[vlc-devel] [PATCH 1/2] compat: Workaround sendmsg bug on some ArmV8 Android devices

Hugo Beauzée-Luyssen hugo at beauzee.fr
Mon Apr 1 09:07:55 CEST 2019

On Fri, Mar 29, 2019, at 9:11 PM, Rémi Denis-Courmont wrote:
> Le perjantaina 29. maaliskuuta 2019, 15.22.51 EET Hugo Beauzée-Luyssen a écrit 
> :
> > > And FWIW, I don't agree with the assessment that bugs in libc syscall
> > > wrappers cannot be coded around - especially if you target only one
> > > specific ISA.
> > 
> > I can't see anything obviously wrong in the syscall wrapper:
> > https://android.googlesource.com/platform/bionic.git/+/refs/heads/master/li
> > bc/arch-arm64/syscalls/sendmsg.S But I can't say I'm fluent with Assembly
> > *at all*
> > I can't see anything in the libc's logs that points me to a fix there, hence
> > the feeling that the issue is more on the kernel level.
> Implying that you can see something wrong with the kernel code? If there was a 

Implying that I can't see anything wrong in the libc code.

> sign-expansion bug in the Linux system call dispatch on AArch64, it would 
> would affect a lot more system calls than just sendmsg on an old Android. If 
> there was a sign-expansion bug in the sengmsg system call itself, it would 
> affect all 64-bits platforms, some of which have been in broad use for longer 
> than Android has even existed.
> This rather questions if the alleged bug is even specific to AArch64 & sendmsg.

That I agree with, but the sendmsg one I was able to reproduce systematically.

  Hugo Beauzée-Luyssen
  hugo at beauzee.fr

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