Messages in this thread | | | From | Lasse Collin <> | Subject | Re: [PATCH RFC 1/3] Decompressors: Add XZ decompressor module | Date | Thu, 25 Nov 2010 16:34:03 +0200 |
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On 2010-11-25 Andrew Morton wrote: > On Wed, 24 Nov 2010 22:51:52 +0200 > Lasse Collin <lasse.collin@tukaani.org> wrote: > > This patch: Add the main decompression code (xz_dec), testing > > module (xz_dec_test), wrapper script (xz_wrap.sh) for the xz > > command line tool, and documentation. The xz_dec module is > > enough to have a usable XZ decompressor e.g. for Squashfs. > > I'm not seeing any documentation which tells me how to create, > install and execute xs-compressed kernels. There are new makefile > targets?
The last paragraph under "XZ related components in the kernel" in Documentation/xz.txt mentions xzkern and xzmisc commands available for makefiles. They are defined in scripts/Makefile.lib and have some comments as documentation there too.
The Kconfig options to enable XZ-compressed kernel are added in the second patch. There is already an option to select the kernel compression method so I only added XZ to that list. I assume that people will find this option just like they have been able to find the other compression methods.
> > +#define bcj_x86_test_msbyte(b) ((b) == 0x00 || (b) == 0xFF) > > This should be written in C. It looks nicer, and so > bcj_x86_test_msbyte(*p++) won't explode.
Thanks. It's fixed in XZ Embedded git repository now:
git clone http://git.tukaani.org/xz-embedded.git (clone only, no WWW for now)
I will post updated patches when needed.
> > +static noinline_for_stack size_t bcj_x86( > > hm, but it uses little stack space.
I wrote that code 19 months ago and now it looks odd to me too. I remember that my idea was to minimize stack usage in this call stack:
xz_dec_run() -> xz_dec_bcj_run() -> xz_dec_lzma2_run() -> ...
I wanted to prevent the BCJ filters from being inlined into xz_dec_bcj_run() because inlining would have increased the maximum stack usage by 100-150 bytes.
The BCJ filters are called via bcj_apply() which is called in two places from xz_dec_bcj_run(). Since there are two calls to bcj_apply(), GCC won't inline it. It will only inline the BCJ filters into bcj_apply() and that's OK. So noinline_for_stack does nothing good here. Maybe my early version had only one call to bcj_apply() or something like that.
Anyway, I removed noinline_for_stacks. I tested it also when only one BCJ filter is enabled and with a few different GCC versions.
> > +static noinline_for_stack size_t bcj_x86( > > + struct xz_dec_bcj *s, uint8_t *buf, size_t size) > > The preferred style is > > static noinline_for_stack size_t bcj_x86(struct xz_dec_bcj *s, uint8_t *buf, > size_t size) > > or > > static noinline_for_stack size_t > bcj_x86(struct xz_dec_bcj *s, uint8_t *buf, size_t size) > > (lots of dittoes)
Fixed.
-- Lasse Collin | IRC: Larhzu @ IRCnet & Freenode
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