Bug#879003: diffoscope: objdump --line-numbers makes diffoscope *very* slow

[Mike Hommey]

On Thu, Oct 19, 2017 at 08:50:19AM +0900, Mike Hommey wrote:
> On Wed, Oct 18, 2017 at 07:29:52PM +0900, Mike Hommey wrote:
> > Package: diffoscope
> > Version: 87
> > Severity: normal
> > 
> > Dear Maintainer,
> > 
> > Today I was comparing firefox builds from mozilla CI with diffoscope,
> > and it was taking an awful lot of time. Quick inspection revealed that
> > this is largely due to objdump --line-numbers. Remove --line-numbers
> > from the objdump command line created in ObjdumpDisassembleSection makes
> > a huge difference:
> > 
> > $ time diffoscope --html diff.html firefox{1,2}.tar.bz2 # unpatched
> > real	58m48.870s
> > user	62m41.966s
> > sys	3m3.710s
> > 
> > $ time diffoscope --html diff.html firefox{1,2}.tar.bz2 # patched
> > real	7m19.159s
> > user	7m42.558s
> > sys	3m2.730s
> 
> Some timings, fwiw:
> 
> $ time objdump --disassemble --demangle --section=.text libxul.so > /dev/null
> 
> real	0m23.431s
> user	0m23.366s
> sys	0m0.064s
> 
> $ time objdump --line-numbers --disassemble --demangle --section=.text libxul.so > /dev/null
> 
> real	25m49.537s
> user	25m49.191s
> sys	0m0.308s

FWIW:

$ llvm-objdump-4.0 --disassemble --section=.text libxul.so > /dev/null

real	0m8.992s
user	0m8.854s
sys	0m0.112s

$ time llvm-objdump-4.0 --line-numbers --disassemble --section=.text libxul.so > /dev/null

real	0m19.738s
user	0m19.461s
sys	0m0.120s

(on the same file as above, not actually containing debug info)

but it doesn't support --demangle. Also, its --disassemble output has
some formatting issues.

Versions before 4.0 didn't support --line-numbers.

Mike