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

[Nick Terrell <terrelln@fb.com>]

> On Aug 21, 2020, at 9:29 AM, Paul Cercueil <paul@crapouillou.net> 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@crapouillou.net>
> ---
> 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].

[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
>