The project that I am trying to build has default flags
CFLAGS = -Wall -g -O2
CXXFLAGS = -g -O2
I need to append a flag -w to both these variables (to remove: 'consider all warnings as errors')
I have a method to work it out, give
make 'CFLAGS=-Wall -g -O2 -w'; 'CXXFLAGS=-g -O2 -w'
OR
Run ./configure and statically modify Makefile
But I want to append my options with the existing options while running configure or make
The post
Where to add a CFLAG, such as -std=gnu99, into an autotools project
conveniently uses a macro to achieve this.
You almost have it right; why did you add the semicolon?
To do it on the configure line:
./configure CFLAGS='-g -O2 -w' CXXFLAGS='-g -O2 -w'
To do it on the make line:
make CFLAGS='-g -O2 -w' CXXFLAGS='-g -O2 -w'
However, that doesn't really remove consider all warnings as errors; that removes all warnings. So specifying both -Wall and -w doesn't make sense. If you want to keep the warnings but not have them considered errors, use the -Wall -Wno-error flags.
Alternatively, most configure scripts which enable -Werror by default also have a flag such as --disable-werror or similar. Run ./configure --help and see if there's something like that.
Related
I have a simple project with a simple configure.ac script:
AC_INIT(...)
AM_INIT_AUTOMAKE([-Wall -Werror foreign])
AC_PROG_CC
AC_CONFIG_HEADERS([config.h])
AC_CONFIG_FILES(...)
AC_OUTPUT
using GNU Autoconf version 2.69 (OpenSUSE Linux with gcc 9.2.1), but gcc is being called with no warning flags:
gcc -DHAVE_CONFIG_H -I. -I.. -g -O2 -MT aprog.o -MD -MP -MF .deps/aprog.Tpo -c -o aprog.o aprog.c
mv ...
gcc -g -O2 -o aprog aprog.o -lgmp
In particular, I found -Wformat not working. Shouldn't -Wall include -Wformat? And shouldn't all warnings appear on the make line? If I run gcc line directly with -Wformat the warning shows in compile but it doesn't when I run autoconf, configure and make.
What I'm doing wrong?
The -Wall flag in the AM_INIT_AUTOMAKE(...) invocation refers to warnings from automake and related tools like aclocal, not to compiler warnings. You will see these warnings when you are running autoreconf.
Note that while you can also add -Werror to AM_INIT_AUTOMAKE(...) to make your autoreconf run fail on warnings, many common macros (like those shipped with gettext or libtool) will still use deprecated macros which generates a warning, so -Werror means you cannot use this standard set of tools, so -Werror is not very useful in many cases.
If you want to add compiler options, there are a third party macros (e.g. AX_CHECK_COMPILE_FLAG) which test whether the compiler recognizes a given compile option and you can then add them to some variable and use that in places. That is a different stackoverflow question, though.
I have the following in my GNU makefile:
# CXXFLAGS ?= -DNDEBUG -g2 -O3
CXXFLAGS ?=
# Add -DNDEBUG if nothing specified
ifeq ($(filter -DDEBUG -DNDEBUG,$(CXXFLAGS)),)
$(info Adding -DNDEBUG to CXXFLAGS)
CXXFLAGS += -DNDEBUG
endif
# Add a symolize if nothing specified
ifeq ($(filter -g -g1 -g2 -g3 -Oz,$(CXXFLAGS)),)
$(info Adding -g2 to CXXFLAGS)
CXXFLAGS += -g2
endif
# Add an optimize if nothing specified
$(info Adding -O3 to CXXFLAGS)
ifeq ($(filter -O -O0 -O1 -O2 -O3 -Og -Os -Oz -Ofast,$(CXXFLAGS)),)
CXXFLAGS += -O3
endif
When I run it:
$ make CXXFLAGS="-g3"
Adding -DNDEBUG to CXXFLAGS
Adding -O3 to CXXFLAGS
g++ -g3 -c foo.cpp
...
In fact, if I uncomment the CXXFLAGS ?= -DNDEBUG ..., then I can append again. But that's not very helpful since I'm trying to make arguments optional (but with sane defaults).
And if I type just make, then it works (-fPIC -march=native -Wall -Wextra -pipe is added later by the same makefile, and it has always worked):
$ make
Adding -DNDEBUG to CXXFLAGS
Adding -g2 to CXXFLAGS
Adding -O3 to CXXFLAGS
g++ -DNDEBUG -g2 -O3 -fPIC -march=native -Wall -Wextra -pipe -c serpent.cpp
...
According to the manual and 6.6 Appending More Text to Variables:
Often it is useful to add more text to the value of a variable already defined. You do this with a line containing ‘+=’, like this:
objects += another.o
Why is make not adding the values to the variable? How can I achieve the behavior I want?
By passing a variable via command-line, you're telling make that you are overriding any definitions in the file, which allows a user to compile as they intend rather than as you intend. Ignoring the restriction of user freedom, you can use the override directive:
To append more text to a variable defined on the command line, use:
override variable += more text
Variable assignments marked with the override flag have a higher priority
than all other assignments, except another override. Subsequent
assignments or appends to this variable which are not marked override
will be ignored.
I would discourage you from using override when possible because it's annoying to realize that -O0 was needed to disable the optimizations that you enabled when I don't want them enabled (after all, I specify my own flags for a reason). Of course, if no flags were specified at all, then defaults are perfectly reasonable. In fact, Automake projects seem to default to -g -O2 when no compilation flags are specified.
There are exceptions to this advice of course, such as adding a directory to search for includes/libs or preprocessor definitions for compiling a conditional section of code on a certain platform.
Under GNUStep on Arch Linux, I'm running into an interesting error on a fresh install.
Using my build system I run
gcc `gnustep-config --debug-flags` [other command line args]
in order to build up the command line per the operating system's necessary flags.
This works fine under Ubuntu, but on Arch Linux I'm getting a rather random error:
/usr/include/features.h:328:4: error: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Werror=cpp]
Well, gnustep-config --debug-flags spits out the following:
-MMD -MP -D_FORTIFY_SOURCE=2 -DGNUSTEP -DGNUSTEP_BASE_LIBRARY=1 -DGNU_GUI_LIBRARY=1 -DGNU_RUNTIME=1 -DGNUSTEP_BASE_LIBRARY=1 -fno-strict-aliasing -pthread -fPIC -g -DDEBUG -fno-omit-frame-pointer -Wall -DGSWARN -DGSDIAGNOSE -Wno-import -march=x86-64 -mtune=generic -pipe -fstack-protector-strong --param=ssp-buffer-size=4 -fgnu-runtime -fconstant-string-class=NSConstantString -fexec-charset=UTF-8 -I. -I/home/qix/GNUstep/Library/Headers -I/usr/include -D_FORTIFY_SOURCE=2 -I/usr/include -I/usr/include -I/usr/include -I/usr/lib/libffi-3.1/include/ -I/usr/lib/libffi-3.1/include -I/usr/include/libxml2 -I/usr/include/p11-kit-1
As well, I wish not to have optimizations on my debug builds (and later on I even override GNUStep's -g parameter to -g2).
Is there a way to explicitly undefine -D_FORTIFY_SOURCE later on in the command line, after the call to gnustep-config?
For example, something like
gcc `gnustep-config --debug-flags` -U_FORTIFY_SOURCE ...
where the -U undefines the previously defined macro?
Something to mention; I have -Werror enabled on purpose, and I'd like to keep it.
For now, using sed to work around this works. It appears this is a known issue with _FORTIFY_SOURCE causing issues, and there isn't a straightforward fix.
`gnustep-config --debug-flags | sed 's/-D_FORTIFY_SOURCE=2//g'`
I'm following Zed Shaw's tutorial "Learn C the Hard Way" and trying to teach myself c programming language.
On my ubuntu desktop, I encountered the linking problem he mentioned in the note of this post.
That is, when linking a static library with gcc, using a command like this:
gcc -Wall -g -DNDEBUG -lmylib ex29.c -o ex29
The linker fails to find the functions in the lib. To link correctly, I have to change the order of source file and lib to this:
gcc -Wall -g -DNDEBUG ex29.c -lmylib -o ex29
And I'm trying to use the makefile offered by Zed to automate unit test. The makefile looks like this:
TEST_SRC=$(wildcard tests/*_tests.c)
TESTS=$(patsubst %.c,%,$(TEST_SRC))
TARGET=build/libYOUR_LIBRARY.a
tests: CFLAGS += $(TARGET)
tests: $(TESTS)
sh ./tests/runtests.sh
The rest part of the makefile that isn't listed here can build the $(TARGET) lib flawlessly.
The problem is Zed append the lib to the $(CFLAGS) and use the implicit rule to compile the test files which leads to a command like this:
gcc -g -O2 -Wall -Wextra -Isrc -rdynamic -DNDEBUG tests/hashmap_tests.c build/mylib.a -o tests/list_tests
The command fails because of the link problem mentioned before as expected.
The solution I came up with was to write the compilation command explicitly like this so I can change the order:
$(TESTS): $(TARGET)
$(CC) $(CFLAGS) $^ $(TARGET) -o $#
This works fine if there is only one main source file. Unfortunately, I have several out there under the ./tests directory, and a command like this is a total disaster.
My question is, how should I change my makefile to make it work or is there any other way I can do the same work as elegant as expected?
CFLAGS holds compiler flags, like -g -O2. You should not add linker flags to it. CPPFLAGS holds preprocessor flags like -Isrc -DNDEBUG. LDFLAGS holds linker flags, which would include things like -L (capital L) if you need it to find libraries, and -rdynamic. And the LDLIBS variable holds libraries, so you should do this:
CPPFLAGS = -Isrc -DNDEBUG
CFLAGS = -g -O2 -Wall -Wextra
LDFLAGS = -rdynamic
LDLIBS = -lmylib
Now you can use the built-in rules for GNU make to build your program. You can see a list of the build-in rules by running make -p -f/dev/null.
Of course the above are just the default variables make defines and uses with its default rules. You don't have to use them, but in general it's better to follow conventions rather than flaunt them.
I am trying to run program from the Learn C Hard Way book
I need to pass the library filename 'build/liblcthw.a' as the last parameter.
For eg :
Doesnt Work on Ubuntu :
gcc -g -O2 -Wall -Wextra -Isrc -rdynamic -DNDEBUG build/liblcthw.a tests/list_tests.c -o tests/list_tests
Works on Ubuntu :
gcc -g -O2 -Wall -Wextra -Isrc -rdynamic -DNDEBUG tests/list_tests.c -o tests/list_tests build/liblcthw.a
How do I handle this in Makefile ? CFLAGS will only add it before the source filename and it doesnt work. How do I force CFALGS to add the library filename at the end of the command ?
CFLAGS are flags for the C compiler. Libraries typically go into a variable called LDLIBS. Set LDLIBS=build/liblcthw.a and see if that works.
The first invocation doesn't succeed because the order of sources and libraries in the command line is wrong. The correct order is source files, then object files, followed by static libraries followed by dynamic libraries.