Re: [PATCH 2/2] MIPS: Add support for ZSTD-compressed kernels

[Paul Cercueil]

Hi Nick,

Le lun. 24 août 2020 à 19:51, Nick Terrell <terrelln@xxxxxx> a écrit 
:
> >  On Aug 21, 2020, at 9:29 AM, Paul Cercueil <paul@xxxxxxxxxxxxxxx> 
> > wrote:
> >
> >  Add support for self-extracting kernels with a ZSTD compression.
> >
> >  Tested on a kernel for the GCW-Zero, it allows to reduce the size 
> > of the
> >  kernel file from 4.1 MiB with gzip to 3.5 MiB with ZSTD, and boots 
> > just
> >  as fast.
> >
> >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> >  ---
> >  arch/mips/Kconfig                      |  1 +
> >  arch/mips/boot/compressed/Makefile     |  1 +
> >  arch/mips/boot/compressed/decompress.c |  4 ++++
> >  arch/mips/boot/compressed/string.c     | 16 ++++++++++++++++
> >  4 files changed, 22 insertions(+)
> >
> >  diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> >  index c95fa3a2484c..b9d7c4249dc9 100644
> >  --- a/arch/mips/Kconfig
> >  +++ b/arch/mips/Kconfig
> >  @@ -1890,6 +1890,7 @@ config SYS_SUPPORTS_ZBOOT
> >  	select HAVE_KERNEL_LZMA
> >  	select HAVE_KERNEL_LZO
> >  	select HAVE_KERNEL_XZ
> >  +	select HAVE_KERNEL_ZSTD
> >
> >  config SYS_SUPPORTS_ZBOOT_UART16550
> >  	bool
> >  diff --git a/arch/mips/boot/compressed/Makefile 
> > b/arch/mips/boot/compressed/Makefile
> >  index 6e56caef69f0..86ddc6fc16f4 100644
> >  --- a/arch/mips/boot/compressed/Makefile
> >  +++ b/arch/mips/boot/compressed/Makefile
> >  @@ -70,6 +70,7 @@ tool_$(CONFIG_KERNEL_LZ4)     = lz4
> >  tool_$(CONFIG_KERNEL_LZMA)    = lzma
> >  tool_$(CONFIG_KERNEL_LZO)     = lzo
> >  tool_$(CONFIG_KERNEL_XZ)      = xzkern
> >  +tool_$(CONFIG_KERNEL_ZSTD)    = zstd
>
> You can use zstd22 here. It will give you slightly better compression
> without any additional memory usage. Also, you should add
> -D__DISABLE_EXPORTS to the KBUILD_CFLAGS like x86 does [1].

Indeed, it's 0.01% smaller :)

What is __DISABLE_EXPORTS for?

-Paul

> [1] 
> https://github.com/torvalds/linux/blob/master/arch/x86/boot/compressed/Makefile
>
> -Nick
>
> >  targets += vmlinux.bin.z
> >  $(obj)/vmlinux.bin.z: $(obj)/vmlinux.bin FORCE
> >  diff --git a/arch/mips/boot/compressed/decompress.c 
> > b/arch/mips/boot/compressed/decompress.c
> >  index 88f5d637b1c4..c61c641674e6 100644
> >  --- a/arch/mips/boot/compressed/decompress.c
> >  +++ b/arch/mips/boot/compressed/decompress.c
> >  @@ -72,6 +72,10 @@ void error(char *x)
> >  #include "../../../../lib/decompress_unxz.c"
> >  #endif
> >
> >  +#ifdef CONFIG_KERNEL_ZSTD
> >  +#include "../../../../lib/decompress_unzstd.c"
> >  +#endif
> >  +
> >  const unsigned long __stack_chk_guard = 0x000a0dff;
> >
> >  void __stack_chk_fail(void)
> >  diff --git a/arch/mips/boot/compressed/string.c 
> > b/arch/mips/boot/compressed/string.c
> >  index 43beecc3587c..ab95722ec0c9 100644
> >  --- a/arch/mips/boot/compressed/string.c
> >  +++ b/arch/mips/boot/compressed/string.c
> >  @@ -27,3 +27,19 @@ void *memset(void *s, int c, size_t n)
> >  		ss[i] = c;
> >  	return s;
> >  }
> >  +
> >  +void *memmove(void *dest, const void *src, size_t n)
> >  +{
> >  +	unsigned int i;
> >  +	const char *s = src;
> >  +	char *d = dest;
> >  +
> >  +	if ((uintptr_t)dest < (uintptr_t)src) {
> >  +		for (i = 0; i < n; i++)
> >  +			d[i] = s[i];
> >  +	} else {
> >  +		for (i = n; i > 0; i--)
> >  +			d[i - 1] = s[i - 1];
> >  +	}
> >  +	return dest;
> >  +}
> >  --
> >  2.28.0