[sr #110387] Document better where to put -m32 or -m64 compiler options

[Bruno Haible]

URL:
  <https://savannah.gnu.org/support/?110387>

                 Summary: Document better where to put -m32 or -m64 compiler
options
                 Project: Autoconf
            Submitted by: haible
            Submitted on: Tue 01 Dec 2020 11:00:50 PM CET
                Category: None
                Priority: 5 - Normal
                Severity: 3 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
        Operating System: None

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Details:

The section about CFLAGS in section "Preset Output Variables"
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Preset-Output-Variables.html
was written in 2006, see
https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=63b0709b9482f1a282d584239d3bcb016633d7cf
.

This text considers the habits of Makefile authors and of Automake, when to
use CC with CFLAGS and CPPFLAGS (namely for preprocessing and compiling to
object files) vs. CC with CFLAGS and LDFLAGS (namely for linking).

However, another use of CC is in config.guess, when the user has not provided
a --host option. Here, at least nowadays, CC is used without CFLAGS, CPPFLAGS,
nor LDFLAGS.

This variable is used on GNU/Linux, Solaris, HP-UX systems to determine
whether the build produces 32-bit or 64-bit binaries, and sets the host_cpu
portion of the config.guess result accordingly. See
https://lists.gnu.org/archive/html/config-patches/2018-12/msg00012.html .

When users put -m32 or -m64 options into variables other than CC, this
detection does not work and causes problems thereafter. See
https://lists.gnu.org/archive/html/bug-gnulib/2020-12/msg00012.html for an
example.

Find attached a patch to the Autoconf documentation, to make it clear that
-m32 or -m64 options need to go into CC.




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File Attachments:


-------------------------------------------------------
Date: Tue 01 Dec 2020 11:00:50 PM CET  Name:
0001-Document-better-where-to-put-m32-or-m64-compiler-opt.patch  Size: 2KiB  
By: haible

<http://savannah.gnu.org/support/download.php?file_id=50370>

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