Re: [perf top] annotation doesn't work, libunwind doesn't seem to be working either

[Namhyung Kim <namhyung@kernel.org>]

Hi Ingo,

On Fri, Apr 04, 2025 at 11:41:46AM +0200, Ingo Molnar wrote:
> 
> BTW., here's a few other 'perf' annoyances I have, if anyone's 
> listening :-)

Thanks for the report.  Glad to hear from you.

> 
> 
> 1)
> 
> I cannot get the libunwind build-feature failure to go away:
> 
> ...                               libcrypto: [ on  ]
> ...                               libunwind: [ OFF ]
> ...                             libcapstone: [ on  ]
> ...                               llvm-perf: [ on  ]
> 
> I do have libunwind-dev installed:
> 
> ii  libunwind-dev:amd64                                         1.6.2-3.1                                           amd64        library to determine the call-chain of a program - development
> ii  libunwind8:amd64                                            1.6.2-3.1                                           amd64        library to determine the call-chain of a program - runtime
> 
> but it fails to link:
> 
>  kepler:~/tip/tools/build/feature> cat test-libunwind.make.output
>  /usr/bin/ld: /tmp/cc2BfaNM.o: in function `main':
>  test-libunwind.c:(.text+0x1c): undefined reference to `_Ux86_64_create_addr_space'
>  /usr/bin/ld: test-libunwind.c:(.text+0x44): undefined reference to `_Ux86_64_init_remote'
>  /usr/bin/ld: test-libunwind.c:(.text+0x6b): undefined reference to `_Ux86_64_dwarf_search_unwind_table'
>  collect2: error: ld returned 1 exit status
> 
> I tried to install the libunwind-19-dev package, I tried to 
> uninstall/reinstall - no combination seems to work.
> 
> perf is also totally unhelpful about resolving such issues - it used to 
> issue tips about what packages to install, but those tips are not 
> present anymore, for this one at least.

Since v6.13, we switched to disable libunwind by default and used
unwinding in libdw.

commit 13e17c9ff491 ("perf build: Make libunwind opt-in rather than opt-out")

You need to pass LIBUNWIND=1 to build with it.

> 
> 2)
> 
> More annoyingly, I cannot get source code annotation of the kernel to 
> work - this might be related to the libunwind build failure (or not).

I don't think it's related.  Anyway do you see the same for user
binaries or is it only for the kernel?

> 
> Within 'perf top' I go into a function, and I press 's', which is 
> supposed to toggle the source code annotation ... but nothing happens.
> 
> 'nothing happens' is perhaps the most passive-aggressive reaction a 
> tool can give to a user. I'd prefer a *crash* to ignoring the keypress 
> ...

Oh ok.  I prefer a warning. :)

> 
> There's no error printed anywhere - just the color of the hexadecimal 
> labels changes, nothing else.
> 
> 'perf top' won't annotate kernel functions (despite me having a 
> DEBUGINFO kernel package installed and booted), nor will it even 
> annotate its own functions within 'perf', in a similar fashion.

I see.  So the problem is not specific to the kernel.

> 
> It's similar for 'perf report' too, although that's not a surprise, 
> they share much of the codebase.

Yep, of course.

> 
> 'perf annotate --stdio' only shows an objdump --disassemble style 
> output, but without any source annotations either.
> 
> This is a rather frustrating user experience. :-/

Sorry about that.  I suspect that I made a mistake when I was working on
the data type profiling.  I'll take a look.

Thanks,
Namhyung