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author | Rupert Swarbrick <rswarbrick@lowrisc.org> | 2020-02-27 13:20:41 +0000 |
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committer | Rupert Swarbrick <rswarbrick@lowrisc.org> | 2020-02-27 13:43:58 +0000 |
commit | 2efea60720650c57649aec6ceef1756b892eec9b (patch) | |
tree | 9ad49487b943fdb3908f26fdf73de705c997141f /ax_append_flag.m4 | |
parent | 157143b5038ef2b92b1c70d445b566d57b6f5096 (diff) | |
download | riscv-isa-sim-2efea60720650c57649aec6ceef1756b892eec9b.zip riscv-isa-sim-2efea60720650c57649aec6ceef1756b892eec9b.tar.gz riscv-isa-sim-2efea60720650c57649aec6ceef1756b892eec9b.tar.bz2 |
Allow overriding CFLAGS and similar when building
Before this patch, I don't think it was possible to change (say)
CFLAGS as part of running the make command. Nor did setting them when
running configure do anything. Getting this right is a little fiddly:
for example, see Automake's approach at [1] ("AM_CFLAGS" and friends).
This patch adds an "mcppbs-" prefix, and sets things up properly for
CFLAGS, CPPFLAGS, CXXFLAGS and LDFLAGS. Note that the bulk of the
patch is either the auto-generated configure script or the ax_*.m4
files vendored in from the autoconf archive (needed to handle
--export-dynamic correctly without trashing settings from the user
running configure).
What's supposed to happen is as follows:
- Base compilation flags that should apply to everything (standard
optimisation flags, warning flags etc.) are defined in
Makefile.in.
- When the user runs configure, they can set compilation flags on
the command line. These end up as environment variables in the
shell script.
- Compilation flags that can only be decided when we run
configure (this is currently just whether we support
-Wl,--export-dynamic) are appended to the configure-time LDFLAGS
environment variable.
- At the end of the configure script, these environment variables
are spliced into Makefile.in to fill out the corresponding
@<varname>@ entries.
- When running make, the user might again override compilation
flags. These will get appended to the flags found so far.
As a concrete example:
mkdir build
cd build
../configure CXXFLAGS='-O3'
make CXXFLAGS='-O0'
will result in c++ compile commands that look like this:
g++ -MMD -MP \
-DPREFIX=\"/usr/local\" -Wall -Wno-unused -g -O2 -std=c++11 \
-O3 \
-O0 \
-I. -I.. -I../fesvr -I../riscv -I../dummy_rocc -I../softfloat \
-I../spike_main -fPIC -c ../fesvr/elfloader.cc
(I've added some newlines to wrap the long line).
Note that we have the base flags from Makefile.in (called
$(default-CXXFLAGS) there) first. Then we have the -O3 from the
configure command. Finally we have the -O0 from the Make command line.
And I can finally run "make CXXFLAGS='-O0 -g3'". Phew!
[1] https://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
Diffstat (limited to 'ax_append_flag.m4')
-rw-r--r-- | ax_append_flag.m4 | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/ax_append_flag.m4 b/ax_append_flag.m4 new file mode 100644 index 0000000..dd6d8b6 --- /dev/null +++ b/ax_append_flag.m4 @@ -0,0 +1,50 @@ +# =========================================================================== +# https://www.gnu.org/software/autoconf-archive/ax_append_flag.html +# =========================================================================== +# +# SYNOPSIS +# +# AX_APPEND_FLAG(FLAG, [FLAGS-VARIABLE]) +# +# DESCRIPTION +# +# FLAG is appended to the FLAGS-VARIABLE shell variable, with a space +# added in between. +# +# If FLAGS-VARIABLE is not specified, the current language's flags (e.g. +# CFLAGS) is used. FLAGS-VARIABLE is not changed if it already contains +# FLAG. If FLAGS-VARIABLE is unset in the shell, it is set to exactly +# FLAG. +# +# NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. +# +# LICENSE +# +# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de> +# Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com> +# +# Copying and distribution of this file, with or without modification, are +# permitted in any medium without royalty provided the copyright notice +# and this notice are preserved. This file is offered as-is, without any +# warranty. + +#serial 8 + +AC_DEFUN([AX_APPEND_FLAG], +[dnl +AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_SET_IF +AS_VAR_PUSHDEF([FLAGS], [m4_default($2,_AC_LANG_PREFIX[FLAGS])]) +AS_VAR_SET_IF(FLAGS,[ + AS_CASE([" AS_VAR_GET(FLAGS) "], + [*" $1 "*], [AC_RUN_LOG([: FLAGS already contains $1])], + [ + AS_VAR_APPEND(FLAGS,[" $1"]) + AC_RUN_LOG([: FLAGS="$FLAGS"]) + ]) + ], + [ + AS_VAR_SET(FLAGS,[$1]) + AC_RUN_LOG([: FLAGS="$FLAGS"]) + ]) +AS_VAR_POPDEF([FLAGS])dnl +])dnl AX_APPEND_FLAG |