Hi,

I wanted to debug where my program uses the most memory. (There are no memory leaks, but I want to optimize memory usage on some large inputs. As the code is quite large, simply guessing which part is responsible becomes quite hard :) In the past, I happily used valgrind's massif tool for such job, and it worked like a charm. But now, FPC 2.6.0 with valgrind 3.7.0, it seems valgrind/massif has problems:

$ fpc -gv trivial_alloc.pas
$ valgrind --tool=massif ./trivial_alloc
....
--7286-- VALGRIND INTERNAL ERROR: Valgrind received a signal 11 (SIGSEGV) - exiting
--7286-- si_code=1; Faulting address: 0xFFFFFFF7; sp: 0x6298914c valgrind: the 'impossible' happened:
Killed by fatal signal

(Full output and trivial_alloc.pas attached.)

The code is compiled with -gv option. It works very fine with valgrind's callgrind tool. So I suspect this is a problem with valgrind, specifically massif, not related to FPC. Also, it seems to fail the same way with older/newer FPC versions (I tried 2.2.4, 2.4.4, 2.6.0, and 2.7.1 from today 2012-05-11). Probably, some valgrind version broke massif for FPC binaries.

So, questions:

1. I want to report this as massif's bug. Any ideas what more information should I provide to valgrind's developers? I don't know if they are familiar with FPC. And simple C examples work fine, so it's probably something specific in FPC binaries.

- Maybe this problem is already reported?

- Maybe there's a workaround? IOW, can someone successfully use massif with FPC programs?

2. Is there any other reliable memory profiler for FPC? As you can swap memory manager in Pascal, and FPC can give you a backtrace, I suppose it's quite possible to just write a unit that works between your program and standard memory manager, and tracks memory usage this way. This will only measure memory use of Pascal code (external libs don't go through FPC memory manager), but that would be very fine for me --- I know (well, I'm 99% sure) that my Pascal code is the main memory eater here.

I didn't find any (good and maintained) memory profiler mentioned on http://wiki.lazarus.freepascal.org/Profiling#Memory_Profiling . (I tried FpProfiler, but it depends on inserting instrumentation code into Pascal sources. That's actually a very nice idea, but it means it's closely tied to what fcl-passrc can handle. And current fcl-passrc still lacks a couple of features (reported). Also FpProfiler seems to use an older, local fcl-passrc version.)

Thanks,
Michalis

You could try whether heaptrc is of any help for you (see here: http://www.freepascal.org/docs-html/rtl/heaptrc/usage.html ). If not it might at least provide a starting point if you should decide to write a custom memory profiler. Otherwise I don't know of any FPC based memory profilers.

Regards,
Sven

This is known problem not related to fpc. Run

valgrind --tool=massif --run-libc-freeres=no ./trivial_alloc

Ludo

Thanks. I'm using HeapTrc all the time, that's how I know that my program has no memory leaks and that's how I know FPC memory manager can be reliably switched and a backtrace for each allocation can be captured :)

My needs are a little larger than what HeapTrc currently does, I want a memory profiler --- where you can see at a glance what is the largest memory consumer inside your code and such. Things like http://lazarusroad.blogspot.com/2007/09/zlibar-memory-behavior-compressing-many.html . Like calling HeapTrc.DumpHeap all the time, and tracking where the large increases happened. Valgrind+massif used to be very helpful for this.

Michalis

Fantastic, many thanks, it works like a charm now! :) Both on trivial tests, as well as my large 3D viewer (view3dscene). Thank you! Oh, and I see this hint was just added to the
http://wiki.lazarus.freepascal.org/Profiling too.

Michalis