Re: [PATCH] perf symbols: Fix symbol size calculation condition

Michael Petlan
2022-03-17T17:49:51Z

On Thu, 17 Mar 2022, Arnaldo Carvalho de Melo wrote:
> Em Thu, Mar 17, 2022 at 02:55:36PM +0100, Michael Petlan escreveu:
> > Before this patch, the symbol end address fixup to be called, needed two
> > conditions being met:
> >
> > if (prev->end == prev->start && prev->end != curr->start)
> >
> > Where
> > "prev->end == prev->start" means that prev is zero-long
> > (and thus needs a fixup)
> > and
> > "prev->end != curr->start" means that fixup hasn't been applied yet
> >
> > However, this logic is incorrect in the following situation:
> >
> > *curr = {rb_node = {__rb_parent_color = 278218928,
> > rb_right = 0x0, rb_left = 0x0},
> > start = 0xc000000000062354,
> > end = 0xc000000000062354, namelen = 40, type = 2 '\002',
> > binding = 0 '\000', idle = 0 '\000', ignore = 0 '\000',
> > inlined = 0 '\000', arch_sym = 0 '\000', annotate2 = false,
> > name = 0x1159739e "kprobe_optinsn_page\t[__builtin__kprobes]"}
> >
> > *prev = {rb_node = {__rb_parent_color = 278219041,
> > rb_right = 0x109548b0, rb_left = 0x109547c0},
> > start = 0xc000000000062354,
> > end = 0xc000000000062354, namelen = 12, type = 2 '\002',
> > binding = 1 '\001', idle = 0 '\000', ignore = 0 '\000',
> > inlined = 0 '\000', arch_sym = 0 '\000', annotate2 = false,
> > name = 0x1095486e "optinsn_slot"}
> >
> > In this case, prev->start == prev->end == curr->start == curr->end,
> > thus the condition above thinks that "we need a fixup due to zero
> > length of prev symbol, but it has been probably done, since the
> > prev->end == curr->start", which is wrong.
> >
> > After the patch, the execution path proceeds to arch__symbols__fixup_end
> > function which fixes up the size of prev symbol by adding page_size to
> > its end offset.
>
> You missed this:
>
> Fixes: 3b01a413c196c910 ("perf symbols: Improve kallsyms symbol end addr calculation")
>
> I'll add it to the patch, ok?

Sure thing. Thanks.
M

>
> - Arnaldo
>
> > Signed-off-by: Michael Petlan <mpetlan@redhat.com>
> > ---
> > tools/perf/util/symbol.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index fb075aa8f8f2..dea0fc495185 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -231,7 +231,7 @@ void symbols__fixup_end(struct rb_root_cached *symbols)
> > prev = curr;
> > curr = rb_entry(nd, struct symbol, rb_node);
> >
> > - if (prev->end == prev->start && prev->end != curr->start)
> > + if (prev->end == prev->start || prev->end != curr->start)
> > arch__symbols__fixup_end(prev, curr);
> > }
> >
> > --
> > 2.18.4
>
> --
>
> - Arnaldo
>
>