llvm dev - Nov 2014 - [LLVMdev] Proposal: add Go frontend subproject based on llgo

On Thu, Nov 20, 2014 at 12:19:06AM +0100, Joerg Sonnenberger
wrote:
> On Wed, Nov 19, 2014 at 01:53:17PM -0800, Peter Collingbourne wrote:
> > llgo depends on certain third-party components, namely a copy of the
Go
> > standard library (libgo), a Go program analysis library (go.tools) and
two
> > library dependencies of the standard library (libbacktrace and
libffi).
> 
> I think providing a better alternative to libffi is already a goal of
> some people, but what is libbacktrace needed for? What is not provided
> by the Itanium Unwind ABI?
According to the libbacktrace readme file:
> As of September 2012, libbacktrace only supports ELF executables with
> DWARF debugging information.  The library is written to make it
> straightforward to add support for other object file and debugging
> formats.
Ian (the author of libbacktrace) may be able to provide more context.

Thanks,
-- 
Peter

On Wed, Nov 19, 2014 at 4:58 PM, Peter Collingbourne <peter at pcc.me.uk>
wrote:
> On Thu, Nov 20, 2014 at 12:19:06AM +0100, Joerg Sonnenberger wrote:
>> On Wed, Nov 19, 2014 at 01:53:17PM -0800, Peter Collingbourne wrote:
>> > llgo depends on certain third-party components, namely a copy of
the Go
>> > standard library (libgo), a Go program analysis library (go.tools)
and two
>> > library dependencies of the standard library (libbacktrace and
libffi).
>>
>> I think providing a better alternative to libffi is already a goal of
>> some people, but what is libbacktrace needed for? What is not provided
>> by the Itanium Unwind ABI?
>
> According to the libbacktrace readme file:
>
>> As of September 2012, libbacktrace only supports ELF executables with
>> DWARF debugging information.  The library is written to make it
>> straightforward to add support for other object file and debugging
>> formats.
>
> Ian (the author of libbacktrace) may be able to provide more context.
I'm not sure I know the context for which I am providing context.
That said, libbacktrace is not an instantiation of the unwind ABI, it
is a client.  The unwind ABI gives you a call stack but only provides
PC and SP values.  libbacktrace gives you function names, file names,
and line numbers.  It does this by reading the debug info at runtime;
at present it only supports DWARF.

Ian

On Wed, Nov 19, 2014 at 04:58:08PM -0800, Peter Collingbourne
wrote:
> On Thu, Nov 20, 2014 at 12:19:06AM +0100, Joerg Sonnenberger wrote:
> > On Wed, Nov 19, 2014 at 01:53:17PM -0800, Peter Collingbourne wrote:
> > > llgo depends on certain third-party components, namely a copy of
the Go
> > > standard library (libgo), a Go program analysis library
(go.tools) and two
> > > library dependencies of the standard library (libbacktrace and
libffi).
> > 
> > I think providing a better alternative to libffi is already a goal of
> > some people, but what is libbacktrace needed for? What is not provided
> > by the Itanium Unwind ABI?
> 
> According to the libbacktrace readme file:
> 
> > As of September 2012, libbacktrace only supports ELF executables with
> > DWARF debugging information.  The library is written to make it
> > straightforward to add support for other object file and debugging
> > formats.
My question still stands. Do you use it for nice backtraces in debugging
situations?

Joerg

On Thu, Nov 20, 2014 at 03:16:49PM +0100, Joerg Sonnenberger
wrote:
> On Wed, Nov 19, 2014 at 04:58:08PM -0800, Peter Collingbourne wrote:
> > On Thu, Nov 20, 2014 at 12:19:06AM +0100, Joerg Sonnenberger wrote:
> > > On Wed, Nov 19, 2014 at 01:53:17PM -0800, Peter Collingbourne
wrote:
> > > > llgo depends on certain third-party components, namely a
copy of the Go
> > > > standard library (libgo), a Go program analysis library
(go.tools) and two
> > > > library dependencies of the standard library (libbacktrace
and libffi).
> > > 
> > > I think providing a better alternative to libffi is already a
goal of
> > > some people, but what is libbacktrace needed for? What is not
provided
> > > by the Itanium Unwind ABI?
> > 
> > According to the libbacktrace readme file:
> > 
> > > As of September 2012, libbacktrace only supports ELF executables
with
> > > DWARF debugging information.  The library is written to make it
> > > straightforward to add support for other object file and
debugging
> > > formats.
> 
> My question still stands. Do you use it for nice backtraces in debugging
> situations?
It appears so.

I did not write the code in libgo that deals with stack traces; Ian did. If
you have any other questions about this, it would be best to ask him.

Thanks,
-- 
Peter