On Sat, Aug 5, 2017 at 12:26 PM, Heinrich Schuchardt xypron.glpk@gmx.de wrote:
On 08/05/2017 06:19 PM, Rob Clark wrote:
On Sat, Aug 5, 2017 at 12:16 PM, Rob Clark robdclark@gmail.com wrote:
On Sat, Aug 5, 2017 at 12:12 PM, Heinrich Schuchardt xypron.glpk@gmx.de wrote:
On 08/05/2017 05:58 PM, Rob Clark wrote:
Some arch's have trouble with unaligned accesses. Technically EFI device-path structs should be byte aligned, and the next node in the path starts immediately after the previous. Meaning that a pointer to an 'struct efi_device_path' is not necessarily word aligned. See section 10.3.1 in v2.7 of UEFI spec.
This causes problems not just for u-boot, but also most/all EFI payloads loaded by u-boot on these archs. Fortunately the common practice for traversing a device path is to rely on the length field in the header, rather than the specified length of the particular device path type+subtype. So the EFI_DP_PAD() macro will add the specified number of bytes to the tail of device path structs to pad them to word alignment.
Technically this is non-compliant, BROKEN_UNALIGNED should *only* be defined on archs that cannot do unaligned accesses.
Signed-off-by: Rob Clark robdclark@gmail.com
I'm not sure if there are other arch's that need -DBROKEN_UNALIGNED
Mark, this is untested but I think it should solve your crash on the Banana Pi. Could you give it a try when you get a chance?
arch/arm/config.mk | 2 +- include/efi_api.h | 30 ++++++++++++++++++++++++++++++ lib/efi_loader/efi_device_path.c | 3 +++ 3 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/arch/arm/config.mk b/arch/arm/config.mk index 1a77779db4..067dc93a9d 100644 --- a/arch/arm/config.mk +++ b/arch/arm/config.mk @@ -28,7 +28,7 @@ LLVMS_RELFLAGS := $(call cc-option,-mllvm,) \ $(call cc-option,-arm-use-movt=0,) PLATFORM_RELFLAGS += $(LLVM_RELFLAGS)
-PLATFORM_CPPFLAGS += -D__ARM__ +PLATFORM_CPPFLAGS += -D__ARM__ -DBROKEN_UNALIGNED
NAK
We have more then ARM. And other architectures also create exceptions for unaligned access.
I hate platform specific code. It should not be used outside /arch.
To play it save you should not use _packed at all! Use memcpy to transfer between aligned and unaligned memory.
except for reasons I explained in the thread on the patch that added the __packed in the first place. Sorry, this is ugly but we have to do it.
well, to be fair, we don't *have* to do it. The alternative is disable EFI_LOADER on archs that cannot do unaligned accesses. But this seemed like the better option.
In which UEFI protocol do you need the packed structures? Why can't you use memcpy to provide/read the data in these protocols? Why can't you use padding on all architectures?
The device-path protocol, as described in section 10.3 in the UEFI spec. And as I already explained, the problem isn't just u-boot but also all the various efi payloads loaded and executed directly or indirectly by u-boot. Please feel free to send patches to these various projects to fix those problems on armv7/etc. I guess it will take a while to get them all upstream, if they are accepted (really, *why* are we using efi on these archs?) and trickle out into distros.
I'll repeat the section I previously quoted from 10.3.1 in the other email thread:
A Device Path is a series of generic Device Path nodes. The first Device Path node starts at byte offset zero of the Device Path. The next Device Path node starts at the end of the previous Device Path node. Therefore all nodes are byte-packed data structures that may appear on any byte boundary. All code references to device path notes must assume all fields are unaligned. Since every Device Path node contains a length field in a known place, it is possible to traverse Device Path nodes that are of an unknown type. There is no limit to the number, type, or sequence of nodes in a Device Path.
What we were doing before was incorrect. Sorry, but if we are implementing the UEFI spec, we need to implement the UEFI spec, not what we wish the UEFI spec was. I fixed the bug in u-boot, and that exposed the problem in openbsd's bootaa64.efi. But I've spent enough time looking at shim/fallback/grub to say that they probably have the same problem on armv7 (and any other arch's that cannot do unaligned access).
This patch allows us to not break stuff that currently works by accident on these archs, but do things correctly on aarch64 and archs that *can* do unaligned access. This is better than doing things incorrectly on aarch64, and better than breaking archs that relied on this existing bug in u-boot's UEFI implementation.
BR, -R