On 07/14/13 13:41, Michael S. Tsirkin wrote: > On Fri, Jul 12, 2013 at 04:17:28PM +0200, Laszlo Ersek wrote: >> On 07/10/13 15:51, Michael S. Tsirkin wrote:
>>> +struct BiosLinkerLoaderEntry { >>> + uint32_t command; >>> + union { >>> + /* >>> + * COMMAND_ALLOCATE - allocate a table from @alloc_file >>> + * subject to @alloc_align alignment (must be power of 2) >>> + * and @alloc_zone (can be HIGH or FSEG) requirements. >>> + * >>> + * Must appear exactly once for each file, and before >>> + * this file is referenced by any other command. >>> + */ >>> + struct { >>> + char alloc_file[BIOS_LINKER_LOADER_FILESZ]; >>> + uint32_t alloc_align; >>> + uint8_t alloc_zone; >>> + }; >> >> I think in OVMF we won't rely on the alloc_zone / alloc_align members, >> but that's OVMF's private business. > > RSDP must be in FSEG though I didn't express myself clearly, sorry. The default edk2 ACPI table protocol that OVMF uses should allocate RSDP and the like automatically in correct regions. (Allocating reserved memory for External(XXXX,OpRegionObj) needs a different call though.) >>> + >>> + /* padding */ >>> + char pad[124]; >>> + }; >> >> The unnamed union member is a gcc-ism. I'd give it a short name (like >> "u"), but feel free to ignore this. >> > > This isn't a gcc-ism. It's in C1x: > > An unnamed member whose type specifier is a structure specifier with no > tag is called an anonymous structure; an unnamed member whose type > specifier is a union specifier with no tag is called an anonymous union. > The members of an anonymous structure or union are considered to be > members of the containing structure or union. This applies recursively > if the containing structure or union is also anonymous. This part of the discussion is academic, but the unnamed union member is a gcc-ism in the qemu source, because AFAIK qemu uses the gnu89 dialect by default, and gnu99 on Solaris. >>> +}; >>> +typedef struct BiosLinkerLoaderEntry BiosLinkerLoaderEntry; >> >> Probably not needed in practice, but for documentation purposes I >> suggest QEMU_PACKED from "include/qemu/compiler.h". > > It's not required in practice but I can add this though I'm not sure - > what does this document? To me it documents that we rely on the absence of inter-member padding. Thanks Laszlo