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Subject:	Re: [ANNOUNCEMENT] TEST RELEASE: Cygwin 2.10.0-0.1
To:	cygwin AT cygwin DOT com
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From:	Ken Brown <kbrown AT cornell DOT edu>
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Date:	Sat, 20 Jan 2018 07:23:24 -0500
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On 1/19/2018 10:27 PM, Ken Brown wrote:
> On 1/18/2018 6:28 PM, Ken Brown wrote:
>> On 1/18/2018 4:30 PM, Yaakov Selkowitz wrote:
>>> On 2018-01-18 08:35, Ken Brown wrote:
>>>> On 1/17/2018 5:29 PM, Ken Brown wrote:
>>>>> Do we need a new gcc release to go along with the recent ssp changes?
>>>>
>>>> The following commit message seems to answer my question:
>>>>
>>>>      Note that this does require building gcc with --disable-libssp and
>>>>      gcc_cv_libc_provides_ssp=yes.
>>>
>>> Correct.
>>>
>>>> Are there plans to coordinate the release of Cygwin 2.10.0 with a new
>>>> gcc release?  In the meantime, I guess package maintainers have to 
>>>> build
>>>> with -U_FORTIFY_SOURCE in order to test building with Cygwin 
>>>> 2.10.0.  Or
>>>> am I missing something?
>>>
>>> -D_FORTIFY_SOURCE is not the default, so simply omitting it is
>>> sufficient.
>>
>> I was talking about building projects in which _FORTIFY_SOURCE is 
>> defined by default.  That happens, for instance, in the gnulib 
>> subdirectory of the emacs tree, so it may affect other projects that 
>> use gnulib also.
>>
>>> You could also just delete
>>> /usr/lib/gcc/*-pc-cygwin/6.4.0/include/ssp, since we won't need it
>>> anymore and it wasn't even being used properly in the first place.
>>
>> That's a simpler workaround than what I was doing.  Thanks.
> 
> Here's another issue that's come up with _FORTIFY_SOURCE.  One of the 
> emacs source files, fileio.c, makes use of a pointer to readlinkat. 
> [More precisely, the file uses an external function foo() with a 
> parameter 'bar' that's a pointer to a function; foo is called in 
> fileio.c with bar = readlinkat.]
> 
> When _FORTIFY_SOURCE > 0, this leads to an "undefined reference to 
> `__ssp_protected_readlinkat'" linking error.  Does this sound like 
> something that will be fixed with the new gcc release?
> 
> I realize I haven't given you full details, but it might be a few days 
> until I have a chance to extract an STC for this issue, so I thought I'd 
> give it a shot.
> 
> If you can't answer the question based on the information above, I'll 
> make an STC as soon as I can.

I got to this sooner than expected:

$ cat ssp_test.c
#define  _FORTIFY_SOURCE 1
#include <unistd.h>
void foo (ssize_t (*preadlinkat) (int, char const *, char *, size_t));

void baz ()
{
   foo (readlinkat);
}

$ gcc -c -O1 ssp_test.c

$ objdump -x ssp_test.o | grep readlinkat
   6 .rdata$.refptr.__ssp_protected_readlinkat 00000010 
0000000000000000  0000000000000000  00000180  2**4
[...]

Ken

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