Re: Shark is losing source code
Re: Shark is losing source code
- Subject: Re: Shark is losing source code
- From: kwiley <email@hidden>
- Date: Fri, 6 Jun 2008 10:44:06 -0700
On Jun 5, 2008, at 5:56 PM, Rick Altherr wrote:
On Jun 5, 2008, at 4:06 PM, kwiley wrote:
Is this the right group to post Shark questions to?
My code was built with -O -g -DNDEBUG, although note that I have
the exact same problem if I build with -g alone.
I run my executable with Shark, wait for it, and get the typical
Shark results. I double-click various rows in the profile view to
see the associated code. Now, the weird part is that for *some*
files it shows the code, but for others it only shows the
assembly. If I look at the build transcript, the files in question
were definitely built with -g.
This is a rather peculiar build I admit, because it is an external
target that invokes make and basically doesn't use Xcode for much
other than editing, but nevertheless, what's going on?
I realize this post probably isn't sufficient to solve the problem,
but does anyone know how I should start working on this? I don't
really have any ideas?
Thanks.
-g in Xcode 3 uses DWARF for debugging, but in an effort to reduce
binary size, it leaves the DWARF information in the
intermediate .o's. When shark looks at the executable, it finds a
set of debug information that basically says "function a, which is
at this address, has debug info in /foo/a.o". To help uniquely
identify the .o's, the filesystem timestamp for the .o is also
encoded in the binary.
What does this mean to you? If the .o's are deleted, Shark can't
read the debug info from them. If the .o's are moved to a different
folder, Shark can't find it. If the .o's are modified after the
compile, Shark won't use it. If you strip debug information on the
main executable, Shark won't know which .o's to look in. Lastly,
there is a bug in Shark 4.5 where the wrong timestamp is used when
validating a .o that was aggregated into a .a before being linked
into the final executable. That bug has been fixed internally and
will be incorporated into our next release.
As a workaround, you can use dsymutil to generate a .dSYM file.
The .dSYM is essentially an aggregation of all the debug information
contained in the .o's. If you generate one successfully and place
it in the same folder as the executable, Shark will automatically
read the debug information from the .dSYM. This can be used to work
around the .a bug in Shark.
--
Rick Altherr
Architecture and Performance Group
email@hidden
Hmmm, well, I appreciate all the detailed information. However, I
don't think I've done anything wonky like moving or deleting .o files
or stripping debug info out of the executable. I just build from
Xcode and go straight to Start With Performance Tool and Shark it. I
also don't think there is any .o to .a aggregation going on, so, I'm a
little confused about what the problem could be. Is there any chance
Shark simply doesn't know *where* the .o files are. They are, of
course, not in the same directory (by a long shot) as the executable.
The install target (remember I'm building with a standard makefile
with an External Target in Xcode, although I build with Xcode's Build
command instead of on the command line), puts the executable in a
totally different directory.
The funniest thing is, as I said, Shark show source for some
functions, but not others. I find that totally perplexing.
I'll look into dsymutil. "which" found it, so I just need to see how
to use it now. Thanks much.
Cheers!
________________________________________________________________________
Keith Wiley email@hidden http://www.cs.unm.edu/~kwiley
"Yet mark his perfect self-contentment, and hence learn his lesson, that
to be self-contented is to be vile and ignorant, and that to aspire is
better than to be blindly and impotently happy."
-- Edwin A. Abbott,
Flatland
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