I use a C++ library for an iOS app. With Apple LLVM 3.1 compiler configured (default), I get a lot of warnings for this C++ code, most of them saying:
... is a GNU extension
The introduction of clang's user manual says:
The Clang driver and language features are intentionally designed to be as compatible with the GNU GCC compiler as reasonably possible, easing migration from GCC to Clang. In most cases, code "just works".
So, is it save to just look for a switch to disable this warnings (btw. how to?) or should I better get this lib rid of all GNU extensions?
You can suppress the warnings using compiler flags. Clang tells you which compiler flag to use for each warning. After a build, choose View > Navigators > Show Log Navigator. Then choose the latest build log from the log navigator. Find a file with a warning and click the disclosure button at the right end of its status line. Xcode will show you the compiler command line and output for that file. Each warning should include the compiler flag that enables the warning. Example:
In my example, the warning flag is -Wpointer-arith. So the warning can be disabled by -Wno-pointer-arith. So I could add that flag to the “Other Warning Flags” build setting:
Related
I'm using Clang 3.8 to compile one file that comes from a different source in a project. This is a temporary crutch, as this file is an addition to a library that I also use, and the code it has will be part of that library's next release. However, these people develop with less stringent warning flags than I do.
I'm not interested in these warnings as they're benign, I don't maintain that file, and it'll go away within a few months. Of course, I can selectively remove a warning or two, but I think that it makes more sense in this case to disable all and every warnings that it generates because I could change the warning settings of my project later and more occurrences could come out of it.
I've tried #pragma clang diagnostic ignored "-Weverything", but Clang warns that -Weverything is an unknown warning group.
How can I ask Clang to not generate any warnings for that file?
Indeed, the "-Weverything" is not a group of warnings, but just a special option passed to the compiler. Here is code that handles this case: lib/Basic/Warnings.cpp:118
You still can compile your problematic source file using slightly different rules/flags as you use for others sources:
clang -Wno-everything foo.c
However, I'd recommend to disable each warning explicitly using #pragma.
In case you disable all warnings, and then upgrade your compiler, then you may miss some new warnings, which could be important (e.g. undefined behaviour checks, security checks, etc).
Also, imagine what happens if the file is not gone after three months, but stays in the project forever.
If you need your compiler flags to be consistent between GCC and Clang, they both have the -w flag:
$ clang --help | grep -i suppress
-w Suppress all warnings
I know there are many compiler flags and how to use them. At times while seeing a third-party code we encounter a new flag and fail to understand why the hell this flag is used? How no warnings are shown even though there is retain-cycle in an existing code.
So I tried to find if I can find all the compiler flags with description. That would help to understand about its usage and other flags to replace it.
Please provide me some link or list of all the flags.
The list of compiler flags I found it in Clang Compiler User Manual.
This link may get broken some day but surely it will be there with the Compiler User Manaul.
Command Line Options
This section is generally an index into other sections. It does not go
into depth on the ones that are covered by other sections. However,
the first part introduces the language selection and other high level
options like -c, -g, etc.
Options to Control Error and Warning Messages
-Werror Turn warnings into errors.
-Werror=foo
Turn warning “foo” into an error.
-Wno-error=foo Turn warning “foo” into an warning even if -Werror is specified.
-Wfoo Enable warning “foo”.
-Wno-foo Disable warning “foo”.
-w Disable all diagnostics.
-Weverything Enable all diagnostics.
-pedantic Warn on language extensions.
-pedantic-errors
.....Continued
I am having no luck the last few days since Xcode 5.1 came out.
I keep getting this error on an old project that supports iOS 6.0:
ERROR:
clang: error: unknown argument: '-fno-obj-arc' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
Command /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang failed with exit code 1
There are not many posts about this on the internet and some suggestions seem to be to change your CFLAGS but I have no idea how to do that in Xcode.
Apple suggests this from their documents:
Compiler
As of Apple LLVM compiler version 5.1 (clang-502) and later, the
optimization level -O4 no longer implies link time optimization (LTO).
In order to build with LTO explicitly use the -flto option in addition
to the optimization level flag. (15633276) The Apple LLVM compiler in
Xcode 5.1 treats unrecognized command-line options as errors. This
issue has been seen when building both Python native extensions and
Ruby Gems, where some invalid compiler options are currently
specified. Projects using invalid compiler options will need to be
changed to remove those options. To help ease that transition, the
compiler will temporarily accept an option to downgrade the error to a
warning:
-Wno-error=unused-command-line-argument-hard-error-in-future
Note: This option will not be supported in the future. To workaround
this issue, set the ARCHFLAGS environment variable to downgrade the
error to a warning. For example, you can install a Python native
extension with:
$ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future easy_install ExtensionName
Similarly, you can install a Ruby Gem with:
$ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future gem install GemName 16214764 updated
How do I get this workaround? Obviously Apple has messed up because it should only be presenting me with a warning and not an error according to their documents.
Any help would be greatly appreciated. I can not build my app until this issue is rectified.
There is no such thing as -fno-obj-arc. This never was working correctly; you just weren't seeing the warnings. The correct form is -fno-objc-arc.
EDIT (appended info drawn from my comments below): This is not a clang error. It is an error in the project; clang is merely reporting it. The project itself wrongly contains the -fno-obj-arc argument, probably in the Compile Sources build phase of the target (as described here: How can I disable ARC for a single file in a project?). It is easy to type the setting incorrectly; what has changed in Xcode 5.1 is merely that clang is now calling the problem to your attention. Thus, as I said before, this never was working correctly; you presumably intended to turn off ARC for certain files, but you were failing to do so, as the build argument was incorrectly entered.
Update to xcode now throws unknown compiler flags as hard errors rather than warnings. Found this to be helpful:
https://langui.sh/2014/03/10/wunused-command-line-argument-hard-error-in-future-is-a-harsh-mistress/
I figured out with a small bit of help from matt.
I was trying to figure out where to change the -fno-obj-arc and NO ONE answered that question.
I found this link to be helpful...
http://blog.evanmulawski.com/?p=36
Once you select build phases and compile sources, you can look next to the files in your project and change their build flags.
Thanks for the attempt guys.
export ARCHFLAGS="-Wno-error=unused-command-line-argument-hard-error-in-future"
You need to change -fno-obj-arc to -fno-objc-arc.
Select project -> targets -> build phases ..see picture
Address-Sanitizer https://code.google.com/p/address-sanitizer/wiki/AddressSanitizer
I have compile my own llvm (pretty straight forward compiling) because apple's llvm not support this function.
I have tested the clang for mac command line program, it works (but without showing the line the sourcecode).
for iOS, there is still some problems:
compile simulator version : report error for pre-compiled header:
In file included from /Users/fluke/Documents/projects/tmp/testAsanNoARC/testAsanNoARC/testAsanNoARC-Prefix.pch:12:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIKit.h:9:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIAccelerometer.h:53:24: error: 'UIAccelerometer' is unavailable: not available on OS X
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration NS_DEPRECATED_IOS(2_0, 5_0);
^
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIAccelerometer.h:33:12: note: declaration has been explicitly marked unavailable here
#interface UIAccelerometer : NSObject {
^
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIAccelerometer.h:53:71: error: 'UIAcceleration' is unavailable: not available on OS X
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration NS_DEPRECATED_IOS(2_0, 5_0);
...
compile for device version, it reports lack of libarc (but actually I don't enable ARC)
ld: file not found: /Users/fluke/Documents/tools/asan/Debug+Asserts/lib/arc/libarclite_iphoneos.a
clang: error: linker command failed with exit code 1 (use -v to see invocation)
so I try use it for a separate lib - just new a lib target and use my own clang while the main target still use apple's llvm. the program compiles ( may need to link to the asan dylib in the built llvm), but not work because I asan need to be loaded before our program entry.
who have experience with doing this?
I finally get the asan work for me with my friend's help.
move all c/c++ code to a new target (cocoa lib target) of xcode project. make the project build and run normally as it was a single app before separate c/c++ codes to a lib.
build llvm. ref http://blog.wadetregaskis.com/tot-clang-llvm-in-xcode/
add a clang option to xcode. for convenient you can use this template: http://blog.wadetregaskis.com/tot-clang-llvm-in-xcode/ . change clang path to the clang just build in the previous step.
change the lib target in the xcode to use the new clang/llvm, add a cflag -fsanitize=address. then build, if some api (such as opengl/system video function) is reported not supported, then you can put it into the app project, your clang doesn't support compiling it.
if you pass the compile, it will report linkage problem of __asan_xxx function, add a lib called "libclang_rt.asan_osx_dynamic.dylib" to the app's linkage dependency, and it's located in your llvm's
./Debug+Asserts/lib/clang/3.4/lib/darwin/ folder.
then you need to specified the out put file or else the report will goes to the stdout with color characters which will confuse you. put this lines into your main.m:
extern void __sanitizer_set_report_path(const char *path);
__sanitizer_set_report_path("/tmp/asan.txt");
then you can make your program some memory error such as use after free or heap buffer overflow. the asan will let the program crash in the first error, with /tmp/asan.txt.number report generated.
you're almost there, the report show's the error stack with the file's offset. all you need to do is one more step - resolve the address to code line. you need to find the DWARF file of your project, then use a tool called asan_symbolize.py to generate the new report with source code line. you can goole asan_symbolize.py then get and fix this script to use the DWARF file. you can find the DWARF file by right click your production app, select show in finder, then to up a level to get the iphone simulator directory, open the bundle called your.app.dSYM, then you can get the DWARF in ./Content/Resources/DWARF.
The only thing that I haven't list here is the modified asan_symbolize.py, you can modify it by your self, it has no magic, you just correct some path and it will work.
The errors listed in the original post have little to do with ASan itself. Most certainly you would've got them without the -fsanitize=address flag.
Building and running for iOS isn't supported yet, however you can build an app targeting the iOS simulator - it should work just fine.
Please don't hesitate to direct further questions to address-sanitizer#googlegroups.com
I have a chunk of code that crashes unless I build with optimizations off. I'm building with LLVM compiler 2.0
I would like to turn off optimizations by wrapping the offending code with a #pragma compiler directive; or turn off optimizations for an entire file.
I've been digging in the clang manual and code; but nothing jumps out at me.
Does anyone know how to change the optimizations for a single CU (as opposed to for the entire app)?
You can set per-file compiler flags in Xcode. In Xcode 4 (which I assume you're using because of the LLVM 2.0 reference), first select the project in the left-hand project browser. Go to the Build Phases tab and expand the Compile Sources build phase.
In there, you can set per-file compiler flags, so you could try going to the offending file and entering in -O0 as a flag to try and disable optimizations for just that file.
GCC has some attributes you can set for this, as pointed out by Johannes in his answer here, but these might not be in LLVM. Also, from the comments there, it appears that these are not even in Apple's customized GCC used for building iOS applications.