Commit 387cfcce authored by Nick Mathewson's avatar Nick Mathewson 🐚
Browse files

Add a coccinelle script to look for {inc,dec}rements in log_debug 

We want to forbid this pattern since, unlike the other log_*()
macros, log_debug() conditionally evaluates its arguments only if
debug-level logging is enabled.  Thus, a call to
    log_debug("%d", x++);
will only increment x if debugging logs are enabled, which is
probably not what the programmer intended.

One bug caused by this pattern was #30628.

This script detects log_debug( ) calls with any of E++, E--, ++E,
or --E in their arguments, where E is an arbitrary expression.

Closes ticket 30743.
parent 41261c3b

changes/ticket30743

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  o Minor features (maintenance scripts):

    - Add a coccinelle script to detect bugs caused by incrementing or

      decrementing a variable inside a call to log_debug().  Since

      log_debug() is a macro whose arguments are conditionally evaluated, it

      is usually an error to do this. One such bug was 30628, in which SENDME

      cells were miscounted by a decrement operator inside a log_debug()

      call.  Closes ticket 30743.

scripts/coccinelle/debugmm.cocci

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// Look for use of expressions with side-effects inside of debug logs.

//

// This script detects expressions like ++E, --E, E++, and E-- inside of

// calls to log_debug().

//

// The log_debug() macro exits early if debug logging is not enabled,

// potentially causing problems if its arguments have side-effects.



@@

expression E;

@@

*log_debug(... , <+...  --E ...+>, ... );





@@

expression E;

@@

*log_debug(... , <+...  ++E ...+>, ... );



@@

expression E;

@@

*log_debug(... , <+...  E-- ...+>, ... );





@@

expression E;

@@

*log_debug(... , <+...  E++ ...+>, ... );