howto debug memory errors using valgrind+garbage collector

[jakobkroeker]

we should figure out, how to debug memory errors using valgrind+garbage collector,
or is it possible to disable gc?

(recall the bug in ColumnRankProfile, see
https://groups.google.com/forum/#!topic/ffpack-devel/2mwmhJpvQQ4
)
somewhat useful:
GC_DONT_GC environment flag

another helpful way is replacing GC_MALLOC with malloc
using LD_PRELOAD
e.g.

with malloc.c:

#include <stdio.h>
#include <stdlib.h>

void * GC_malloc(size_t a)
{
 // printf("calling my malloc\n");
  return malloc(a);
}

gcc -fPIC -shared malloc.c -o libmygc.so

export LD_PRELOAD = ./libmygc.so

[mikestillman]

In order for the e/unit-tests to not use gc (so that valgrind will detect more issues), what is needed?

1. remove calls to GC_MALLOC, etc. in M2mem-replacement.c
2. flint needs to be compiled without gc support
3. use of finalizers in e directory: these functions should be made into no ops.
4. remove -lgc from the included libraries
5. remember to add libraries to LD_LIBRARY_PATH (add libraries/final/lib to this list)
6. initialize factory correctly? (Is something needed here: need to check this)
7. what else?

[mahrud]

With new changes to GC, would be good to document debugging memory issues. One way I've tried is using Flamegraphs: http://www.brendangregg.com/FlameGraphs/memoryflamegraphs.html