Re: [PATCH 2/2] tools/libs/guest: Use the system liblz4 in the bzimage loader

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Jun 03, 2026 at 09:53:31AM +0100, Andrew Cooper wrote:
> Right now lz4, unlike every other compression scheme, unconditionally uses
> Xen's unsafe decompressor.  Make it consistent with all other compression
> schemes by using liblz4.
> 
> The unsafe decompression is still required for the MiniOS build, so rename
> xg_dom_decompress_lz4.c to xg_dom_decompress_unsafe_lz4.c and drop the
> non-MiniOS content.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

> ---
> CC: Anthony PERARD <anthony.perard@vates.tech>
> CC: Juergen Gross <jgross@suse.com>
> CC: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> ---
>  tools/libs/guest/Makefile.common              |   2 +-
>  tools/libs/guest/xg_dom_bzimageloader.c       | 128 +++++++++++++++-
>  tools/libs/guest/xg_dom_decompress.h          |   6 -
>  tools/libs/guest/xg_dom_decompress_lz4.c      | 143 ------------------
>  tools/libs/guest/xg_dom_decompress_unsafe.h   |   2 +
>  .../libs/guest/xg_dom_decompress_unsafe_lz4.c |  39 +++++
>  6 files changed, 169 insertions(+), 151 deletions(-)
>  delete mode 100644 tools/libs/guest/xg_dom_decompress.h
>  delete mode 100644 tools/libs/guest/xg_dom_decompress_lz4.c
>  create mode 100644 tools/libs/guest/xg_dom_decompress_unsafe_lz4.c
> 
> diff --git a/tools/libs/guest/Makefile.common b/tools/libs/guest/Makefile.common
> index b928a4a246a9..86b1f160e536 100644
> --- a/tools/libs/guest/Makefile.common
> +++ b/tools/libs/guest/Makefile.common
> @@ -46,7 +46,6 @@ OBJS-y                 += xg_dom_core.o
>  OBJS-y                 += xg_dom_boot.o
>  OBJS-y                 += xg_dom_elfloader.o
>  OBJS-$(CONFIG_X86)     += xg_dom_bzimageloader.o
> -OBJS-$(CONFIG_X86)     += xg_dom_decompress_lz4.o
>  OBJS-$(CONFIG_X86)     += xg_dom_hvmloader.o
>  OBJS-$(CONFIG_ARM)     += xg_dom_armzimageloader.o
>  OBJS-y                 += xg_dom_binloader.o
> @@ -59,6 +58,7 @@ OBJS-$(CONFIG_ARM)     += xg_dom_arm.o
>  ifeq ($(CONFIG_LIBXC_MINIOS),y)
>  OBJS-y                 += xg_dom_decompress_unsafe.o
>  OBJS-y                 += xg_dom_decompress_unsafe_bzip2.o
> +OBJS-y                 += xg_dom_decompress_unsafe_lz4.o
>  OBJS-y                 += xg_dom_decompress_unsafe_lzma.o
>  OBJS-y                 += xg_dom_decompress_unsafe_lzo1x.o
>  OBJS-y                 += xg_dom_decompress_unsafe_xz.o
> diff --git a/tools/libs/guest/xg_dom_bzimageloader.c b/tools/libs/guest/xg_dom_bzimageloader.c
> index 1fb4e5a1f728..32b3c682a447 100644
> --- a/tools/libs/guest/xg_dom_bzimageloader.c
> +++ b/tools/libs/guest/xg_dom_bzimageloader.c
> @@ -32,7 +32,6 @@
>  #include <inttypes.h>
>  
>  #include "xg_private.h"
> -#include "xg_dom_decompress.h"
>  
>  #include <xen-tools/common-macros.h>
>  
> @@ -623,6 +622,133 @@ static int xc_try_zstd_decode(
>  
>  #endif
>  
> +#if defined(HAVE_LZ4)
> +
> +#include <lz4.h>
> +
> +#define ARCHIVE_MAGICNUMBER 0x184C2102
> +
> +static int xc_try_lz4_decode(struct xc_dom_image *dom, void **blob, size_t *size)
> +{
> +    size_t outsize, insize;
> +    unsigned char *outbuf = NULL, *inp = *blob, *outp;
> +    uint32_t chunksize;
> +
> +    /* Magic, descriptor byte, and trailing size field. */
> +    if ( *size <= 8 )
> +    {
> +        DOMPRINTF("LZ4: insufficient input data");
> +        goto err;
> +    }
> +
> +    insize = *size - 4;
> +    outsize = get_unaligned_le32(*blob + insize);
> +
> +    if ( xc_dom_kernel_check_size(dom, outsize) )
> +    {
> +        DOMPRINTF("LZ4: output too large");
> +        goto err;
> +    }
> +
> +    outbuf = malloc(outsize);

I would use calloc() or memset() the buffer, just in case part of it
is (wrongly) left uninitialized, as this is copied into guest memory.

I see this is code moment, so possibly better to adjust afterwards if
anything.

Thanks, Roger.