What does valgrind still reachable mean?

The “still reachable” category within Valgrind’s leak report refers to allocations that fit only the first definition of “memory leak”. These blocks were not freed, but they could have been freed (if the programmer had wanted to) because the program still was keeping track of pointers to those memory blocks.

What does still reachable mean?

In short: “definitely lost” means your program is leaking memory — fix those leaks! “still reachable” means your program is probably ok — it didn’t free some memory it could have. This is quite common and often reasonable. Don’t use –show-reachable=yes if you don’t want to see these reports.

How do I fix valgrind error?

Table of Contents

1. General tips. Solve the first error. Look for function names and line numbers. Look for the last point in the stack trace where your program appears.
2. Common types of Valgrind errors. Invalid reads and invalid writes. Uninitialized value errors. Memory leaks. Forgetting to deallocate things you allocated.

What is possibly lost in valgrind?

possibly lost: heap-allocated memory that was never freed to which valgrind cannot be sure whether there is a pointer or not. still reachable: heap-allocated memory that was never freed to which the program still has a pointer at exit.

Is still reachable a memory leak?

“definitely lost” means your program is leaking memory — fix it! “possibly lost” means your program is probably leaking memory, unless you’re doing funny things with pointers. “still reachable” means your program is probably ok — it didn’t free some memory it could have. This is quite common and often reasonable.

Is Valgrind ever wrong?

3 Answers. Yes, there are false positives with Valgrind, that’s why it has suppression files for particular glibc and gcc versions, for example. The false positives may arise if you are using older valgrind with newer gcc and glibc, i.e., valgrind 3.3 with glibc 2.9.

Do Valgrind errors matter?

Memory errors versus memory leaks Valgrind reports on both with equal vigor, but please don’t you conflate errors with leaks or assume them equally important. When a program dynamically allocates memory and forgets to later free it, it creates a leak.

How do I enable Valgrind?

To run Valgrind, pass the executable as an argument (along with any parameters to the program). The flags are, in short: –leak-check=full : “each individual leak will be shown in detail” –show-leak-kinds=all : Show all of “definite, indirect, possible, reachable” leak kinds in the “full” report.

Where is the memory leak in JNI?

The only way to discover JNI memory leaks is to use a heap-dump tool that explicitly marks native references. If possible, you should not use any global references. It’s better to assign the desired object to the field of a normal Java class.

Why is Valgrind so slow?

According to Valgrind Manual, Valgrind will very noticeably slow down your application: The amount of instrumentation code added varies widely between tools. At one end of the scale, Memcheck adds code to check every memory access and every value computed, making it run 10-50 times slower than natively.

How do you reduce Valgrind?

How to make a suppression file. Run valgrind as usual, but with the extra option –gen-suppressions=all. This tells valgrind to print a suppression after every error it finds.

What does still reachable mean in C-Valgrind?

Memory marked by Valgrind as “still reachable” is memory that is: 1 Allocated by your program at some point. 2 Not freed before the program exit. 3 Still pointed to by some variable at program exit (this is what “reachable” means). More

When does a memory leak occur in Valgrind?

Valgrind is a program that checks for both memory leaks and runtime errors. A memory leak occurs whenever you allocate memory using keywords like new or malloc, without subsequently deleting or freeing that memory before the program exits.

When does a runtime error occur in Valgrind?

Valgrind is a program that checks for both memory leaks and runtime errors. A memory leak occurs whenever you allocate memory using keywords like new or malloc, without subsequently deleting or freeing that memory before the program exits. Runtime errors, as their name implies, are errors that occur while your program is running.

What does the stack trace in Valgrind mean?

In the middle of running my code, Valgrind discovered a runtime error, in this case, Invalid write of size 4. Notice that it gives us a “stack trace”, in other words, a list of which functions were called to get to the point where this error occurred.