On Mon, Feb 26, 2018 at 08:26:10AM +0100, Julia Lawall wrote:
>
>
> On Sun, 25 Feb 2018, frowand.list@xxxxxxxxx wrote:
>
> > From: Frank Rowand <frank.rowand@xxxxxxxx>
> >
> > From: Frank Rowand <frowand.list@xxxxxxxxx>
> >
> > Signed-off-by: Frank Rowand <frowand.list@xxxxxxxxx>
> > ---
> >
> > This patch does not work.
> >
> > After applying this patch, I get a syntax error when I try to
> > compile a devicetree source with a label on the root node:
> >
> > $ dtc -O dts junk_lab.dts >junk
> > Error: junk_lab.dts:3.9-10 syntax error
> > FATAL ERROR: Unable to parse input tree
>
> You have some shift reduce conflicts. It is making a choice that is
> diffeernt than what you expect. The problem seems to be with memreserves.
> That comes just before a devicetree and can also start with a DT_LABEL, so
> when it sees a DT_LABEL, it doesn't know if it is for memreserves or for
> devicetree.
>
> I figured this out using bison --verbose dtc-parser.y. This gives you a
> dtc-parser.output file. But no one likes looking at these...
Ah, thanks for the analysis Julia. I was guessing we had a parser
conflict at play here, but hadn't had a chance to investigate. Frank
if you see errors from Bison during the build, that's generally not
something you should ignore..
So, you could probably fix this by adding the Bison %glr-parser
option. We used to have that, but we managed to re-arrange the
grammar to avoid it, which gives us wider parser generator
compatibility.
As Julia says, the problem is roughly that when the parser sees a
label it doesn't know if a memreserve or the root node is eventually
going to follow it, so it doesn't know which branch of the grammar to
go down.
In a bit more detail, without %glr-parser, Bison generates a LALR(1)
parser. That means the parser is able to look ahead 1 token to work
out what rules to use. Because you can have multiple labels before
either a memreserve or the root node with your grammar, 1 token isn't
enough - there could be an arbitrary number of tokens before it sees
either the '/memreserve/' or '/' tokens which let it know which way to
go.
>
> julia
>
> >
> >
> >
> > dtc-parser.y | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/dtc-parser.y b/dtc-parser.y
> > index 44af170abfea..821dba228d79 100644
> > --- a/dtc-parser.y
> > +++ b/dtc-parser.y
> > @@ -162,6 +162,11 @@ devicetree:
> > {
> > $$ = name_node($2, "");
> > }
> > + | DT_LABEL devicetree
> > + {
> > + add_label(&$2->labels, $1);
> > + $$ = $2;
> > + }
> > | devicetree '/' nodedef
> > {
> > $$ = merge_nodes($1, $3);
> >
> >
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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