Re: [PATCH 12/12] perf maps: Set maps pointer in the kmap area for kernel maps

Arnaldo Carvalho de Melo
2019-12-18T19:01:26Z

Em Wed, Dec 18, 2019 at 03:22:54PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Wed, Dec 18, 2019 at 10:05:04AM +0100, Jiri Olsa escreveu:
> After looking at this some more, I retract this patch and instead the
> two-liner at the end of this message seems enough.

So here is the full cset, I have not made changes to the other patches,

- Arnaldo

commit 178427a192bcbe3ad93dd0637c3dceaa3ccef31e
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date: Wed Dec 18 15:23:14 2019 -0300

perf map: Set kmap->kmaps backpointer for main kernel map chunks

When a map is create to represent the main kernel area (vmlinux) with
map__new2() we allocate an extra area to store a pointer to the 'struct
maps' for the kernel maps, so that we can access that struct when
loading ELF files or kallsyms, as we will need to split it in multiple
maps, one per kernel module or ELF section (such as ".init.text").

So when map->dso->kernel is non-zero, it is expected that
map__kmap(map)->kmaps to be set to the tree of kernel maps (modules,
chunks of the main kernel, bpf progs put in place via
PERF_RECORD_KSYMBOL, the main kernel).

This was not the case when we were splitting the main kernel into chunks
for its ELF sections, which ended up making 'perf report --children'
processing a perf.data file with callchains to trip on
__map__is_kernel(), when we press ENTER to see the popup menu for main
histogram entries that starts at a symbol in the ".init.text" ELF
section, e.g.:

- 8.83% 0.00% swapper [kernel.vmlinux].init.text [k] start_kernel
start_kernel
cpu_startup_entry
do_idle
cpuidle_enter
cpuidle_enter_state
intel_idle

Fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-vcokue57w4goyzweg2rr5i80@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 6658fbf196e6..1965aefccb02 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -920,6 +920,9 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
if (curr_map == NULL)
return -1;

+ if (curr_dso->kernel)
+ map__kmap(curr_map)->kmaps = kmaps;
+
if (adjust_kernel_syms) {
curr_map->start = shdr->sh_addr + ref_reloc(kmap);
curr_map->end = curr_map->start + shdr->sh_size;