Hi Marco, On 21.04.2021 20:23, Marco Elver wrote: > On Wed, Apr 21, 2021 at 06:27PM +0200, Marco Elver wrote: >> On Wed, Apr 21, 2021 at 05:11PM +0200, Marco Elver wrote: >>> +Cc linux-arm-kernel >>> >> [...] >>>> I've managed to reproduce this issue with a public Raspberry Pi OS Lite >>>> rootfs image, even without deploying kernel modules: >>>> >>>> https://downloads.raspberrypi.org/raspios_lite_armhf/images/raspios_lite_armhf-2021-03-25/2021-03-04-raspios-buster-armhf-lite.zip >>>> >>>> # qemu-system-arm -M virt -smp 2 -m 512 -kernel zImage -append "earlycon >>>> console=ttyAMA0 root=/dev/vda2 rw rootwait" -serial stdio -display none >>>> -monitor null -device virtio-blk-device,drive=virtio-blk -drive >>>> file=/tmp/2021-03-04-raspios-buster-armhf-lite.img,id=virtio-blk,if=none,format=raw >>>> -netdev user,id=user -device virtio-net-device,netdev=user >>>> >>>> The above one doesn't boot if zImage z compiled from commit fb6cc127e0b6 >>>> and boots if compiled from 2e498d0a74e5. In both cases I've used default >>>> arm/multi_v7_defconfig and >>>> gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabi toolchain. >>> Yup, I've narrowed it down to the addition of "__u64 _perf" to >>> siginfo_t. My guess is the __u64 causes a different alignment for a >>> bunch of adjacent fields. It seems that x86 and m68k are the only ones >>> that have compile-time tests for the offsets. Arm should probably add >>> those -- I have added a bucket of static_assert() in >>> arch/arm/kernel/signal.c and see that something's off. >>> >>> I'll hopefully have a fix in a day or so. >> Arm and compiler folks: are there some special alignment requirement for >> __u64 on arm 32-bit? (And if there is for arm64, please shout as well.) >> >> With the static-asserts below, the only thing that I can do to fix it is >> to completely remove the __u64. Padding it before or after with __u32 >> just does not work. It seems that the use of __u64 shifts everything >> in __sifields by 4 bytes. >> >> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h >> index d0bb9125c853..b02a4ac55938 100644 >> --- a/include/uapi/asm-generic/siginfo.h >> +++ b/include/uapi/asm-generic/siginfo.h >> @@ -92,7 +92,10 @@ union __sifields { >> __u32 _pkey; >> } _addr_pkey; >> /* used when si_code=TRAP_PERF */ >> - __u64 _perf; >> + struct { >> + __u32 _perf1; >> + __u32 _perf2; >> + } _perf; >> }; >> } _sigfault; >> >> ^^ works, but I'd hate to have to split this into 2 __u32 because it >> makes the whole design worse. >> >> What alignment trick do we have to do here to fix it for __u64? > So I think we just have to settle on 'unsigned long' here. On many > architectures, like 32-bit Arm, the alignment of a structure is that of > its largest member. This means that there is no portable way to add > 64-bit integers to siginfo_t on 32-bit architectures. > > In the case of the si_perf field, word size is sufficient since the data > it contains is user-defined. On 32-bit architectures, any excess bits of > perf_event_attr::sig_data will therefore be truncated when copying into > si_perf. > > Feel free to test the below if you have time, but the below lets me boot > 32-bit arm which previously timed out. It also passes all the > static_asserts() I added (will send those as separate patches). > > Once I'm convinced this passes all others tests too, I'll send a patch. This fixes the issue I've observed on my test systems. Feel free to add: Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Thanks, > -- Marco > > > diff --git a/include/linux/compat.h b/include/linux/compat.h > index c8821d966812..f0d2dd35d408 100644 > --- a/include/linux/compat.h > +++ b/include/linux/compat.h > @@ -237,7 +237,7 @@ typedef struct compat_siginfo { > u32 _pkey; > } _addr_pkey; > /* used when si_code=TRAP_PERF */ > - compat_u64 _perf; > + compat_ulong_t _perf; > }; > } _sigfault; > > diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h > index d0bb9125c853..03d6f6d2c1fe 100644 > --- a/include/uapi/asm-generic/siginfo.h > +++ b/include/uapi/asm-generic/siginfo.h > @@ -92,7 +92,7 @@ union __sifields { > __u32 _pkey; > } _addr_pkey; > /* used when si_code=TRAP_PERF */ > - __u64 _perf; > + unsigned long _perf; > }; > } _sigfault; > > Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
