How to detect thread sanitizer for gcc 5

Question

How can I detect whether thread sanitizer has been turned on for a build using gcc 5? Neither one of the two between __has_feature(thread_sanitizer) nor __SANITIZE_THREAD__ work

#include <iostream>

using std::cout;
using std::endl;

int main() {
    cout << __has_feature(thread_sanitizer) << endl;
    cout << __SANITIZE_THREAD__ << endl;
}

https://wandbox.org/permlink/t5qYme4Whyj54aYV. This compiles on the versions of clang that have thread sanitizer; but not for some gcc versions (5 in particular)

Both the feature check and the __SANITIZE_THREAD__ macro are useful in detecting when the thread sanitizer has been turned on so tests can suppress false-negatives (eg. when thread sanitizer catches a bug that's not actually a data race) See this for more

Regarding the close vote: how can I make the question clearer? — Curious, Aug 14 '19 at 18:15
@JesperJuhl TSAN does not instrument some things correctly in the older gcc-based versions. Eg. inline assembly — Curious, Aug 14 '19 at 18:19
@LightnessRacesinOrbit I'm not sure what you mean, isn't there just one meaning for "detecting" in this context? Similar to https://en.cppreference.com/w/cpp/feature_test? — Curious, Aug 14 '19 at 18:21
"TSAN does not instrument some things correctly in the older gcc-based versions" - Isn't the solution then to just use *newer* gcc versions (which may also bring other benefits)? — Jesper Juhl, Aug 14 '19 at 18:22
What I'm saying is you did not tell us what sort of outcome you want. Do you need a macro? A variable? A function call? A command-line utility? What? — Lightness Races in Orbit, Aug 14 '19 at 18:22
@JesperJuhl I would, but some libraries that we support rely can't yet migrate to the newer versions of the compiler since the targetted client code uses the older version — Curious, Aug 14 '19 at 18:23
@LightnessRacesinOrbit Not quite sure what it means to be binary-safe in this context, but I can't really control when everyone using the library upgrades their compiler. Nor can I do it myself — Curious, Aug 14 '19 at 18:26
@LightnessRacesinOrbit I see; the build model for this library is not the typical "distribute binary and include headers" one that you might be talking about (correct me if I am wrong). It gets included and built from scratch along with the client code. — Curious, Aug 14 '19 at 18:35
@LightnessRacesinOrbit I didn't even consider binary compatibility? You bought it up no? What am I missing? I just need the library code to compile and run without error on older compiler versions (which is why I need the feature check macro) — Curious, Aug 14 '19 at 18:41

Wyck · Accepted Answer · 2019-08-14T18:47:15.280

4

I don't know, but as a last resort, the following command line will find a #define if it exists:

diff <(gcc -dM -E -x c /dev/null) <(gcc -fsanitize=thread -dM -E -x c /dev/null)

On my gcc 7.4.0 it outputs:

> #define __SANITIZE_THREAD__ 1

...which means that __SANITIZE_THREAD__ is defined to be 1 if you are using -fsanitize=thread, but is not defined if you don't. So you should guard your code behind an #ifdef __SANITIZE_THREAD__ rather than just using the symbol directly.

Additional Info:

I checked the gcc source and the __SANITIZE_THREAD__ macro was not introduced until version 7.1.0.

edited Aug 14 '19 at 18:47

answered Aug 14 '19 at 18:31

Wyck

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It isn't a last resort, it comes not long after checking the doc. Sadly, in this case, with gcc-5, the output is empty. – Marc Glisse Aug 14 '19 at 18:33
Could you explain how this command works? And what it's doing? Curious :) – Curious Aug 14 '19 at 18:47
1

@Curious `-E` invokes the preprocessor and sends the output to stdout. `-dM` displays defined macros (requires `-E` to be specified). `-x c` forces compilation as a C file. (you could alternatively use `-x c++`) and finally `/dev/null` sets the input file to `/dev/null` (nothing). Then it diffs this preprocessor output with and without the `-fsanitize=thread` flag. – Wyck Aug 14 '19 at 18:57

How to detect thread sanitizer for gcc 5

1 Answers1

Additional Info:

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