[LLVMdev] Looking for a fix to memory leak in DWARF support

[Sergei Larin]

David,

  This certainly looks relevant - even if this is not the ultimate cause of the issue. I will try it. Thank you. 

  ...it also sounds very reasonable what Eric is describing:

" It's just an explosion of debug info because of our lack of uniquing for type information." 

It looks more like the version of tools I am dealing with was never ready to handle LTO + debug efficiently, and it would be more like back porting a major new feature to an older codebase :(  This sure looks like a fun project... Maybe my time will be better used to convince the customer to upgrade :)

Thanks again for helping.

Sergei

---
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation


> -----Original Message-----
> From: David Blaikie [mailto:dblaikie at gmail.com]
> Sent: Friday, June 13, 2014 4:32 PM
> To: Sergei Larin
> Cc: LLVM Developers Mailing List
> Subject: Re: Looking for a fix to memory leak in DWARF support
> 
> On Fri, Jun 13, 2014 at 11:03 AM, Sergei Larin <slarin at codeaurora.org> wrote:
> >
> > David,
> >
> > Thanks for the quick response...
> >
> >
> > No, at this point I am just getting into the issue... I assume it is a leak, but
> no clear proof yet. I was hoping it was an obvious thing since I recall a
> discussion about it a while ago... but maybe I am just confused.
> 
> There have been some memory leaks fixed - the discussion you might be
> recalling is the frontend leaks using DIBuilder. Addressed by changes like this:
> http://llvm.org/viewvc/llvm-project?rev=208055&view=rev
> 
> But I don't think that was ever a crippling bug, so far as I recall.
> We only found this when using leak detectors - not when compiling vast
> swathes of code, etc.
> 
> > Was your work for compressing DWARF data  motivated by a certain
> inefficiency in debug info representation? Did it result in significant savings?
> 
> compressing DWARF has little to do with memory leaks, etc - it's related to
> the nature of DWARF on disk, that's where the compression occurs (in the
> object (and dwo) files themselves). Yes, it does have substantial savings,
> though I don't have the numbers at hand right now. (string sections
> especially are compressed well).
> 
> - David
> 
> >
> > Thanks.
> >
> > Sergei
> >
> > ---
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> > hosted by The Linux Foundation
> >
> >
> >> -----Original Message-----
> >> From: David Blaikie [mailto:dblaikie at gmail.com]
> >> Sent: Friday, June 13, 2014 12:41 PM
> >> To: Sergei Larin
> >> Cc: LLVM Developers Mailing List
> >> Subject: Re: Looking for a fix to memory leak in DWARF support
> >>
> >> Are you sure it's a leak, not just a large memory footprint?
> >>
> >> A lot of things have changed. Heck, even the bugs that we've fixed
> >> might not have existed two years ago (I've certainly created (and
> >> fixed) my share of bugs in debug info).
> >>
> >> Best you start with a leak tracking tool and at least be able to
> >> point to the major leak culprit (eg: "90% of the leaked memory was
> >> allocated at <stack
> >> trace>")
> >>
> >> On Fri, Jun 13, 2014 at 9:16 AM, Sergei Larin <slarin at codeaurora.org>
> wrote:
> >> >
> >> > David, (and everyone else)
> >> >
> >> >   I am forced to do some maintenance work on a fairly old LLVM
> >> > branch (likely based on release 3.1) that among other issues has a
> >> > major problem with memory leak somewhere around DWARF debug
> support.
> >> > In fact customer is unable to build with -g at all - simply running
> >> > out of memory on their project...
> >> >
> >> >   I seem to remember that there has been a major fix related to it,
> >> > but finding it hard to pinpoint. So the appeal to the communal
> >> > memory
> >> > - do you remember if  there was a single fix (since the middle of
> >> > 2012 or so) that would have addressed such issue?
> >> >
> >> >   I know the code was drastically change since - I have seen this
> >> > for instance
> >> > llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?
> >> > vie
> >> > w=log&
> >> > pathrev=205990
> >> >
> >> > ...but not sure this is what I am looking for, and whether there is
> >> > something less drastic than I can do to plug that leak.
> >> >
> >> > Any clue would be very much appreciated.
> >> >
> >> > Thanks.
> >> >
> >> > Sergei
> >> >
> >> > ---
> >> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> >> > hosted by The Linux Foundation
> >> >
> >