Re: [PATCH 1/2] xen: move CONFIG_DEBUG_INFO out of EXPERT section

[Juergen Gross <jgross@xxxxxxxx>]

On 07.03.23 12:42, Jan Beulich wrote:
> On 07.03.2023 12:33, Juergen Gross wrote:
> > On 07.03.23 11:31, Jan Beulich wrote:
> > > On 07.03.2023 07:32, Juergen Gross wrote:
> > > > Using a rather oldish gcc (7.5) it was verified that code generation
> > > > doesn't really differ between CONFIG_DEBUG_INFO on or off without
> > > > CONFIG_DEBUG being set (only observed differences were slightly
> > > > different symbol addresses, verified via "objdump -d"). The old gcc
> > > > version selection was based on the assumption, that newer gcc won't
> > > > regress in this regard.
> > > This is good to know, but I'm still curious about the mentioned
> > > differences in symbol addresses: If code generation didn't change, what
> > > caused addresses to differ? Is that merely because individual functions
> > > or objects are emitted in different order by the compiler? (If so I'd
> > > be inclined to infer that comparing generated code must have been
> > > quite a bit of effort, as first of all you would have had to undo that
> > > re-ordering.)
> > I did a simple diff of the two disassembly outputs and got only small
> > differences for %rip relative addresses (the differences were in the
> > range of +/- 32 bytes).
> That's still odd and hence imo wants understanding. Do you still have
> both binaries around?
I have just regenerated the one with debug-info. It is a 4.17 build.

I just found the at least one reason: xen_config_data has a different size
(obviously!) and this finally leads to an offset of 32 bytes for symbols
at higher addresses (with some items only differing by 8 bytes due to
alignment).


Juergen

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