Re: Add macros for diagnostic control, use them in locale/weightwc.h

[Joseph Myers <joseph at codesourcery dot com>]

On Tue, 25 Nov 2014, Paul Eggert wrote:

> On 11/24/2014 05:29 PM, Joseph Myers wrote:
> > We have the nscd/connections.c "ignoring return value of 'setuid', declared
> > with attribute warn_unused_result [-Wunused-result]" (and similar for
> > setgid), in a context where another id-setting call has already failed
> 
> Yes, we've run into that several times in GNU applications and we came up with
> a better way to fix it, in the Gnulib ignore-value module, which defines this:
> 
> # define ignore_value(x) \
>     (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
> 
> One can then write "ignore_value (setuid (server_uid))" instead of "setuid
> (server_uid)".  So we shouldn't need a pragma for this one.

Sure, that can be done if preferred to using pragmas to make it clear this 
is exactly about disabling a diagnostic.

> > We have, for some
> > architecture/compiler combinations, "res_send.c:795:41: warning: 'resplen'
> > may be used uninitialized in this function [-Wmaybe-uninitialized]" (a
> > case where the relevant code only gets executed if the variable is
> > initialized - the first time round a loop will execute a different if
> > branch and cause it to be initialized).
> 
> Neither you nor Roland liked the IF_LINT approach that Gnulib uses for this
> sort of thing, but I hope we can figure out something else to satisfy glibc's
> constraints.  How about something like this?
> 
> #define ASSUME_MEM_INITIALIZED(v) asm ("" : "=m" (v))
> 
> and then write "ASSUME_MEM_INITIALIZED (resplen)" after declaring resplen.

It's only in a particular bit of code where we want to assume it's 
initialized.

-- 
Joseph S. Myers
joseph@codesourcery.com