[PATCH v2 01/10] ldbl-128ibm-compat: workaround C++ redirect limitations

[Paul E Murphy]

On 3/27/20 4:34 PM, Joseph Myers wrote:
> On Fri, 27 Mar 2020, Paul E. Murphy via Libc-alpha wrote:
> 
>> GCC 8+ is more pedantic about type checking the redirect declarations
>> for non-system headers.  I am not sure if there is less obtrusive way
>> to dodge these warnings when building C++ tests using the headers from
>> the glibc under construction.

How about the following commit message body?

GCC 9.2 is more pedantic about type checking the redirect declarations
for non-system headers.  I am not sure if there is less obtrusive way
to dodge these warnings when building C++ tests using the headers from
the glibc under construction.

Many errors of the following form appear:

In file included from ../include/sys/cdefs.h:3,
                  from ../include/features.h:465,
                  from ../bits/libc-header-start.h:33,
                  from ../math/math.h:27,
                  from ../include/math.h:7,
                  from test-math-isinff.cc:21:
../libio/bits/stdio-ldbl.h:25:20: error: declaration of ‘int 
sprintf(char*, const char*, ...)’ has a different exception specifier
    25 | __LDBL_REDIR_DECL (sprintf)
       |                    ^~~~~~~
../misc/sys/cdefs.h:461:26: note: in definition of macro ‘__LDBL_REDIR_DECL’
   461 |   extern __typeof (name) name __asm (__ASMNAME ("__" #name 
"ieee128"));
       |                          ^~~~
In file included from ../include/stdio.h:5,
                  from test-math-isinff.cc:22:
../libio/stdio.h:334:12: note: from previous declaration ‘int 
sprintf(char*, const char*, ...) throw ()’
   334 | extern int sprintf (char *__restrict __s,
       |            ^~~~~~~


> 
> The first thing you need to include in the commit message for such a
> change is *the exact diagnostics you're trying to avoid*.  Only given
> those diagnostics can we try to work out a better fix.
> 
I noticed this occurs on FSF GCC 9.2, but not 9.3 and newer.  The 
documentation is vague about which warnings and errors are disabled by 
system_header pragma.