Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler #15292

hebasto · 2019-01-30T11:39:03Z

#14711 introduced some warnings when building with gcc compiler.

See:

Remove uses of chainActive and mapBlockIndex in wallet code #14711 (comment) by @laanwj
Remove uses of chainActive and mapBlockIndex in wallet code #14711 (review) by @ryanofsky

This gcc issue has been known since version 4.6.0 and last updated in 2017.
From the boost docs:

The default constructor of optional creates an uninitialized optional object.

Also: False positive with -Wmaybe-uninitialized (pointed out by @Empact)

This PR removes these warnings.

cc: @Empact @practicalswift

DrahtBot · 2019-01-30T12:14:22Z

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Conflicts

No conflicts as of last run.

maflcko · 2019-01-30T13:41:10Z

Generally we don't work around bugs in a compiler if they are only warning related and fixed in recent versions.

hebasto · 2019-01-30T13:44:57Z

@MarcoFalke

Generally we don't work around bugs in a compiler if they are only warning related and fixed in recent versions.

Which recent version of gcc do you mean?

maflcko · 2019-01-30T14:41:33Z

According to the bug report, it was fixed in gcc6. I am using clang7.

ryanofsky · 2019-01-30T15:29:11Z

I would prefer not to make these changes since I think they make the code less readable, are only applicable to older buggy versions of gcc, and just avoid warnings not errors.

But I will add my utACK 595b62f since the changes do look safe, and other people might want them.

I wonder what would happen if you tried to replace:

Optional<int> height;

with:

Optional<int> height = nullopt;

I think a change like that would be more readable.

hebasto · 2019-01-30T17:09:30Z

@MarcoFalke

According to the bug report, it was fixed in gcc6. I am using clang7.

I am using gcc 7.3.0 (both Linux Mint 19.1 and Ubuntu Bionic). Warnings are still present.

@ryanofsky

Optional<int> height = nullopt;

I've tried this approach while working on this PR. nullopt did not help. Perhaps this is due to the lazy initialization inside boost::optional.

maflcko · 2019-01-30T17:13:00Z

gcc8 will also spit out a false positive warning, since it can not infer that either none or both of altheight and height are initialized. Not sure if this should be fixed or how.

Empact · 2019-01-30T18:51:18Z

I think "The default constructor of optional creates an uninitialized optional object." may be misleading as default-constructed values are valid, e.g.. boost::optional has an is_initialized member that is false on default initialization, and just means the object is falsey.

Other thoughts:
I would prefer not to use auto here given there are plenty of numeric types.
I would access this functionality via src/optional.h, where the other boost::optional references are.

Incidentally here's the doc where boost recommends this fix.
No opinion on whether this should be fixed.

hebasto · 2019-01-30T18:57:11Z

@Empact TIL. Thank you.

hebasto · 2019-01-30T19:12:19Z

@Empact your comment has been addressed.

laanwj · 2019-01-30T19:31:13Z

I'm using gcc 7.3.0 on my main development system so I see these scary warnings all the time, so I'd prefer for this to be merged or the relevant warning disabled (for that gcc).

Edit: tested that this makes the warnings disappear here.

laanwj · 2019-01-30T19:33:05Z

src/wallet/rpcwallet.cpp

@@ -41,6 +41,8 @@

 #include <functional>

+#include <boost/optional.hpp>


I'd mildly prefer to redirect this through our optional.h, define our own make_optional like the Option<T> itself instead of boost appearing here direclty.

gmaxwell · 2019-01-30T19:55:33Z

Found this PR after seeing the scary warnings... maybe-uninitialized is a pretty potent warning, I wouldn't want to disable it unless it was only on old compilers.

maflcko · 2019-01-30T20:03:16Z

Hmm, one of the warnings disappears when going from gcc7 to gcc8?

practicalswift · 2019-01-30T20:28:49Z

utACK c14d580 modulo @laanwj's nit regarding optional.h

hebasto · 2019-01-30T20:46:45Z

@laanwj's nit has been addressed.

practicalswift · 2019-01-30T20:54:09Z

utACK 2d48314

laanwj · 2019-01-30T21:43:49Z

utACK 2d48314

Empact · 2019-01-30T22:07:10Z

utACK 2d48314

@laanwj

…-uninitialized warnings on GCC compiler 2d48314 Remove 'boost::optional'-related gcc warnings (Hennadii Stepanov) Pull request description: #14711 introduced some warnings when building with gcc compiler. See: - #14711 (comment) by @laanwj - #14711 (review) by @ryanofsky This gcc [issue](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47679) has been known since version 4.6.0 and last updated in 2017. From the boost [docs](https://www.boost.org/doc/libs/1_69_0/libs/optional/doc/html/boost_optional/quick_start/optional_automatic_variables.html): > The default constructor of `optional` creates an _uninitialized_ `optional` object. Also: [False positive with -Wmaybe-uninitialized](https://www.boost.org/doc/libs/1_69_0/libs/optional/doc/html/boost_optional/tutorial/gotchas/false_positive_with__wmaybe_uninitialized.html) ([pointed out](#15292 (comment)) by @Empact) This PR removes these warnings. cc: @Empact @practicalswift Tree-SHA512: 752ae3c3ca6282bbf98726236fbc3069ab9d1aee57ae2ec2668b32e4541e7bc1acb15b7d6fa9e2b6daf1ec29c0987a1053ee1ca0f523b71367ff911221c58c94

e9434ee Remove false positive GCC warning (Hennadii Stepanov) Pull request description: On master (f05c1ac) GCC compiler fires a false positive `-Wmaybe-uninitialized`: ``` wallet/wallet.cpp: In static member function ‘static std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(interfaces::Chain&, const WalletLocation&, std::__cxx11::string&, std::vector<std::__cxx11::basic_string<char> >&, uint64_t)’: wallet/wallet.cpp:3913:27: warning: ‘*((void*)& time_first_key +8)’ may be used uninitialized in this function [-Wmaybe-uninitialized] Optional<int64_t> time_first_key; ^~~~~~~~~~~~~~ ``` The same as #15292. This PR leverages a workaround and removes the warning. ACKs for top commit: laanwj: ACK e9434ee, removes the warning for me (gcc 7.4.0) kristapsk: ACK e9434ee Tree-SHA512: 8820a8ba6a75aa6b1ac675a38c883a77f12968b010533b6383180aa66e7e0d570bf6300744903ead91cf9084e5345144959cd6b0cea1b763190b8dd49bacce75

e9434ee Remove false positive GCC warning (Hennadii Stepanov) Pull request description: On master (f05c1ac) GCC compiler fires a false positive `-Wmaybe-uninitialized`: ``` wallet/wallet.cpp: In static member function ‘static std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(interfaces::Chain&, const WalletLocation&, std::__cxx11::string&, std::vector<std::__cxx11::basic_string<char> >&, uint64_t)’: wallet/wallet.cpp:3913:27: warning: ‘*((void*)& time_first_key +8)’ may be used uninitialized in this function [-Wmaybe-uninitialized] Optional<int64_t> time_first_key; ^~~~~~~~~~~~~~ ``` The same as bitcoin#15292. This PR leverages a workaround and removes the warning. ACKs for top commit: laanwj: ACK e9434ee, removes the warning for me (gcc 7.4.0) kristapsk: ACK e9434ee Tree-SHA512: 8820a8ba6a75aa6b1ac675a38c883a77f12968b010533b6383180aa66e7e0d570bf6300744903ead91cf9084e5345144959cd6b0cea1b763190b8dd49bacce75

Summary: Backport of core [[bitcoin/bitcoin#15292 | PR15292]]. Test Plan: With GCC: ninja check Make sure the warnings are gone (tested with GCC 7.5). Reviewers: #bitcoin_abc, deadalnix Reviewed By: #bitcoin_abc, deadalnix Differential Revision: https://reviews.bitcoinabc.org/D5696

Summary --- While compiling on Gitian using GCC 7 (and locally using GCC 8) we have observed that there are various warnings related to uninitialized values being used -- these warnings are false positives. After auditing the code it is clear to me that they are not real uninitialized usages. GCC's static checker gets confused by the rather complex code that ends up unitializing these values. This commit fixes that issue. Backport status --- This is a backport of core #15292: - bitcoin/bitcoin#15292 Original commit message: Remove 'boost::optional'-related gcc warnings Test Plan --- - `ninja all check-all` No behavioral or other changes were introduced. This is a purely cosmetic warning-suppression commit. Even the "uninitialized" values are now "initialized" to the identical default thing with this commit.

e9434ee Remove false positive GCC warning (Hennadii Stepanov) Pull request description: On master (f05c1ac) GCC compiler fires a false positive `-Wmaybe-uninitialized`: ``` wallet/wallet.cpp: In static member function ‘static std::shared_ptr<CWallet> CWallet::CreateWalletFromFile(interfaces::Chain&, const WalletLocation&, std::__cxx11::string&, std::vector<std::__cxx11::basic_string<char> >&, uint64_t)’: wallet/wallet.cpp:3913:27: warning: ‘*((void*)& time_first_key +8)’ may be used uninitialized in this function [-Wmaybe-uninitialized] Optional<int64_t> time_first_key; ^~~~~~~~~~~~~~ ``` The same as bitcoin#15292. This PR leverages a workaround and removes the warning. ACKs for top commit: laanwj: ACK e9434ee, removes the warning for me (gcc 7.4.0) kristapsk: ACK e9434ee Tree-SHA512: 8820a8ba6a75aa6b1ac675a38c883a77f12968b010533b6383180aa66e7e0d570bf6300744903ead91cf9084e5345144959cd6b0cea1b763190b8dd49bacce75

fanquake added Wallet Refactoring labels Jan 30, 2019

hebasto force-pushed the 20190130-gcc-maybeuninitialized branch from a1d9961 to 595b62f Compare January 30, 2019 11:49

hebasto force-pushed the 20190130-gcc-maybeuninitialized branch from 595b62f to c14d580 Compare January 30, 2019 19:10

hebasto changed the title ~~Remove 'boost::optional'-related gcc warnings~~ Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler Jan 30, 2019

laanwj reviewed Jan 30, 2019

View reviewed changes

Remove 'boost::optional'-related gcc warnings

2d48314

hebasto force-pushed the 20190130-gcc-maybeuninitialized branch from c14d580 to 2d48314 Compare January 30, 2019 20:45

laanwj merged commit 2d48314 into bitcoin:master Jan 30, 2019

hebasto deleted the 20190130-gcc-maybeuninitialized branch January 30, 2019 22:50

hebasto mentioned this pull request Feb 1, 2020

Remove false positive GCC warning #18052

Merged

hebasto mentioned this pull request Mar 20, 2020

wallet: Remove calls to Chain::Lock methods #17954

Merged

hebasto mentioned this pull request Nov 15, 2020

Silence false positive GCC warning in wallet/rpcwallet.cpp #20386

Merged

bitcoin locked as resolved and limited conversation to collaborators Dec 16, 2021

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler #15292

Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler #15292

hebasto commented Jan 30, 2019 •

edited

Loading

DrahtBot commented Jan 30, 2019 •

edited

Loading

maflcko commented Jan 30, 2019

hebasto commented Jan 30, 2019

maflcko commented Jan 30, 2019

ryanofsky commented Jan 30, 2019

hebasto commented Jan 30, 2019 •

edited

Loading

maflcko commented Jan 30, 2019

Empact commented Jan 30, 2019 •

edited

Loading

hebasto commented Jan 30, 2019

hebasto commented Jan 30, 2019

laanwj commented Jan 30, 2019 •

edited

Loading

laanwj Jan 30, 2019

gmaxwell commented Jan 30, 2019

maflcko commented Jan 30, 2019

practicalswift commented Jan 30, 2019

hebasto commented Jan 30, 2019

practicalswift commented Jan 30, 2019

laanwj commented Jan 30, 2019

Empact commented Jan 30, 2019

		@@ -41,6 +41,8 @@

		#include <functional>

		#include <boost/optional.hpp>

Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler #15292

Remove 'boost::optional'-related false positive -Wmaybe-uninitialized warnings on GCC compiler #15292

Conversation

hebasto commented Jan 30, 2019 • edited Loading

DrahtBot commented Jan 30, 2019 • edited Loading

Conflicts

maflcko commented Jan 30, 2019

hebasto commented Jan 30, 2019

maflcko commented Jan 30, 2019

ryanofsky commented Jan 30, 2019

hebasto commented Jan 30, 2019 • edited Loading

maflcko commented Jan 30, 2019

Empact commented Jan 30, 2019 • edited Loading

hebasto commented Jan 30, 2019

hebasto commented Jan 30, 2019

laanwj commented Jan 30, 2019 • edited Loading

laanwj Jan 30, 2019

Choose a reason for hiding this comment

gmaxwell commented Jan 30, 2019

maflcko commented Jan 30, 2019

practicalswift commented Jan 30, 2019

hebasto commented Jan 30, 2019

practicalswift commented Jan 30, 2019

laanwj commented Jan 30, 2019

Empact commented Jan 30, 2019

hebasto commented Jan 30, 2019 •

edited

Loading

DrahtBot commented Jan 30, 2019 •

edited

Loading

hebasto commented Jan 30, 2019 •

edited

Loading

Empact commented Jan 30, 2019 •

edited

Loading

laanwj commented Jan 30, 2019 •

edited

Loading