问题
In terms of https://blog.mozilla.org/nnethercote/2009/02/27/eliminating-undefined-values-with-valgrind-the-easy-way/
Actually when any actions depend on an earlier jump caused by accessing undefined variables, it reports the same error for those actions.
This sometimes is confusing. For example, I could have an error that depends on an if-check that is far away from here, but the code path indeed depends on that one.
Given a lot of valgrind errors, I am not sure which one to start.
Does valgrind have an option to report 'root-cause'?
回答1:
From the Valgrind documentation:
To see information on the sources of uninitialised data in your program, use the --track-origins=yes option. This makes Memcheck run more slowly, but can make it much easier to track down the root causes of uninitialised value errors.
--track-origins= [default: no]
Controls whether Memcheck tracks the origin of uninitialised values. By default, it does not, which means that although it can tell you that an uninitialised value is being used in a dangerous way, it cannot tell you where the uninitialised value came from. This often makes it difficult to track down the root problem.When set to yes, Memcheck keeps track of the origins of all uninitialised values. Then, when an uninitialised value error is reported, Memcheck will try to show the origin of the value. An origin can be one of the following four places: a heap block, a stack allocation, a client request, or miscellaneous other sources (eg, a call to brk).
For uninitialised values originating from a heap block, Memcheck shows where the block was allocated. For uninitialised values originating from a stack allocation, Memcheck can tell you which function allocated the value, but no more than that -- typically it shows you the source location of the opening brace of the function. So you should carefully check that all of the function's local variables are initialised properly.
Performance overhead: origin tracking is expensive. It halves Memcheck's speed and increases memory use by a minimum of 100MB, and possibly more. Nevertheless it can drastically reduce the effort required to identify the root cause of uninitialised value errors, and so is often a programmer productivity win, despite running more slowly.
Accuracy: Memcheck tracks origins quite accurately. To avoid very large space and time overheads, some approximations are made. It is possible, although unlikely, that Memcheck will report an incorrect origin, or not be able to identify any origin.
Note that the combination --track-origins=yes and --undef-value-errors=no is nonsensical. Memcheck checks for and rejects this combination at startup.
来源：https://stackoverflow.com/questions/35217336/can-valgrind-report-only-the-root-cause-of-reading-uninit-var