Re: libc6 Compatibility

>>>>> On Tue, 14 Jun 2022 21:55:58 +0200 (CEST), Sysadmin Lists said:
> 
> > ----------------------------------------
> > From: Dmitry Chagin <dchagin@freebsd.org>
> > Sent: Tue Jun 14 09:24:37 CEST 2022
> > To: Sysadmin Lists <sysadmin.lists@mailfence.com>
> > Cc: Freebsd Emulation <freebsd-emulation@freebsd.org>
> > Subject: Re: libc6 Compatibility
> > 
> > 
> > On Tue, Jun 14, 2022 at 03:26:03AM +0200, Sysadmin Lists wrote:
> > > Does Linux compat not work with Ubuntu's newest libc6 update?
> > > I used to run Brave browser from it, but now I get this error message:
> > > 
> > > $ /compat/ubuntu/opt/brave.com/brave/brave
> > > ELF interpreter /lib64/ld-linux-x86-64.so.2 not found, error 2
> > > Abort trap
> > > 
> > > The shared object is loaded in memory:
> > > $ ldd /opt/brave.com/brave/brave  | grep ld-
> > > 	/lib64/ld-linux-x86-64.so.2 (0x0000000001021000)
> > > 
> > > And it exists on the filesystem:
> > > $ find /compat/ubuntu/lib**/ -name ld-\* -exec ls -lh '{}' +
> > > -rwxr-xr-x  1 root  wheel   187K Dec 16  2020 /compat/ubuntu/lib/x86_64-linux-gnu/ld-2.31.so
> > > lrwxr-xr-x  1 root  wheel      10B Dec 16  2020 /compat/ubuntu/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 -> ld-2.31.so
> > > lrwxr-xr-x  1 root  root         34B Mar 23  2021 /compat/ubuntu/lib64/ld-linux-x86-64.so.2 -> ../lib/x86_64-linux-gnu/ld-2.31.so
> > > 
> > > This is the update that broke it:
> > > $ apt-get install libc6
> > > Get:1 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libc6 amd64 2.31-0ubuntu9.9 [2722 kB]
> > >
> > 
> > try ktrace it, aka ktrace -di /compat/ubuntu/opt/brave.com/brave/brave
> > then kdump -HAR -m 128 > brave.log
> > 
> > 
> 
> Thanks, Dmitry. That helped me find the problem. Here's the full log:
> 
> $ cat brave.log 
>   8184 101222 ktrace   0.000000 RET     F64  ktrace 0
>   8184 101222 ktrace   0.000014 CALL   F64  execve(0x7fffffffeda3,0x7fffffffeac0,0x7fffffffead0)
>   8184 101222 ktrace   0.000003 NAMI  F64  "/compat/ubuntu/opt/brave.com/brave/brave"
>   8184 101222 ktrace   0.055726 NAMI  F64  "/compat/ubuntu/lib64/ld-linux-x86-64.so.2"
>   8184 101222 ktrace   0.000032 NAMI  F64  "/lib64/ld-linux-x86-64.so.2"
> 
> And here's an updated `ls' printout after upgrading libc6:
> $ find /compat/ubuntu/lib**/ -name ld-\* -exec ls -lh '{}' +
> -rwxr-xr-x  1 root  wheel   187K Apr  6 18:24 /compat/ubuntu/lib/x86_64-linux-gnu/ld-2.31.so
> lrwxr-xr-x  1 root  wheel      10B Apr  6 18:24 /compat/ubuntu/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 -> ld-2.31.so
> lrwxr-xr-x  1 root  wheel      32B Apr  6 18:24 /compat/ubuntu/lib64/ld-linux-x86-64.so.2 -> /lib/x86_64-linux-gnu/ld-2.31.so
> 
> The new .so is missing 'previous directory' dots in the symlink path.

It looks like the link with the dots was made by hand in 2021, presumably to
fix this.

> I thought Linux compat was designed to search compat.linux.emul_path
> for shared libs first, but apparently it works differently than that.

What does linux compat do in general with absolute symlinks?  Does it check
the target with compat.linux.emul_path prepended?

__Martin