Re: [PATCH] Provide pessimistic defaults for cross compilation tests.

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 20, 2009, 06:50 UTC
Message-ID: <7v63kampwz.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <20090119203400.GA3539@ins.uni-bonn.de>

Ralf Wildenhues <Ralf.Wildenhues@gmx.de> writes:

Show 25 quoted lines

> In a cross compile setup, configure tests that run programs
> cannot be executed; in that case, provide pessimistic default
> values.
>
> Bug reported by Julius Naperkowski.
> ---
>
>> I can post a patch to add sane default settings for AC_RUN_IFELSE in
>> cross compile setups, this weekend.
>
>  configure.ac |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/configure.ac b/configure.ac
> index 363547c..4a208d4 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -360,6 +360,7 @@ AC_RUN_IFELSE(
>  		else if (strcmp(buf, "12345"))
>  		  return 2;]])],
>  	[ac_cv_c_c99_format=yes],
> +	[ac_cv_c_c99_format=no],
>  	[ac_cv_c_c99_format=no])
>  ])
>  if test $ac_cv_c_c99_format = no; then

This one probably is Ok, but...

Show 8 quoted lines

> @@ -380,6 +381,7 @@ AC_RUN_IFELSE(
>  		FILE *f = fopen(".", "r");
>  		return f && fread(&c, 1, 1, f)]])],
>  	[ac_cv_fread_reads_directories=no],
> +	[ac_cv_fread_reads_directories=yes],
>  	[ac_cv_fread_reads_directories=yes])
>  ])
>  if test $ac_cv_fread_reads_directories = yes; then

I am not quite sure if this is an improvement ...

Show 8 quoted lines

> @@ -414,6 +416,7 @@ AC_RUN_IFELSE(
>  		  if (snprintf(buf, 3, "%s", "12345") != 5
>  		      || strcmp(buf, "12")) return 1]])],
>  	[ac_cv_snprintf_returns_bogus=no],
> +	[ac_cv_snprintf_returns_bogus=yes],
>  	[ac_cv_snprintf_returns_bogus=yes])
>  ])
>  if test $ac_cv_snprintf_returns_bogus = yes; then

... nor this one.

Is there a way to say something like "I'll autodetect as much as I can without running tests, but please tell me these characteristics of the target system manually" and leave the resulting config.mak.autogen in a shape that will guarantee compilation failure until the missing ones are supplied by config.mak?

The thing is, I am not convinced that it is desirable to be able to build a possibly suboptimal binary in a cross compilation environment, without being told in what aspect of the resulting binary is suboptimal. I'd rather see a build system that honestly tells me what information it needs but couldn't find, so that I would know I have a chance to help it.

Of course, suggesting a pessimistic default that can result in suboptimal but correct result would be a good thing to help the user help the build. I just think it is a good idea to tell the user we are giving such hint a bit more loudly to draw attention.