[PATCH] perf symbols: Don't split kernel symbols when using kallsyms
From: Wei Li
Date: Sun Sep 29 2019 - 08:24:55 EST
If there is ovelapping of vmlinux addresses with modules on a system,
the kernel symbols will be split to unique DSOs([kernel].N) when using
/proc/kallsyms, introduced by commit 2e538c4a1847 ("perf tools: Improve
kernel/modules symbol lookup").
When doing perf probe/report on such a system, it will fail in finding
symbol, as the symbol split process is after the map searching, and the
created maps can't be matched with name in kernel_get_module_map().
I think the split is confusing and not so useful when using [kernel].N
instead of the original ELF section names here. So remove the split
process when using /proc/kallsyms only.
On my arm32 system:
V2R7C00_HI1212-OSN9800 ~/liwei # ./perf probe -v -a printk
probe-definition(0): printk
symbol:printk file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
map_groups__set_modules_path_dir: cannot open /lib/modules/5.3.0-rc5+ dir
Problems setting modules path maps, continuing anyway...
No kprobe blacklist support, ignored
Failed to open cache(-1): /root/.debug/[kernel.kallsyms]/8eb36727183e955c790f0c7feb22d8306be7ce99/probes
Cache open error: -1
Looking at the vmlinux_path (8 entries long)
symsrc__init: cannot get elf header.
Could not open debuginfo. Try to use symbols.
Looking at the vmlinux_path (8 entries long)
symsrc__init: cannot get elf header.
Failed to open /proc/kcore. Note /proc/kcore requires CAP_SYS_RAWIO capability to access.
Using /proc/kallsyms for symbols
Failed to find symbol printk in kernel
Error: Failed to add events. Reason: No such file or directory (Code: -2)
V2R7C00_HI1212-OSN9800 ~/liwei # ./perf probe -F
vector_addrexcptn
vector_dabt
vector_fiq
vector_irq
vector_pabt
vector_rst
vector_und
V2R7C00_HI1212-OSN9800 ~/liwei # sort -u /proc/kallsyms | head -n 10
01df0000 t __vectors_start
01df1000 t __stubs_start
01df1004 t vector_rst
01df1020 t vector_irq
01df10a0 t vector_dabt
01df1120 t vector_pabt
01df11a0 t vector_und
01df1220 t vector_addrexcptn
01df1240 T vector_fiq
bf000000 t $a [eth]
V2R7C00_HI1212-OSN9800 ~/liwei # sort -u /proc/kallsyms | grep _stext -B 10
c1e04000 t swapper_pg_dir
c1e08000 T stext
c1e08000 t _text
c1e080b8 t __create_page_tables
c1e081bc t __fixup_smp
c1e08224 t __fixup_smp_on_up
c1e08240 t __fixup_pv_table
c1e082b0 t __vet_atags
c1e08300 T __turn_mmu_on
c1e08300 t __idmap_text_start
c1e08300 t _stext
V2R7C00_HI1212-OSN9800 ~/liwei # ./perf record -a sleep 2
Couldn't synthesize bpf events.
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.024 MB perf.data (140 samples) ]
V2R7C00_HI1212-OSN9800 ~/liwei # ./perf report
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 140 of event 'cycles'
# Event count (approx.): 9286809
#
# Overhead Command Shared Object Symbol
# ........ ....... ................. .................
#
15.89% swapper [unknown] [k] 0xc1e10b2c
7.83% swapper [unknown] [k] 0xc1e303f4
6.66% swapper [unknown] [k] 0xc1e84d58
6.28% sleep ld-2.27.so [.] do_lookup_x
6.07% swapper [unknown] [k] 0xc23f59dc
3.19% swapper [unknown] [k] 0xc23f0bfc
3.18% swapper [unknown] [k] 0xc2194d18
3.18% sleep libc-2.27.so [.] _dl_addr
3.17% sleep [unknown] [k] 0xc1e23454
3.16% sleep ld-2.27.so [.] check_match
3.12% sleep ld-2.27.so [.] strcmp
3.12% swapper [unknown] [k] 0xc1e52ce8
3.10% sleep [unknown] [k] 0xc1f738a4
3.08% sleep [unknown] [k] 0xc21a1ef8
3.05% sleep [unknown] [k] 0xc1f7109c
3.02% sleep [unknown] [k] 0xc1f59520
2.99% sleep [unknown] [k] 0xc23f54d4
...
Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
---
tools/perf/util/symbol.c | 54 ++++++----------------------------------
1 file changed, 7 insertions(+), 47 deletions(-)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 4efde7879474..1c0d6d0e4ed1 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -743,9 +743,7 @@ static int map_groups__split_kallsyms_for_kcore(struct map_groups *kmaps, struct
}
/*
- * Split the symbols into maps, making sure there are no overlaps, i.e. the
- * kernel range is broken in several maps, named [kernel].N, as we don't have
- * the original ELF section names vmlinux have.
+ * Remove module and useless symbols from the map derived from /proc/kallsyms.
*/
static int map_groups__split_kallsyms(struct map_groups *kmaps, struct dso *dso, u64 delta,
struct map *initial_map)
@@ -753,10 +751,9 @@ static int map_groups__split_kallsyms(struct map_groups *kmaps, struct dso *dso,
struct machine *machine;
struct map *curr_map = initial_map;
struct symbol *pos;
- int count = 0, moved = 0;
+ int moved = 0;
struct rb_root_cached *root = &dso->symbols;
struct rb_node *next = rb_first_cached(root);
- int kernel_range = 0;
bool x86_64;
if (!kmaps)
@@ -823,57 +820,20 @@ static int map_groups__split_kallsyms(struct map_groups *kmaps, struct dso *dso,
* symbols at this point.
*/
goto discard_symbol;
- } else if (curr_map != initial_map) {
- char dso_name[PATH_MAX];
- struct dso *ndso;
-
+ } else {
+ curr_map = initial_map;
if (delta) {
/* Kernel was relocated at boot time */
pos->start -= delta;
pos->end -= delta;
}
-
- if (count == 0) {
- curr_map = initial_map;
- goto add_symbol;
- }
-
- if (dso->kernel == DSO_TYPE_GUEST_KERNEL)
- snprintf(dso_name, sizeof(dso_name),
- "[guest.kernel].%d",
- kernel_range++);
- else
- snprintf(dso_name, sizeof(dso_name),
- "[kernel].%d",
- kernel_range++);
-
- ndso = dso__new(dso_name);
- if (ndso == NULL)
- return -1;
-
- ndso->kernel = dso->kernel;
-
- curr_map = map__new2(pos->start, ndso);
- if (curr_map == NULL) {
- dso__put(ndso);
- return -1;
- }
-
- curr_map->map_ip = curr_map->unmap_ip = identity__map_ip;
- map_groups__insert(kmaps, curr_map);
- ++kernel_range;
- } else if (delta) {
- /* Kernel was relocated at boot time */
- pos->start -= delta;
- pos->end -= delta;
}
-add_symbol:
+
if (curr_map != initial_map) {
rb_erase_cached(&pos->rb_node, root);
symbols__insert(&curr_map->dso->symbols, pos);
++moved;
- } else
- ++count;
+ }
continue;
discard_symbol:
@@ -887,7 +847,7 @@ static int map_groups__split_kallsyms(struct map_groups *kmaps, struct dso *dso,
dso__set_loaded(curr_map->dso);
}
- return count + moved;
+ return moved;
}
bool symbol__restricted_filename(const char *filename,
--
2.17.1