ToT build error with ToT GCC on Aarch64

[Martin Sebor]

On 07/23/2018 12:29 PM, Martin Sebor wrote:
> On 07/23/2018 11:26 AM, Florian Weimer wrote:
>> On 07/23/2018 06:19 PM, Jeff Law wrote:
>>> On 07/23/2018 09:51 AM, Steve Ellcey wrote:
>>>> I have run into a problem when building the ToT glibc with the ToT
>>>> GCC on
>>>> Aarch64.  I haven't dug into this enough to know if this is a GCC
>>>> problem,
>>>> a glibc problem, or just a message that needs to be ignored but I
>>>> wanted to
>>>> send out an email in case this is something that needs to be addressed
>>>> before GCC 2.28 is released.
>>
>>> Martin S. and I are already looking at this and I've already asked
>>> Martin to bring in Carlos and Florian.
>>
>> Would it be possible to print the full inlining stack for these GCC
>> warnings?  I don't see a %K format specifier (or whatever is used for
>> this).
>>
>> I think it would make it a bit easier to track these down.
>
> It's one of my own pet peeves with the -Warray-bounds warnings
> that they don't do that.  I've quickly hacked GCC to print
> the inlining stack.  It doesn't look to me like it helps that
> much but I'll let you be the judge:
>
> In file included from fnmatch.c:244:
> In function ‘findidxwc’,
>     inlined from ‘internal_fnwmatch’ at fnmatch_loop.c:404:10:
> ../locale/weightwc.h:124:28: warning: array subscript 1 is outside array
> bounds of ‘wint_t[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]

Here's a bit more context showing the variable being referenced
(for simplicity, GCC takes singleton objects as arrays of one
element):

In file included from fnmatch.c:244:
In function ‘findidxwc’,
     inlined from ‘internal_fnwmatch’ at fnmatch_loop.c:404:10:
../locale/weightwc.h:124:28: error: array subscript 1 is outside array 
bounds of ‘wint_t[1]’ {aka ‘unsigned int[1]’} [-Werror=array-bounds]
     if (cp[nhere - 1] > usrc[nhere -1])
                         ~~~~^~~~~~~~~~
In file included from fnmatch.c:315:
fnmatch_loop.c: In function ‘internal_fnwmatch’:
fnmatch_loop.c:342:13: note: while referencing ‘str’
        UCHAR str;
              ^~~

There's an interesting comment above the declaration:

     /* It's important that STR be a scalar variable rather
        than a one-element array, because GCC (at least 4.9.2
        -O2 on x86-64) can be confused by the array and
        diagnose a "used initialized" in a dead branch in the
        findidx function.  */
     UCHAR str;

Martin