[Buildroot] [PATCH] ubifs: Fix regression in ubifs_readdir()

["Jörg Krause" <joerg.krause@embedded.rocks>]

On Thu, 2016-11-03 at 03:46 +0100, Arnout Vandecappelle wrote:
> 
> On 02-11-16 23:49, J?rg Krause wrote:
> > On Wed, 2016-11-02 at 21:49 +0100, Thomas Petazzoni wrote:
> > > Hello,
> > > 
> > > On Wed, 02 Nov 2016 20:56:59 +0100, J?rg Krause wrote:
> > > 
> > > > > This is *really* bad. Which Buildroot version are you
> > > > > using???
> > > > 
> > > > 2016.11 #
> > > > 
> > > > Note that I am using Buildroot as a submodule [1] and I needed
> > > > to
> > > > port
> > > > the br2-external tree. Maybe I messed something up?
> > > > 
> > > > > Are you able to reproduce the bad ccache behavior here???
> > > > 
> > > > Yes, I am. Linux kernel source directory is located locally and
> > > > the
> > > > path is set using LINUX_OVERRIDE_SRCDIR in local.mk.
> > > > 
> > > > 1/ Checkout Linux kernel version 4.7.10
> > > > 2/ make linux-dirclean all
> > > > 3/ Booted Linux version is 4.7.10
> > > > 
> > > > 4/ Checkout Linux kernel version 4.8.5
> > > > 5/ make linux-dirclean all
> > > > 6/ Booted Linux version is still 4.7.10
> > > 
> > > And this scenario works fine with ccache *disabled*, but breaks
> > > when
> > > you enable ccache support in Buildroot?
> > 
> > Yes.
> 
> ?I can't reproduce this. I've got a nice mix of cache misses and
> cache hits when
> building a different version, and version.o is definitely a cache
> miss.
> 
> ?Can you double-check the version in output/build/linux-
> custom/init/version.o?

I checked the version string in version.o with hexdump -C and they
differ.

> And the one in output/build/linux-
> custom/include/generated/utsrelease.h?

This as well.

> ?Hm, hang on, is there maybe a utsrelease.h that ends up in your
> staging dir and that is used by ccache?

No, there is only the linux generated file.

---

I am not experienced with ccache, but I got some statistics:

I cleared the cache by removing ~/.buildroot-ccache, than run `make
linux-dirclean linux`:

cache hit (direct)?????????????????????0
cache hit (preprocessed)???????????????0
cache miss??????????????????????????1088
cache hit rate??????????????????????0.00 %
called for link???????????????????????10
called for preprocessing???????????????5
no input file????????????????????????394
cleanups performed?????????????????????0
files in cache??????????????????????3250

Then I re-run `make linux-dirclean linux` (without altering the linux
sources):

cache hit (direct)??????????????????1076
cache hit (preprocessed)??????????????10
cache miss??????????????????????????1090
cache hit rate?????????????????????49.91 %
called for link???????????????????????20
called for preprocessing??????????????10
no input file????????????????????????788
cleanups performed?????????????????????0
files in cache??????????????????????3264

Again, clear the cache and run `make linux-dirclean linux`, but alter
the linux sources by checking out a different branch:

cache hit (direct)????????????????????10
cache hit (preprocessed)??????????????62
cache miss??????????????????????????2102
cache hit rate??????????????????????3.31 %
called for link???????????????????????20
called for preprocessing??????????????10
no input file????????????????????????773
cleanups performed?????????????????????0
files in cache??????????????????????6386

---

Furthermore, I did the following for the different linux builds:

After building branch-4.7.y:
# cp output/build/linux-custom/arch/arm/boot/zImage zImage-4.7.10

After building branch-4.8.y:
# cp output/build/linux-custom/arch/arm/boot/zImage zImage-4.8.5

Afterwards, diff shows no differences:
# diff zImage-4.7.10 zImage-4.8.5

Best regards,
J?rg Krause