they align but don't NOP-pad?  In that case,
> yes, it would be good to change them too, although the static linking
> scripts for glibc are rarely used.
>
> Mark
>
>

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