On Fri, 19 Nov 2021, Giuliano Belinassi wrote:
> The `configure` scripts generated with autoconf often tests compiler
> features by setting output to `/dev/null`, which then sets the dump
> folder as being /dev/* and the compilation halts with an error because
> GCC cannot create files in /dev/. This is a problem when configure is
> testing for compiler features because it cannot tell if the failure was
> due to unsupported features or any other problem, and disable it even
> if it is working.
>
> As an example, running configure overriding CFLAGS="-fdump-ipa-clones"
> will result in several compiler-features as being disabled because of
> gcc halting with an error creating files in /dev/*.
>
> This commit fixes this issue by checking if the output file is
> /dev/null or /dev/zero. In this case we use the current working
> directory for dump output instead of the directory of the output
> file because we cannot write to /dev/*.
>
> gcc/ChangeLog
> 2021-11-16 Giuliano Belinassi <gbelina...@suse.de>
>
> * gcc.c (process_command): Skip dumpdir override if file is a
> not_actual_file_p.
> (not_actual_file_p): Return true if file is /dev/zero as well.
> * doc/invoke.texi: Update -dumpdir documentation.
>
> gcc/testsuite/ChangeLog
> 2021-11-16 Giuliano Belinassi <gbelina...@suse.de>
>
> * gcc.dg/devnull-dump.c: New.
>
> Signed-off-by: Giuliano Belinassi <gbelina...@suse.de>
> ---
> gcc/doc/invoke.texi | 3 ++-
> gcc/gcc.c | 6 ++++--
> gcc/testsuite/gcc.dg/devnull-dump.c | 7 +++++++
> 3 files changed, 13 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/devnull-dump.c
>
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 6070288856c..4a17cd4d317 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -1877,7 +1877,8 @@ named @file{dir/bar.*}, combining the given
> @var{dumppfx} with the
> default @var{dumpbase} derived from the primary output name. Dump
> outputs also take the input name suffix: @file{dir/bar.c.*}.
>
> -It defaults to the location of the output file; options
> +It defaults to the location of the output file, unless the output
> +file is a special file like @code{/dev/null}. Options
> @option{-save-temps=cwd} and @option{-save-temps=obj} override this
> default, just like an explicit @option{-dumpdir} option. In case
> multiple such options are given, the last one prevails:
> diff --git a/gcc/gcc.c b/gcc/gcc.c
> index 506c2acc282..43d7cde1be9 100644
> --- a/gcc/gcc.c
> +++ b/gcc/gcc.c
> @@ -5098,7 +5098,8 @@ process_command (unsigned int decoded_options_count,
>
> bool explicit_dumpdir = dumpdir;
>
> - if (!save_temps_overrides_dumpdir && explicit_dumpdir)
> + if ((!save_temps_overrides_dumpdir && explicit_dumpdir)
> + || (output_file && not_actual_file_p (output_file)))
> {
> /* Do nothing. */
> }
> @@ -10716,7 +10717,8 @@ static bool
> not_actual_file_p (const char *name)
> {
> return (strcmp (name, "-") == 0
> - || strcmp (name, HOST_BIT_BUCKET) == 0);
> + || strcmp (name, HOST_BIT_BUCKET) == 0
> + || strcmp (name, "/dev/zero") == 0);
> }
OK when you omit the change to include /dev/zero in not_actual_file_p.
Thanks,
Richard.
> /* %:dumps spec function. Take an optional argument that overrides
> diff --git a/gcc/testsuite/gcc.dg/devnull-dump.c
> b/gcc/testsuite/gcc.dg/devnull-dump.c
> new file mode 100644
> index 00000000000..378e0901c28
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/devnull-dump.c
> @@ -0,0 +1,7 @@
> +/* { dg-do assemble } */
> +/* { dg-options "-fdump-ipa-clones -o /dev/null" } */
> +
> +int main()
> +{
> + return 0;
> +}
>
