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Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h

From
Jeff King <peff@peff.net>
Date
Jan 23, 2014, 19:44 UTC
Message-ID
<20140123194401.GA31412@sigill.intra.peff.net>
In-Reply-To
<20140123194118.GT18964@google.com>
On Thu, Jan 23, 2014 at 11:41:18AM -0800, Jonathan Nieder wrote:
Show 13 quoted lines
> Jeff King wrote:
> 
> > Commit d60c49c (read-cache.c: allow unaligned mapping of the
> > index file, 2012-04-03) introduced helpers to access
> > unaligned data. Let's factor them out to make them more
> > widely available.
> >
> > While we're at it, we'll give the helpers more readable
> > names, add a helper for the "ntohll" form, and add the
> > appropriate Makefile knob.
> 
> Weird.  Why wasn't git broken on the relevant platforms before (given
> that no one has been setting NEEDS_ALIGNED_ACCESS for them)?

Because most of our data structures support aligned access. Thomas mentioned this as a potential issue earlier, and I said in a re-roll cover letter:

  I did not include the NEEDS_ALIGNED_ACCESS patch. I note that we do
  not even have a Makefile knob for this, and the code in read-cache.c
  has probably never actually been used. Are there real systems that
  have a problem? The read-cache code was in support of the index v4
  experiment, which did away with the 8-byte padding. So it could be
  that we simply don't see it, because everything is currently aligned.
I think it was a bug waiting to surface if index v4 ever got wide use.
-Peff
Previous: Jonathan NiederNext: Jonathan Nieder
Message 15 of 68 in “pack bitmaps”
  1. 0/22 pack bitmapsJeff King, Dec 21, 2013
  2. 01/23 sha1write: make buffer const-correctJeff King, Dec 21, 2013
  3. Christian CouderDec 22, 2013
  4. 02/23 revindex: Export new APIsJeff King, Dec 21, 2013
  5. 03/23 pack-objects: Refactor the packing listJeff King, Dec 21, 2013
  6. 04/23 pack-objects: factor out name_hashJeff King, Dec 21, 2013
  7. 05/23 revision: allow setting custom limiter functionJeff King, Dec 21, 2013
  8. 06/23 sha1_file: export `git_open_noatime`Jeff King, Dec 21, 2013
  9. 07/23 compat: add endianness helpersJeff King, Dec 21, 2013
  10. 08/23 ewah: compressed bitmap implementationJeff King, Dec 21, 2013
  11. Jonathan NiederJan 23, 2014
  12. Jeff KingJan 23, 2014
  13. 1/2 compat: move unaligned helpers to bswap.hJeff King, Jan 23, 2014
  14. Jonathan NiederJan 23, 2014
  15. Jeff KingJan 23, 2014
  16. Jonathan NiederJan 23, 2014
  17. Jeff KingJan 23, 2014
  18. Jonathan NiederJan 23, 2014
  19. Jeff KingJan 23, 2014
  20. 2/2 ewah: support platforms that require aligned readsJeff King, Jan 23, 2014
  21. Jonathan NiederJan 23, 2014
  22. Jeff KingJan 23, 2014
  23. Jonathan NiederJan 23, 2014
  24. Jeff KingJan 23, 2014
  25. Jonathan NiederJan 23, 2014
  26. Jeff KingJan 23, 2014
  27. Jeff KingJan 23, 2014
  28. Shawn PearceJan 23, 2014
  29. Jeff KingJan 23, 2014
  30. brian m. carlsonJan 23, 2014
  31. Jeff KingJan 23, 2014
  32. Jonathan NiederJan 23, 2014
  33. Jeff KingJan 23, 2014
  34. Jonathan NiederJan 23, 2014
  35. Jonathan NiederJan 23, 2014
  36. 0/3 unaligned reads from .bitmap filesJeff King, Jan 23, 2014
  37. 1/3 block-sha1: factor out get_be and put_be wrappersJeff King, Jan 23, 2014
  38. Jonathan NiederJan 23, 2014
  39. 2/3 read-cache: use get_be32 instead of hand-rolled ntoh_lJeff King, Jan 23, 2014
  40. Jonathan NiederJan 23, 2014
  41. Jeff KingJan 24, 2014
  42. 3/3 ewah: support platforms that require aligned readsJeff King, Jan 23, 2014
  43. Jonathan NiederJan 23, 2014
  44. Vicent MartíJan 23, 2014
  45. Jonathan NiederJan 24, 2014
  46. Jonathan NiederJan 23, 2014
  47. 09/23 documentation: add documentation for the bitmap formatJeff King, Dec 21, 2013
  48. 10/23 pack-bitmap: add support for bitmap indexesJeff King, Dec 21, 2013
  49. 11/23 pack-objects: split add_object_entryJeff King, Dec 21, 2013
  50. 12/23 pack-objects: use bitmaps when packing objectsJeff King, Dec 21, 2013
  51. 13/23 rev-list: add bitmap mode to speed up object listsJeff King, Dec 21, 2013
  52. 14/23 pack-objects: implement bitmap writingJeff King, Dec 21, 2013
  53. 15/23 repack: stop using magic number for ARRAY_SIZE(exts)Jeff King, Dec 21, 2013
  54. 16/23 repack: turn exts array into array-of-structJeff King, Dec 21, 2013
  55. 17/23 repack: handle optional files created by pack-objectsJeff King, Dec 21, 2013
  56. 18/23 repack: consider bitmaps when performing repacksJeff King, Dec 21, 2013
  57. 19/23 count-objects: recognize .bitmap in garbage-checkingJeff King, Dec 21, 2013
  58. 20/23 t: add basic bitmap functionality testsJeff King, Dec 21, 2013
  59. 21/23 t/perf: add tests for pack bitmapsJeff King, Dec 21, 2013
  60. 22/23 pack-bitmap: implement optional name_hash cacheJeff King, Dec 21, 2013
  61. 23/23 compat/mingw.h: Fix the MinGW and msvc buildsJeff King, Dec 21, 2013
  62. Erik Faye-LundDec 25, 2013
  63. Jeff KingDec 28, 2013
  64. Vicent MartíDec 28, 2013
  65. Ramsay JonesDec 28, 2013
  66. Jeff KingDec 21, 2013
  67. Jeff KingDec 21, 2013
  68. Thomas RastDec 21, 2013

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