Re: qemu_arm_defconfig with LTO fails due to unaligned access

[Tom Rini <trini@konsulko.com>]

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On Wed, Mar 08, 2023 at 08:19:32PM +0100, Heinrich Schuchardt wrote:
> 
> 
> Am 8. März 2023 17:18:32 MEZ schrieb Tom Rini <trini@konsulko.com>:
> >On Wed, Mar 08, 2023 at 05:12:26AM +0100, Heinrich Schuchardt wrote:
> >> Hello Ilias, hello Tom,
> >> 
> >> Tom tried to run qemu_arm_defconfig with CONFIG_LTO=y in gitlab. This
> >> failed as shown in protocol
> >> https://source.denx.de/u-boot/u-boot/-/jobs/589913/raw
> >> 
> >> Executing 'HII database protocols'
> >> test_hii_database_new_package_list:
> >> data abort
> >> pc : [<7ff39b98>]          lr : [<7ff87328>]
> >> reloc pc : [<00000b98>]    lr : [<0004e328>]
> >> sp : 7edf8cc0  ip : 0000000c     fp : 7ffe60ec
> >> r10: 00000000  r9 : 7eef8eb0     r8 : 7ffe0d02
> >> r7 : 00000000  r6 : 7ef0f8c8     r5 : 7ffe0cf0  r4 : 7ffe0cb4
> >> r3 : 7ffe0cef  r2 : 00000000     r1 : ffffffff  r0 : 00000000
> >> Flags: nzcv  IRQs off  FIQs off  Mode SVC_32
> >> Code: e2403002 e3a00000 e1500001 012fff1e (e1f320b2)
> >> UEFI image [0x00000000:0xffffffff] '/\selftest'
> >> Resetting CPU ..
> >> 
> >> Debugging shows:
> >> 
> >> efi_hii_sibt_string_ucs2_block_next() calls u16_strnlen() for an
> >> unaligned u16 string. Here "ldrh r2, [r3, #2]!" is executed for
> >> unaligned r3. This should be allowable for SCTLR.A = 0.
> >> 
> >> When the crash occurs SCRLR has value 0xc5187f. SCTLR.A is bit 1 with
> >> value 1.
> >> 
> >> The implementation of allow_unaligned() in
> >> arch/arm/cpu/armv7 /sctlr.S should have set the flag to 0.
> >> arch/arm/cpu/armv7/sctlr.S is compiled (as demonstrated by adding #error
> >> to the code).
> >> 
> >> If I remove the weak implementation of allow_unaligned() in
> >> lib/efi_loader/efi_setup.c, the error does not occur.
> >> 
> >> Shouldn't building with LTO ignore the weak implementation?
> >> 
> >> If I add a printf() statement to the weak implemenation, the printf()
> >> command is not executed but
> >> 
> >> SCTLR 0xc5187d, SCTLR.A=0
> >> 
> >> The test passes as unaligned access is allowable.
> >> 
> >> I was building inside the Docker image with the GCC downloaded by
> >> buildman (gcc-12.2.0-nolibc/arm-linux-gnueabi).
> >> 
> >> To me this looks like a compiler issue.
> >
> >Interesting, yes. It seems like it shouldn't be too hard to come up with
> >a condensed example where the assembly function isn't used but instead
> >the weak C function is.
> >
> >And as a work-around, re-doing the code so that path_to_uefi() just
> >checks for ARM && !ARM64 before calling allow_unaligned() and not doing
> >the weak function trick should also be fine.
> >
> 
> We have more places in our code using weak functions. There many cases not covered by CI.
> 
> Just looking at EFI may not be adequate.

Yes, there's a more general issue with weak functions where the non-weak
version is in assembly rather than C. I think we've addressed those
already, however, but it's good to note and should probably get
documented.

-- 
Tom

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