qemu_arm_defconfig with LTO fails due to unaligned access

[Heinrich Schuchardt]

Am 8. März 2023 17:18:32 MEZ schrieb Tom Rini <trini at 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.

Best regards 

Heinrich