ACK: [SRU][N:azure][PATCH v2 0/1] Ubuntu 24.04 for Azure unable to run 32bit binaries (LP: #2071445)

[Manuel Diewald]

On Mon, Jul 15, 2024 at 05:01:19PM +0200, Juerg Haefliger wrote:
> BugLink: https://bugs.launchpad.net/bugs/2071445
> 
> [Impact]
> 
> ## Issue details
> 
> The configuration of the kernel in linux-image-6.8.0-1008-azure is incompatible with the way libc6:i386 is built.
> This leads to the error "The futex facility returned an unexpected error code." and application crash when trying to execute many 32bit applications in x86-64 machines.
> 
> In very short the issue is the following:
> This kernel image is compiled with CONFIG_COMPAT_32BIT_TIME=n, unlike the vanilla Ubuntu 24.04 kernel images.
> But, the glibc / libc6:i386 distributed with Ubuntu24.04 is compiled needing the syscalls enabled with that option.
> i.e. **This kernel configuration is just incompatible with the provided glibc**
> 
> In detail:
> glibc when built for 32bit, if not told which kernel is built for, will decide if the time_t value fits or not in a 32bit time_t, and do either the 32 or 64bit syscall:
> https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/futex-internal.c;h=0bb1dd51f66802521afd71b9246222ed0ea0d862;hb=refs/heads/release/2.39/master#l90
> calls with no deadline fit in the 32bit version, but as the kernel does not provide this syscall, glibc will just get  a ENOSYS, and glibc will error out aborting the program
> ```
> abort (abort.c:79)
> __libc_message_impl.cold (libc_fatal.c:132)
> __libc_fatal (libc_fatal.c:141)
> futex_fatal_error (futex-internal.h:87)
> __futex_abstimed_wait_common (futex-internal.c:119)
> ```
> after printing "The futex facility returned an unexpected error code.\n":
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/nptl/futex-internal.h;h=0e87e92d15ab92f5069463719a494e97d9800431;hb=refs/heads/release/2.39/master#l87
> 
> ## Expected behavior:
> 
> * No crashes for 32bit applications with this kernel
> * This kernel image built with CONFIG_COMPAT_32BIT_TIME=y
> 
> ## Aditional info:
> 
> For reference, this is the current vanilla Ubuntu 24.04 kernel for x86_64 and this config:
> ```
> $ uname -a
> Linux <redacted> 6.8.0-35-generic #35-Ubuntu SMP PREEMPT_DYNAMIC Mon May 20 15:51:52 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
> $ grep CONFIG_COMPAT_32BIT_TIME /boot/config-$(uname -r)
> CONFIG_COMPAT_32BIT_TIME=y
> ```
> 
> On the other hand this is the kernel config for this kernel image:
> ```
> Linux <> 6.8.0-1008-azure #8-Ubuntu SMP Fri May 17 10:44:55 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
> # CONFIG_COMPAT_32BIT_TIME is not set
> ```
> 
> Related github issue (the issue was found in github ubuntu 24.04 runners)
> https://github.com/actions/runner-images/issues/9977
> 
> [Fix]
> 
> Reenable COMPAT_32BIT_TIME
> 
> [Test Case]
> 
> See above.
> 
> [Where Problems Could Occur]
> 
> Disabling COMPAT_32BIT_TIME in Noble azure introduced a regression when running x86 binaries, so the fix is not expected to break anything (new).
> 
> Juerg Haefliger (1):
>   UBUNTU: [Config] azure: Revert "UBUNTU: [Config] azure: Disable
>     CONFIG_COMPAT_32BIT_TIME"
> 
>  debian.azure/config/annotations | 3 ---
>  1 file changed, 3 deletions(-)
> 
> -- 
> 2.40.1
> 
> 
> -- 
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

Acked-by: Manuel Diewald <manuel.diewald at canonical.com>

-- 
 Manuel
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