[llvm-dev] Slow debugger starts of LLVM tools

[Petr Penzin via llvm-dev]

I've ran into the same issue before. I tend to see it as a price we pay 
for static linking, since it brings all the symbols debugger has to read 
at the start time. Quick check on launching a tool (fort) in GDB (I 
usually use it) and LLDB shows that LLDB starts much faster, but takes 
time to set breakpoints and launch the application, so I think they are 
roughly on the same page in terms of delays.

-Petr

On 1/9/19 6:17 PM, Zachary Turner via llvm-dev wrote:
> This is admittedly a longshot, but Can you check whether you 
> experience unusually long run times with LLDB? If there’s something 
> strange about tge binaries we generate, maybe lldb will exhibit some 
> strangeness too and we can more easily profile it.
> On Wed, Jan 9, 2019 at 2:48 PM Shoaib Meenai via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     I don't know about the issues with running being slow, but using a
>     GDB index greatly speeds up initial symbol loading. Compile with
>     `-ggnu-pubnames` and link with `-Xlinker --gdb-index` and you
>     should get significantly faster symbol load times. (I'd be curious
>     to see if it helps with the issues with run being slow as well.)
>
>     On 1/9/19, 2:07 PM, "llvm-dev on behalf of David Greene via
>     llvm-dev" <llvm-dev-bounces at lists.llvm.org
>     <mailto:llvm-dev-bounces at lists.llvm.org> on behalf of
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>
>         David Jones via llvm-dev <llvm-dev at lists.llvm.org
>     <mailto:llvm-dev at lists.llvm.org>> writes:
>
>         > GDB likes to load all symbols from shared libraries up
>     front. And on
>         > x86_64 your main executable is really just another shared
>     library.
>
>         Yes, but does gdb reload everything on each execution? Every
>     time I
>         execute "run" I see the same slow behavior.  Loading the
>     symbols for
>         small tools like llvm-rc takes hardly any time at all (i.e. "file
>         llvm-rc" is almost instantaneous).  But executing it causes
>     gdb to chew
>         up CPU cycles for a while.  Every time.
>
>                                  -David
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