Re: Greatly increased GDB memory and CPU usage with newest embedded ARM toolchain

[David Blaikie <dblaikie@gmail.com>]

Oh, managed to get the lto case to stop & valgrind to log it.

Yeah... peaked out over 5GB of memory usage, and:

74.12% (4,372,282,848B) 0x3A4D42: macro_alloc

On Sun, Apr 18, 2021 at 9:57 PM David Blaikie <dblaikie@gmail.com> wrote:

> 4My high water mark reported my massif for the non-lto build was 197MB -
> most of that seems to come from decoding the macro information
> (dwarf_decode_macros). You could try dropping down from -g3 to -g2 to see
> if that helps. (I realize the linux kernel uses a bunch of macros and
> benefits from debug info for macros, but it'd at least help isolate the
> problem - might help clarify whether the lto case is related or. not)
>
> On Sun, Apr 18, 2021 at 10:02 AM R. Diez <rdiezmail-binutils@yahoo.de>
> wrote:
>
>>
>>  > [...]
>> > & yeah, that does seem like quite a bit of RAM usage for a relatively
>> > small amount of debug info. Though I'm not a regular/frequent gdb
>> > developer, so I don't have any particular insight there - if no one
>> > else chimes in, might be worth running valgrind --tool=massif to get a
>> > memory profile, might point to what part of gdb is using all the RAM.
>>
>> I am worried that I may not be building the toolchain and/or GDB
>> correctly.
>>
>> Could you do the following test for me, just to confirm that you are
>> indeed seeing such a high memory consumption?
>>
>> Could you build GDB 10.1 for ARM? This is how I am configuring it for
>> cross-debugging (somewhat simplified):
>>
>> configure \
>>    CFLAGS="-g0 -O3 -flto=9 -march=native" \
>>    CXXFLAGS="-g0 -O3 -flto=9 -march=native" \
>>    --target=arm-none-eabi
>>
>> Maybe you want to build it without -O3 and LTO, just using the defaults.
>> I have been using those flags for years with previous versions without any
>> issues.
>>
>> Then load one of the .elf files in the attachment like this. There is no
>> need to have any ARM CPU available:
>>
>> ./arm-none-eabi-gdb firmware-debug-non-lto.elf
>>
>> At this point, GDB should be using less than 15 MiB of RAM.
>>
>> Now issue this GDB command:
>>
>> print StartOfUserCode
>>
>> You should see an output like this:
>>
>> $1 = {void (void)} 0x866d8 <StartOfUserCode()>
>>
>> Did that take more than 1 second? How much RAM is your GDB using now?
>>
>> If you repeat that with firmware-release-lto.elf , how much memory is
>> your GDB using? Be prepared to kill it before it breaks your system though.
>> I
>> normally kill it after a few seconds when it reaches 2 GiB of RAM.
>>
>> Thanks in advance,
>>    rdiez
>>
>