Boost C++ Libraries: Ticket #8954: clang static analyser undefined value in boost/libs/filesystem/src/unique_path.cpp

anonymous — Sat, 07 Sep 2013 20:05:01 GMT

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 — Tue, 08 Oct 2013 17:39:58 GMT

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 — Mon, 28 Oct 2013 15:50:06 GMT

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 — Mon, 27 Jan 2014 19:13:45 GMT

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 — Mon, 28 Jul 2014 10:23:18 GMT

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