[SeaBIOS] [PATCH v5 2/4] malloc: support looking up a given pattern in FSEG

[Kevin O'Connor]

On Wed, Sep 25, 2013 at 12:54:42PM +0300, Michael S. Tsirkin wrote:
> Will be used to find RSDP there.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  src/malloc.h |  1 +
>  src/malloc.c | 19 ++++++++++++++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/src/malloc.h b/src/malloc.h
> index af8a21d..feb8938 100644
> --- a/src/malloc.h
> +++ b/src/malloc.h
> @@ -19,6 +19,7 @@ void *_malloc(struct zone_s *zone, u32 handle, u32 size, u32 align);
>  int _free(void *data);
>  u32 malloc_getspace(struct zone_s *zone);
>  void *malloc_find(u32 handle);
> +void *malloc_find_fseg_pattern(void *pattern, unsigned pattern_size);
>  
>  #define MALLOC_DEFAULT_HANDLE 0xFFFFFFFF
>  // Minimum alignment of malloc'd memory
> diff --git a/src/malloc.c b/src/malloc.c
> index 281f41e..0f5fae7 100644
> --- a/src/malloc.c
> +++ b/src/malloc.c
> @@ -12,7 +12,7 @@
>  #include "output.h" // dprintf
>  #include "stacks.h" // wait_preempt
>  #include "std/optionrom.h" // OPTION_ROM_ALIGN
> -#include "string.h" // memset
> +#include "string.h" // memset, memcmp
>  
>  // Information on a reserved area.
>  struct allocinfo_s {
> @@ -273,6 +273,23 @@ _free(void *data)
>      return 0;
>  }
>  
> +// Find the data block in zone matching a given pattern.
> +void *malloc_find_fseg_pattern(void *pattern, unsigned pattern_size)
> +{
> +    extern u8 zonefseg_start[], zonefseg_end[];
> +    unsigned space = zonefseg_end - zonefseg_start;
> +    int off;
> +
> +    if (space < pattern_size)
> +        return NULL;
> +
> +    for (off = 0; off < space - pattern_size; ++off) {
> +        if (!memcmp(zonefseg_start + off, pattern, pattern_size))
> +            return zonefseg_start + off;
> +    }
> +    return NULL;
> +}

This shouldn't be in malloc.c - it's not part of the core memory
allocation system.  Either scan the whole of 0xf0000-0x100000, use
extern zonefseg_end/start in another file, or scan the allocations
made in romfile-loader.

Also, this shouldn't scan every byte for the pattern.  It should scan
on 16 byte boundaries and do the acpi checksum check.  See the code in
fw/biostable.c:copy_acpi_rsdp as an example.  Nothing stops something
else from allocating ram which happens to have an rsdp signature in
it.  It's unlikely, but not worth the risk.

The rest of the series looks okay to me.

-Kevin