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

Arnaldo Carvalho de Melo
2022-03-17T15:37:11Z

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?

- 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