Il 21/01/2013 00:42, David Woodhouse ha scritto: > The main issue I have on the OVMF side is that it locks the entire > memory region from 0xC0000-0xFFFFF to be read-only, right before > invoking the Legacy16Boot method. This upsets SeaBIOS, which puts a > stack in the E0000 segment for use during hardware interrupts and other > calls which may otherwise overflow a caller's stack. There isn't > anywhere *else* it could put this stack, easily. > > We're contemplating a hack where its Legacy16PrepareToBoot method sets a > flag that tells the IRQ handler *not* to switch to its own stack, and > we'll just assume the stack provided by OVMF is big enough. And then the > Boot method will re-enable writes to the 0xE0000 segment before clearing > that flag again. > > The implementation of this would be horrid, and it's made even more > horrid by the fact that it would then have to do the platform-specific > unlocking in its Legacy16Boot method, before re-enabling the normal > stack-swapping code. And the CSM isn't really supposed to do that kind > of platform-specific stuff. > > Commenting out the ->LegacyRegion->Lock() call in GenericLegacyBoot() > obviously makes this problem go away for now, but that's obviously not > the right answer in the general case. > > If OVMF were to protect just the option roms and the region into which > it loaded the CSM image, leaving the RAM in between writeable, that > would conform to the existing spec, wouldn't it? If we can do *that*, > then potentially I could do something evil like compressing the CSM code > so that it fits into 64KiB, then having it decompress itself. So OVMF > only locks the region from 0xF0000-0xFFFFF into which it actually loaded > code, leaving the range age 0xE0000 onwards writeable as RAM.
You are in control of the EFI_LEGACY_REGION_PROTOCOL implementation though. If SeaBIOS needs 0xE0000-0xFFFFF to be always writable, just make a Lock of that region a no-op... Paolo ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. SALE $99.99 this month only -- learn more at: http://p.sf.net/sfu/learnmore_122412 _______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
