linux-kernel - [PATCH 5.16 34/37] perf symbols: Fix symbol size calculation condition

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Date:   Mon, 21 Mar 2022 14:53:16 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michael Petlan <mpetlan@...hat.com>,
        Athira Jajeev <atrajeev@...ux.vnet.ibm.com>,
        Jiri Olsa <jolsa@...nel.org>, Kajol Jain <kjain@...ux.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 5.16 34/37] perf symbols: Fix symbol size calculation condition

From: Michael Petlan <mpetlan@...hat.com>

commit 3cf6a32f3f2a45944dd5be5c6ac4deb46bcd3bee upstream.

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.

Fixes: 3b01a413c196c910 ("perf symbols: Improve kallsyms symbol end addr calculation")
Signed-off-by: Michael Petlan <mpetlan@...hat.com>
Cc: Athira Jajeev <atrajeev@...ux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Kajol Jain <kjain@...ux.ibm.com>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
Link: http://lore.kernel.org/lkml/20220317135536.805-1-mpetlan@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/perf/util/symbol.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -231,7 +231,7 @@ void symbols__fixup_end(struct rb_root_c
 		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);
 	}