Re: [Libunwind-devel] Minimum Linux Version requirements for libunwind?

[John Knight]

Thanks Luke for your response.  This is good information.

According to the man page for backtrace, it indicates that "backtrace(), 
backtrace_symbols(), and backtrace_symbols_fd() are provided in glibc since 
version 2.1".  Sorry for any confusion on this.
Unfortunately, my glibc is apparently older than 2.1.  I am not sure exactly 
how to tell how old... the usual method to try to run the libc.so.1 to get the 
version number results in a segmentation fault.  Ldd --version is not 
understood by ldd as well.  I also tried to use the gnu_get_libc_version() 
function that is supposed to always work, but it does not exist on my system.  
I think my glibc is very old... libc-so.1 vs libc-so.6 I am seeing commonly 
referenced.  Sigh.

So to summarize, my linux kernel is 3.14.77,  glibc is old (version ????), and 
gcc is 4.8.3.

Anyhow, I am being unsuccessful at getting libunwind working too.  It prints 
one stack backtrace step for __clone + 80 and then exits.  I know there is one 
function call from the signal handler to get to the backtrace() function, so 
this looks bogus.  I just need a backtrace capability that works.  This is an 
embedded linux environment and I am restricted as to software updates I can do, 
so I think I am between a rock and a hard place.

John


-----Original Message-----
From: Luke Diamand <address@hidden>
Sent: Tuesday, May 22, 2018 1:50 AM
To: John Knight <address@hidden>
Cc: address@hidden
Subject: Re: [Libunwind-devel] Minimum Linux Version requirements for libunwind?

On 22 May 2018 at 00:55, John Knight <address@hidden> wrote:
> Hi,
>
>
>
> I am trying to get libunwind to work on an ARM processor running an
> older version of linx (version 3.14.77).  I am wondering if there are
> any particular requirements of the Linux kernel or supporting
> libraries that would prohibit me from running on this older kernel?
> If so, what is the minimum kernel version required for libunwind?

I don't think it has any special kernel dependencies unless you're going to a 
really old kernel version (?). I'm using libunwind with 3.10.

>
> This kernel does NOT have support of backtrace()… my understanding is
> that support came with glibc in version 3.2 which had kernel support
> for it.  The lack of a backtrace has led me to try and use libunwind
> as an alternative to give me a stack backtrace when my program SEG faults.

I didn't think backtrace was a kernel feature - doesn't it live in glibc? And 
uses unwind tables generated by gcc/g++ together with the unwinding code in 
libstdc++ (as per the ABI).

If you're using glibc's backtrace() with unwind tables rather than frame 
pointer unwinding then you'll need a gcc that's new enough to generate it (and 
enable generation). That's been mostly there for a decade or more, but I think 
a bug was fixed recently (gcc 4.9.4/5.2
timeframe) for some obscure corner-cases.

But back to your question, I think the oldest kernel version I've used 
libunwind with is 3.0 with glibc=2.18 and gcc=4.9.

Luke

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