[v2,2/5] Remove getc and putc macros from the public stdio.h.

  The getc and putc macros in the public stdio.h expand to call _IO_getc
and _IO_putc respectively.  As _IO_getc, fgetc, and getc are all aliases
for the same function, and _IO_putc, fputc, and putc are also all aliases
for the same function, the macros are pointless.  The C standard does
not require getc and putc to be macros, so let's just not have macros.
All four symbols are exported from libc.so at the same, ancient symbol
version, so there should be no risks for binary compatibility.  Similarly,
the getchar and putchar inlines in bits/stdio.h forward to getc and putc
instead of their _IO_ aliases.

As a change from longstanding historical practice, this does seem
like it might break _something_, so there is a note in NEWS, which
is also a convenient place to advise people that if they thought getc
and putc had reduced per-character overhead they should consider using
getc_unlocked and putc_unlocked instead.  (These are also not macros,
but when optimizing, they are inlines.)

This patch changes installed stripped libraries, since several of the
ancillary libraries and programs use getc and/or putc, so they
formerly referenced _IO_getc / _IO_putc.

	* libio/stdio.h: Don't define getc or putc as macros.
	* libio/bits/stdio.h (getchar, putchar): Use getc and putc,
	not _IO_getc and _IO_putc.
---
 NEWS               | 7 +++++++
 libio/bits/stdio.h | 4 ++--
 libio/stdio.h      | 8 --------
 3 files changed, 9 insertions(+), 10 deletions(-)
  

On Mon, 5 Feb 2018, Zack Weinberg wrote:

> diff --git a/NEWS b/NEWS
> index 3ac57eca4ee..eceab2b2be2 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -15,6 +15,13 @@ Deprecated and removed features, and other changes affecting compatibility:
>  
>    [Add deprecations, removals and changes affecting compatibility here]
>  
> + * The stdio.h functions 'getc' and 'putc' are no longer defined as macros.
> +   This was never required by the C standard, and the macros just expanded
> +   to call alternative names for the same functions.  If you hoped getc and
> +   putc would provide performance improvements over fgetc and fputc, instead
> +   investigate using (f)getc_unlocked and (f)putc_unlocked, and, if
> +   necessary, flockfile and funlockfile.

The "[Add deprecations, removals and changes affecting compatibility 
here]" placeholder should be removed by this patch, as the first one to 
put something in this section for 2.28.

The patch is OK with that change.

There is a theoretical use for implementation-namespace aliases of even 
C90 standard functions such as getc and putc - properly, if a function is 
used in a *macro* defined in a standard header, it should be used via such 
an alias to avoid possible shadowing of the standard function name by a 
block-scope variable in a scope where the macro is used (standard function 
names aren't generally reserved with block scope).  But that doesn't 
affect this patch at all, since there are no such macros making use of 
either getc or putc (and in any case, the _IO_getc and _IO_putc function 
exports still exist should they prove to be of use in future, and any 
aliases for this issue could be defined in headers with asm redirection 
without needing library exports at all).
  

On Mon, Feb 5, 2018 at 7:01 PM, Joseph Myers <joseph@codesourcery.com> wrote:
> On Mon, 5 Feb 2018, Zack Weinberg wrote:
>> diff --git a/NEWS b/NEWS
>> index 3ac57eca4ee..eceab2b2be2 100644
>> --- a/NEWS
>> +++ b/NEWS
>> @@ -15,6 +15,13 @@ Deprecated and removed features, and other changes affecting compatibility:
>>
>>    [Add deprecations, removals and changes affecting compatibility here]
>>
>> + * The stdio.h functions 'getc' and 'putc' are no longer defined as macros.
>> +   This was never required by the C standard, and the macros just expanded
>> +   to call alternative names for the same functions.  If you hoped getc and
>> +   putc would provide performance improvements over fgetc and fputc, instead
>> +   investigate using (f)getc_unlocked and (f)putc_unlocked, and, if
>> +   necessary, flockfile and funlockfile.
>
> The "[Add deprecations, removals and changes affecting compatibility
> here]" placeholder should be removed by this patch, as the first one to
> put something in this section for 2.28.

Doh! That was a merge botch on my end.

> The patch is OK with that change.

I have made that change and pushed patches 1 and 2 of this series.

Also, the full patchset is now available as git branch
'zack/no-libio-h' if anyone wants to experiment with it.

zw