clang static analyser undefined value in boost/libs/filesystem/src/unique_path.cpp

[Niall Douglas]

Assigned value is garbage or undefined at line 131.

Please ​https://ci.nedprod.com/job/Boost.AFIO%20Static%20Analysis%20Pre-Check/112/clangScanBuildBugs/? for more detail.

[anonymous]

It is obviously used right below on lines 132 and 133. Line 132 shifts it 4 bits to the right if nibbles_used is odd. Then it's lower nibble is set to s[i] on line 133.

[viboes]

Replying to anonymous:

It is obviously used right below on lines 132 and 133. Line 132 shifts it 4 bits to the right if nibbles_used is odd. Then it's lower nibble is set to s[i] on line 133.

The code uses ran[0] unassigned.

[Niall Douglas]

The analyser sees this possibility:

char ran[16]; nibbles_used=32; c=ran[nibbles_used/2];

Do you see the undefined behaviour now? ran shouldn't be read from ran[16].

Niall

[Niall Douglas]

New information: I upgraded the static analyser to use clang 3.4 which is greatly improved. Now this report in filesystem is the ONLY static analysis failure reported for AFIO's use of Boost.

See ​https://ci.nedprod.com/view/All/job/Boost.AFIO%20Static%20Analysis%20Pre-Check/lastSuccessfulBuild/clangScanBuildBugs/

Niall

[Niall Douglas]

This bug is still being reported by the clang 3.4 static analyser in the forthcoming Boost 1.56 beta. It would be really nice if this got fixed.

Niall