URL:
<https://savannah.gnu.org/bugs/?63310>
Summary: configure: unexpected CPPFLAGS effect on C compiler
options check
Project: make
Submitter: pexu
Submitted: Thu 03 Nov 2022 01:47:46 PM UTC
Severity: 3 - Normal
Item Group: Bug
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Component Version: 4.4
Operating System: Any
Fixed Release: None
Triage Status: None
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Follow-up Comments:
-------------------------------------------------------
Date: Thu 03 Nov 2022 01:47:46 PM UTC By: Pekka S <pexu>
Hi.
In order to determine the warning flags that the C compiler supports configure
for GNU make 4.4 (lines 7887...7966) currently preprocesses ($CC -E) a stub
program, then discards any lines that begin with `#' (grep -v) and finally
picks up all remaining words.
Here's an excerpt from the `conftest.c' that is fed to C preprocessor:
7937: #if __GNUC__ + (__GNUC_MINOR__ >= 9) > 4 || (__clang_major__ +
(__clang_minor__ >= 9) > 3)
7938: -Wno-float-conversion
7938: #endif
The expected preprocessed source might then look like:
# 0 "<command-line>" 2
# 1 "conftest.c"
# 2 "conftest.c"
-Wno-float-conversion
The issue here is that the user might pass in CPPFLAGS (or CFLAGS, for that
matter), say `-include header.h', that cause additional preprocessed output.
In that case unfortunately all output from these unexpected sources
(statements and such) is added to GL_CFLAG_GNULIB_WARNINGS as well, likely
causing problems downstream.
The difficulty here is that there is no good way of detecting (as it stands
now) that `confest.c' is being preprocessed. The least problematic might be
to check `#if __has_include(<confest.c>) /* ... */'.
One possibility to overcome this would be to use e.g. sed or awk. Change the
interesting lines to e.g. ``#pragma MAKE GL_CFLAG_GNULIB_WARNINGS
"-Wno-float-conversion"'' and pick up the inresting part,
`-Wno-float-conversion', with a suitable regular expression pattern. This way
the output should be also more inline with C standard (unless there's some
compiler that is really picky about unknown pragmas at early stages).
Of course, the super easy way is just to use `grep --
^[[:space:]]*-W[[:alpha:]][[:alpha:]-]*' instead of the current negative form.
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