Use libc_hidden_* for fputs (bug 15105)

  Among other localplt test failures when building with -Os, there are
libc.so PLT references for fputs.  fputs calls normally get redirected
to _IO_fputs by a macro in include/stdio.h (and _IO_fputs in turn uses
libc_hidden_proto), but GCC can convert an fprintf call with a
constant string argument into an fputs call, which of course is then
unaffected by the macro redirection.  (I don't know why this issue
only appears with -Os.)

This patch duly adds a use of libc_hidden_proto for fputs.  I see no
obvious reason why the fputs macro redirection is needed at all, but
this patch does not change it.

Tested for x86_64 (both that it removes this particular localplt
failure for -Os - but other such failures remain so the bug can't yet
be closed - and that the testsuite continues to pass without -Os).

2018-02-13  Joseph Myers  <joseph@codesourcery.com>

	[BZ #15105]
	* include/stdio.h [!_ISOMAC && IS_IN (libc)] (fputs): Use
	libc_hidden_proto.
	* libio/iofputs.c (fputs): Use libc_hidden_weak.
  

On 13/02/2018 16:49, Joseph Myers wrote:
> Among other localplt test failures when building with -Os, there are
> libc.so PLT references for fputs.  fputs calls normally get redirected
> to _IO_fputs by a macro in include/stdio.h (and _IO_fputs in turn uses
> libc_hidden_proto), but GCC can convert an fprintf call with a
> constant string argument into an fputs call, which of course is then
> unaffected by the macro redirection.  (I don't know why this issue
> only appears with -Os.)
> 
> This patch duly adds a use of libc_hidden_proto for fputs.  I see no
> obvious reason why the fputs macro redirection is needed at all, but
> this patch does not change it.
> 
> Tested for x86_64 (both that it removes this particular localplt
> failure for -Os - but other such failures remain so the bug can't yet
> be closed - and that the testsuite continues to pass without -Os).
> 
> 2018-02-13  Joseph Myers  <joseph@codesourcery.com>
> 
> 	[BZ #15105]
> 	* include/stdio.h [!_ISOMAC && IS_IN (libc)] (fputs): Use
> 	libc_hidden_proto.
> 	* libio/iofputs.c (fputs): Use libc_hidden_weak.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> 
> diff --git a/include/stdio.h b/include/stdio.h
> index 94bc2fd..266c1d2 100644
> --- a/include/stdio.h
> +++ b/include/stdio.h
> @@ -140,6 +140,10 @@ extern int _IO_new_fclose (_IO_FILE*);
>  #   define fclose(fp) _IO_new_fclose (fp)
>  extern int _IO_fputs (const char*, _IO_FILE*);
>  libc_hidden_proto (_IO_fputs)
> +/* The compiler may optimize calls to fprintf into calls to fputs.
> +   Use libc_hidden_proto to ensure that those calls, not redirected by
> +   the fputs macro, also do not go through the PLT.  */
> +libc_hidden_proto (fputs)
>  #   define fputs(str, fp) _IO_fputs (str, fp)
>  extern int _IO_new_fsetpos (_IO_FILE *, const _IO_fpos_t *);
>  #   define fsetpos(fp, posp) _IO_new_fsetpos (fp, posp)
> diff --git a/libio/iofputs.c b/libio/iofputs.c
> index b4fbeb5..176e9ed 100644
> --- a/libio/iofputs.c
> +++ b/libio/iofputs.c
> @@ -43,6 +43,7 @@ _IO_fputs (const char *str, _IO_FILE *fp)
>  libc_hidden_def (_IO_fputs)
>  
>  weak_alias (_IO_fputs, fputs)
> +libc_hidden_weak (fputs)
>  
>  # ifndef _IO_MTSAFE_IO
>  strong_alias (_IO_fputs, __fputs_unlocked)
>