[PATCH] Add private_function for private functions within glibc [BZ #21598]

[H.J. Lu]

On Tue, Aug 8, 2017 at 2:27 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Aug 8, 2017 at 2:12 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>> On Tue, 8 Aug 2017, H.J. Lu wrote:
>>
>>> since shadow stack doesn't match return stack.  We need to use register
>>> indirect branch via %ecx.  That means only 2 parameters can be passed
>>> in registers for external function calls with lazy binding when shadow
>>> stack is enabled.  However, internal_function, which should be used only
>>> with hidden function within libc.so, are also used with private function
>>> calls between different shared objects of glibc.
>>
>> Should we consider it part of the ABI that users' shared objects, not just
>> glibc ones, may export functions with regparm calling convention?  It's
>> certainly possible at present, but I don't know how widely used it is.
>
> Some libraries do that:
>
> https://sourceware.org/ml/libc-alpha/2017-06/msg01091.html
>
> We have a similar issue on x86-64:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=21265
>
> CET enabled compiler should disallow  __attribute__((regparm(3))) on
> i386.  When CET is disabled, __attribute__((regparm(3))) is OK.
>
>>> This patch removes USE_REGPARMS from config.h.in.  Instead, it defines
>>> internal_function and private_function, which is for private function
>>> calss between different shared objects, in config.h.in.  Currently,
>>> sysdeps/i386/configure.ac defines private_function as
>>
>> I'd expect these definitions to go in a sysdeps header (for which i386 has
>> a version overriding the default version), as suggested in
>> <https://sourceware.org/ml/libc-alpha/2014-06/msg00784.html>, rather than
>> being defined directly from a configure.ac file.
>
> I will do that.
>
> Thanks.
>

Here is the updated patch.

Tested on i686 and x86-64.  Any more comments?

Thanks.


-- 
H.J.
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