Re: [Qemu-devel] [PATCH v2, Ping] SMBIOS: Upgrade Type17 to v2.3, add Type2

[Laszlo Ersek]

On 02/18/14 20:17, Gabriel L. Somlo wrote:
> On Tue, Feb 18, 2014 at 11:21:33AM +0100, Gerd Hoffmann wrote:

> Using Fedora 20 live, I collected the SMBIOS table from the guest
> using "dmidecode --dump-bin", with the unpatched SeaBIOS
> (dmidecode_pc.bin), SeaBIOS with my patch applied (dmidecode_mac.bin),
> and again with unpatched SeaBIOS but with "-smbios file=dmidecode_mac.bin"
> on the QEMU command line (dmidecode_cmdline.bin).

[...]

> However, when I compare unmodified SMBIOS against what I get when
> supplying the patched binary table via command line, I get this:
> 
>   $ diff dmi_pc.txt dmi_cmdline.txt 
>   2c2
>   < Reading SMBIOS/DMI data from file dmidecode_pc.bin.
>   ---
>   > Reading SMBIOS/DMI data from file dmidecode_cmdline.bin.
>   4c4
>   < 10 structures occupying 298 bytes.
>   ---
>   > 11 structures occupying 657 bytes.
>   108,109c108,120
>   < Handle 0x7F00, DMI type 127, 4 bytes
>   < End Of Table
>   ---
>   > Handle 0x5F4D, DMI type 95, 83 bytes
>   > Unknown Type
>   >       Header and Data:
>   >               5F 53 4D 5F 32 1F 02 04 4B 00 00 00 00 00 00 00
>   >               5F 44 4D 49 5F D2 46 01 20 00 00 00 0B 00 24 00
>   >               00 18 00 00 01 02 00 E8 03 00 08 00 00 00 00 00
>   >               00 00 00 04 01 00 FF FF 42 6F 63 68 73 00 42 6F
>   >               63 68 73 00 30 31 2F 30 31 2F 32 30 31 31 00 00
>   >               01 1B 00
>   >       Strings:
>   >               ....
>   > 
>   > Invalid entry length (0). DMI table is broken! Stop.
> 
> No Type 2, no extra fields for Type 17, and a corrupt table to boot.

I had tested this qemu interface with my OVMF SMBIOS patches. It works.
(I used a Type 3 table.)

The problem in this case is that you can't just pass in a raw dump from
dmidecode. You need to prefix it with "smbios_header":

struct smbios_table {
    struct smbios_header header;
    uint8_t data[];
} QEMU_PACKED;

struct smbios_header {
    uint16_t length;
    uint8_t type;
} QEMU_PACKED;

You need to set "type" to 1 (SMBIOS_TABLE_ENTRY), and set "length" so
that it covers the entire "smbios_table" struct (ie. both header and
payload, where payload is your SMBIOS table). "length" is little endian.

Laszlo