On Wed, Jul 23, 2025 at 12:01:28PM +0300, Daniil Tatianin wrote:
> This is useful to be able to indicate various supported features to the
> guest, or freeze a specific version of SeaBIOS to prevent guest visible
> changes between BIOS updates. This is currently not possible since the
> extension bytes indicated by SeaBIOS are slightly different than those
> QEMU sets by default.
>
> Signed-off-by: Daniil Tatianin <d-tatia...@yandex-team.ru>
> ---
> hw/smbios/smbios.c | 66 +++++++++++++++++++++++++++++++++---
> include/hw/firmware/smbios.h | 3 ++
> 2 files changed, 64 insertions(+), 5 deletions(-)
>
> diff --git a/hw/smbios/smbios.c b/hw/smbios/smbios.c
> index ad4cd6721e..73699e8a62 100644
> --- a/hw/smbios/smbios.c
> +++ b/hw/smbios/smbios.c
> @@ -178,6 +178,14 @@ static const QemuOptDesc qemu_smbios_type0_opts[] = {
> .name = "uefi",
> .type = QEMU_OPT_BOOL,
> .help = "uefi support",
> + },{
> + .name = "extension_byte_1",
> + .type = QEMU_OPT_NUMBER,
> + .help = "BIOS characteristics extension byte 1"
> + },{
> + .name = "extension_byte_2",
> + .type = QEMU_OPT_NUMBER,
> + .help = "BIOS characteristics extension byte 2"
> },
> { /* end of list */ }
> };
> @@ -572,10 +580,23 @@ static void smbios_build_type_0_table(void)
> t->bios_rom_size = 0; /* hardcoded in SeaBIOS with FIXME comment */
>
> t->bios_characteristics = cpu_to_le64(0x08); /* Not supported */
> - t->bios_characteristics_extension_bytes[0] = 0;
> - t->bios_characteristics_extension_bytes[1] = 0x14; /* TCD/SVVP | VM */
> - if (smbios_type0.uefi) {
> - t->bios_characteristics_extension_bytes[1] |= 0x08; /* |= UEFI */
> +
> + if (smbios_type0.have_extension_bytes[0]) {
> + t->bios_characteristics_extension_bytes[0] =
> + smbios_type0.extension_bytes[0];
> + } else {
> + t->bios_characteristics_extension_bytes[0] = 0;
> + }
> +
> + if (smbios_type0.have_extension_bytes[1]) {
> + t->bios_characteristics_extension_bytes[1] =
> + smbios_type0.extension_bytes[1];
> + } else {
> + t->bios_characteristics_extension_bytes[1] = 0x14; /* TCD/SVVP | VM
> */
> +
> + if (smbios_type0.uefi) {
> + t->bios_characteristics_extension_bytes[1] |= 0x08; /* |= UEFI */
> + }
should we not or these in, anyway?
> }
>
> if (smbios_type0.have_major_minor) {
> @@ -1403,7 +1424,42 @@ void smbios_entry_add(QemuOpts *opts, Error **errp)
> save_opt(&smbios_type0.vendor, opts, "vendor");
> save_opt(&smbios_type0.version, opts, "version");
> save_opt(&smbios_type0.date, opts, "date");
> - smbios_type0.uefi = qemu_opt_get_bool(opts, "uefi", false);
> +
> + if (qemu_opt_get(opts, "extension_byte_1")) {
> + uint64_t ex_val;
> +
> + ex_val = qemu_opt_get_number(opts, "extension_byte_1", 0);
> + if (ex_val > 0xFF) {
> + error_setg(errp, "Invalid extension_byte_1");
> + return;
> + }
> +
> + smbios_type0.extension_bytes[0] = ex_val;
> + smbios_type0.have_extension_bytes[0] = true;
> + }
> +
> + if (qemu_opt_get(opts, "extension_byte_2")) {
> + uint64_t ex_val;
> +
> + ex_val = qemu_opt_get_number(opts, "extension_byte_2", 0);
> + if (ex_val > 0xFF) {
> + error_setg(errp, "Invalid extension_byte_2");
> + return;
> + }
> +
> + smbios_type0.extension_bytes[1] = ex_val;
> + smbios_type0.have_extension_bytes[1] = true;
> + }
> +
> + if (qemu_opt_get(opts, "uefi")) {
> + if (smbios_type0.have_extension_bytes[1]) {
> + error_setg(errp, "'uefi' and 'extension_byte_2' are "
> + "mutually exclusive");
> + return;
> + }
> +
> + smbios_type0.uefi = qemu_opt_get_bool(opts, "uefi", false);
> + }
>
> val = qemu_opt_get(opts, "release");
> if (val) {
> diff --git a/include/hw/firmware/smbios.h b/include/hw/firmware/smbios.h
> index f066ab7262..67b3b28471 100644
> --- a/include/hw/firmware/smbios.h
> +++ b/include/hw/firmware/smbios.h
> @@ -24,6 +24,9 @@ typedef struct {
> const char *vendor, *version, *date;
> bool have_major_minor, uefi;
> uint8_t major, minor;
> +
> + bool have_extension_bytes[2];
> + uint8_t extension_bytes[2];
> } smbios_type0_t;
> extern smbios_type0_t smbios_type0;
>
> --
> 2.34.1
