On Tue, May 17, 2016 at 03:45:34PM -0400, Jeff King wrote:

> Note that we set up f90, fa0, and fb0, but then pass fc0 into
> strbuf_write_column (and it has bogus color values). It looks like we're
> reading one past the end of our array, but I haven't figured out where
> or why.

Looking at the valgrind output reveals that. Here's an assert() that
catches it reliably for me:

diff --git a/graph.c b/graph.c
index 1350bdd..964bbd1 100644
--- a/graph.c
+++ b/graph.c
@@ -794,9 +794,11 @@ static int graph_draw_octopus_merge(struct git_graph 
*graph,
                ((graph->num_parents - dashless_commits) * 2) - 1;
        for (i = 0; i < num_dashes; i++) {
                col_num = (i / 2) + dashless_commits + graph->commit_index;
+               assert(col_num < graph->num_new_columns);
                strbuf_write_column(sb, &graph->new_columns[col_num], '-');
        }
        col_num = (i / 2) + dashless_commits + graph->commit_index;
+       assert(col_num < graph->num_new_columns);
        strbuf_write_column(sb, &graph->new_columns[col_num], '.');
        return num_dashes + 1;
 }

(It's actually the first one which triggers). I'm not familiar enough
with the code to know whether the col_num computation is bogus, or
whether we needed to earlier increase the size of the "new_columns"
field.

-Peff
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