linux-kernel - [PATCH 1/2] perf probe: Fix to adjust symbol address with correct reloc

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Message-Id: <160027468295.803747.2704860727122011684.stgit@devnote2>
Date:   Thu, 17 Sep 2020 01:44:43 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:     "Frank Ch . Eigler" <fche@...hat.com>,
        Aaron Merey <amerey@...hat.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] perf probe: Fix to adjust symbol address with correct reloc_sym address

Perf probe uses ref_reloc_sym to adjust symbol offset address
from debuginfo address or ref_reloc_sym based address, but
that is misused the reloc_sym->addr and reloc_sym->unrelocated_addr.
If map is not relocated (map->reloc == 0), we can use reloc_sym->addr
as unrelocated address instead of reloc_sym->unrelocated_addr.

This usually may not happen. If we have a non-stripped elf
binary, we will use it for map and debuginfo, if not, we use only
kallsyms without debuginfo. Thus, the map is always relocated (elf
and dwarf binary) or not relocated (kallsyms).

However, if we will allow the combination of debuginfo and kallsyms
based map (like using debuginfod), we have to check the map->reloc
and choose the collect address of reloc_sym.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/probe-event.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 99d36ac77c08..17831f186ab5 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -129,9 +129,10 @@ static int kernel_get_symbol_address_by_name(const char *name, u64 *addr,
 	struct map *map;
 
 	/* ref_reloc_sym is just a label. Need a special fix*/
-	reloc_sym = kernel_get_ref_reloc_sym(NULL);
+	reloc_sym = kernel_get_ref_reloc_sym(&map);
 	if (reloc_sym && strcmp(name, reloc_sym->name) == 0)
-		*addr = (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
+		*addr = (!map->reloc || reloc) ? reloc_sym->addr :
+			reloc_sym->unrelocated_addr;
 	else {
 		sym = machine__find_kernel_symbol_by_name(host_machine, name, &map);
 		if (!sym)
@@ -795,7 +796,8 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
 			free(tevs[i].point.symbol);
 		tevs[i].point.symbol = tmp;
 		tevs[i].point.offset = tevs[i].point.address -
-				       reloc_sym->unrelocated_addr;
+			(map->reloc ? reloc_sym->unrelocated_addr :
+				      reloc_sym->addr);
 	}
 	return skipped;
 }