Re: Discussion about why GNU/Linux system upgrades cause old programs to break

> From: Arsen Arsenović <[email protected]>
> Cc: [email protected],  [email protected]
> Date: Wed, 12 Aug 2026 20:34:59 +0200
> 
> > Does Emacs 27 specify an option that implies "reject K&R syntax"
> > or "complain about anything that doesn't satisfy the C99 spec?"
> 
> Yes, it will specifically pass -std=gnu11 to a C89 compiler:
> 
>   /tmp/emacs-27.1$ ./configure CC='gcc -std=gnu89' --with-jpeg=no --with-gif=no
>   [...]
>     What compiler should emacs be built with?               gcc -std=gnu89 -std=gnu11 -g3 -O2
>   [...]

Correction: the -std=gnu11 option will be passed to the compiler only
if needed and supported.  Emacs (starting from v25.1) requires C99, it
does not require C11.

> > Does GCC offer an option to allow K&R function definitions along with
> > the features of C99, which could have been used in compiling Emacs 27?
> 
> Yes, though Emacs 27 doesn't need it, by passing -std=c89.
> 
> But, gcc allows you to recover the old behavior (of permitting cetain
> K&R constructs in C99 and onwards) also, by passing:
> 
>   -Wno-error=implicit-function-declaration
>   -Wno-error=declaration-missing-parameter-type
>   -Wno-error=return-mismatch
>   -Wno-error=int-conversion
>   -Wno-error=incompatible-pointer-types

Sadly, the GCC manual, even the latest one which ships with GCC 16.2,
does not have an index entry that matches "K&R", so users who want to
know how to disable the warnings and errors when compiling such
programs have an uphill battle to fight to discover these options.

> Emacs 27 builds fine actually.
> 
> The error that was originally being discussed was not a break in the
> toolchain, just a system administration error.

The problem with SIGSTKSZ, which breaks the original Emacs 27.1
sources, is not a system administration error.  But yes, Emacs 27
doesn't have problems with K&R syntax, that was a misunderstanding.