commit 5e27caa60c4ccf257c0dca64883cdf672d8d8ce4 Author: Nick Mathewson nickm@torproject.org Date: Wed Jan 15 10:21:18 2020 -0500

compat_compiler: add a macro to prevent coverity deadcode warnings.

The POSSIBLE(e) macro evaluates to the value of (e), but does so in a way that a static analyzer will not conclude that (e) is impossible. We can use this when we expect our regular compilers to eliminate deadcode, but we don't want coverity to complain about it.

Part of a fix for 32960. --- src/lib/cc/compat_compiler.h | 13 +++++++++++++ 1 file changed, 13 insertions(+)

diff --git a/src/lib/cc/compat_compiler.h b/src/lib/cc/compat_compiler.h index 47782fda0..907622f94 100644 --- a/src/lib/cc/compat_compiler.h +++ b/src/lib/cc/compat_compiler.h @@ -227,4 +227,17 @@ #define EAT_SEMICOLON \ struct dummy_semicolon_eater__

+/** + * Tell our static analysis tool to believe that (clang's scan-build or + * coverity scan) that an expression might be true. We use this to suppress + * dead-code warnings. + **/ +#if defined(__COVERITY__) || defined(__clang_analyzer__) +/* By calling getenv, we force the analyzer not to conclude that 'expr' is + * false. */ +#define POSSIBLE(expr) ((expr) || getenv("STATIC_ANALYZER_DEADCODE_DUMMY_")) +#else +#define POSSIBLE(expr) (expr) +#endif + #endif /* !defined(TOR_COMPAT_COMPILER_H) */