On Thu, 18 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/*.
Comments below.
> gcc/ChangeLog
> 2021-11-16 Giuliano Belinassi <gbelina...@suse.de>
>
> * gcc.c (process_command): Skip dumpdir override on -o /dev/null
> or -o /dev/zero.
>
> 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 | 4 +++-
> gcc/gcc.c | 19 +++++++++++++++----
> gcc/testsuite/gcc.dg/devnull-dump.c | 7 +++++++
> 3 files changed, 25 insertions(+), 5 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..4c056606e0c 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -1877,7 +1877,9 @@ 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 @option{-o /dev/null}
> +or @option{-o /dev/zero} is passed to the compiler: on those cases the
> @option{cwd}
> +will be used instead. Options
"It defaults to the location of the output file, unless the output
file is a special file like @code{/dev/null}."
> @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..0173018ac04 100644
> --- a/gcc/gcc.c
> +++ b/gcc/gcc.c
> @@ -5109,10 +5109,21 @@ process_command (unsigned int decoded_options_count,
> {
> free (dumpdir);
> dumpdir = NULL;
> - temp = lbasename (output_file);
> - if (temp != output_file)
> - dumpdir = xstrndup (output_file,
> - strlen (output_file) - strlen (temp));
> + if (strcmp(output_file, "/dev/null") == 0
> + || strcmp(output_file, "/dev/zero") == 0)
Please merge this into the condition of the block and update the comment
/* If -save-temps=obj and -o name, create the prefix to use for %b.
Otherwise just make -save-temps=obj the same as -save-temps=cwd. */
else if (save_temps_flag != SAVE_TEMPS_CWD && output_file != NULL)
please split out
strcmp(output_file, "/dev/null") == 0
|| strcmp(output_file, "/dev/zero") == 0
into a bool special_output_location (const char *) function. For
example on Windows the special output location would be NUL
(appearantly any path ending in NUL works like that - huh).
Note it might be possible to stat() the file and simply behave
this way whenever it exists and is not a regular file. For start
just matching literal /dev/null is good enough IMHO (did you
run into cases with /dev/zero?).
Thanks,
Richard.
> + {
> + /* If output is /dev/null or /dev/zero, we cannot set the dumpdir to
> + /dev/ because no files can be created on that directory. In this
> + case, we do nothing. */
> + }
> + else
> + {
> + /* Set dumpdir as being the same directory where the output file is.
> */
> + temp = lbasename (output_file);
> + if (temp != output_file)
> + dumpdir = xstrndup (output_file,
> + strlen (output_file) - strlen (temp));
> + }
> }
> else if (dumpdir)
> {
> 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;
> +}
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
