Valgrind "Conditional jump or move depends on uninitialised value(s)" Error

8
votes

I am getting many errors with valgrind saying "Conditional jump or move depends on uninitialized value(s)".

Below is the one of the blocks. All of them are similar:

vasm_sourceline_info_t* line = asmState->firstLine;
if (line == NULL) return;
while ((line = line->next) != NULL)
{
   printf ("[%s(%i)] %s\n", line->fileName, line->lineNumber, line->data);
}

The error itself is on the while() line. vasm_sourceline_info is a doubly linked list structure. The code ~works~ but this error is worrying. Is there something else in code stomping on memory, or is the above function flawed in some way?

2
clinked-listvalgrind
are all the next pointers initialized? - CodesInChaos
You know you would think that would be the FIRST thing I would look at... No, although I take care in the add/remove/append logic, the initialization function did NOT set next/prev to NULL... Problem solved. Thanks! - Tim Sarbin
it happens or me too in valid code sometimes. - Johannes Schaub - litb
valgrind.org/docs/manual/mc-manual.html#mc-manual.uninitvals - Collin Price

2 Answers

14
votes

Compile with optimizations OFF (-O0). Run valgrind with --track-origins=yes to determine the source of the errors. See here for more.

6
votes

There's nothing wrong with the code per se, but if one of the lines' next field has not been initialized (presumably the last line's next field), that would explain the message.