Re: [PATCH v2 0/9] hw, ui, virtfs-proxy-helper: Reduce QEMU .data/.rodata/.bss footprint

[Daniel P . Berrangé]

On Thu, Mar 05, 2020 at 01:45:16PM +0100, Philippe Mathieu-Daudé wrote:
> Since v1:
> - merged 2 series
> - reworked hw/usb/quirks
> - added R-b/A-b tags
> 
> This series reduce the footprint of the QEMU binary:
> .bss: 106KiB (moved to .heap)

Did this actually have an impact on the binary size, or just on the
size the elf-dissector reports ?  I'm not very familiar with ELF,
but Wikipedia's description of BSS makes me question it...

  "Typically only the length of the bss section, but no data, 
   is stored in the object file. The program loader allocates 
   memory for the bss section when it loads the program. On
   some platforms, some or all of the bss section is initialized
   to zeroes. Unix-like systems and Windows initialize the bss 
   section to zero"

This suggests .bss has no on-disk overhead, only runtime overhead,
which is presumably going to be the same with heap allocations.

> .data: 1MiB
> .rodata: 4.34MiB

These looks useful though in terms of disk footprint.

> (sizes on x86_64 building with -Os)
> 
> The elf-dissector tool [1] [2] helped to notice the big array.
> 
> [1] https://phabricator.kde.org/source/elf-dissector/
> [2] https://www.volkerkrause.eu/2019/06/22/elf-dissector-aarch64-support.html
> [heap equivalent tool working with QEMU: https://github.com/KDE/heaptrack]
> 
> Supersedes: <address@hidden>
> Supersedes: <address@hidden>
> 
> Philippe Mathieu-Daudé (9):
>   hw/audio/fmopl: Fix a typo twice
>   hw/audio/fmopl: Move ENV_CURVE to .heap to save 32KiB of .bss
>   hw/audio/intel-hda: Use memory region alias to reduce .rodata by
>     4.34MB
>   hw/net/e1000: Add readops/writeops typedefs
>   hw/net/e1000: Move macreg[] arrays to .rodata to save 1MiB of .data
>   hw/usb/quirks: Use smaller types to reduce .rodata by 10KiB
>   ui/curses: Make control_characters[] array const
>   ui/curses: Move arrays to .heap to save 74KiB of .bss
>   virtfs-proxy-helper: Make the helper_opts[] array const
> 
>  hw/usb/quirks.h             | 22 +++++++++++++---------
>  fsdev/virtfs-proxy-helper.c |  2 +-
>  hw/audio/fmopl.c            |  8 +++++---
>  hw/audio/intel-hda.c        | 24 ++++++++++--------------
>  hw/net/e1000.c              |  6 ++++--
>  hw/net/e1000e_core.c        |  6 ++++--
>  hw/usb/quirks.c             |  4 ++--
>  ui/curses.c                 | 10 +++++++---
>  8 files changed, 46 insertions(+), 36 deletions(-)
> 
> -- 
> 2.21.1
> 
> 

Regards,
Daniel
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