[PATCH v5] perf machine: arm/arm64: Improve completeness for kernel address space

From: Leo Yan
Date: Thu Aug 15 2019 - 04:25:49 EST

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Arm and arm64 architecture reserve some memory regions prior to the
symbol '_stext' and these memory regions later will be used by device
module and BPF jit. The current code misses to consider these memory
regions thus any address in the regions will be taken as user space
mode, but perf cannot find the corresponding dso with the wrong CPU
mode so we misses to generate samples for device module and BPF
related trace data.

This patch parse the link scripts to get the memory size prior to start
address and reduce this size from 'machine>->kernel_start', then can
get a fixed up kernel start address which contain memory regions for
device module and BPF. Finally, machine__get_kernel_start() can reflect
more complete kernel memory regions and perf can successfully generate
samples.

The reason for parsing the link scripts is Arm architecture changes text
offset dependent on different platforms, which define multiple text
offsets in $kernel/arch/arm/Makefile. This offset is decided when build
kernel and the final value is extended in the link script, so we can
extract the used value from the link script. We use the same way to
parse arm64 link script as well. If fail to find the link script, the
pre start memory size is assumed as zero, in this case it has no any
change caused with this patch.

Below is detailed info for testing this patch:

- Install or build LLVM/Clang;

- Configure perf with ~/.perfconfig:

root@debian:~# cat ~/.perfconfig
# this file is auto-generated.
[llvm]
clang-path = /mnt/build/llvm-build/build/install/bin/clang
kbuild-dir = /mnt/linux-kernel/linux-cs-dev/
clang-opt = "-g"
dump-obj = true

[trace]
show_zeros = yes
show_duration = no
no_inherit = yes
show_timestamp = no
show_arg_names = no
args_alignment = 40
show_prefix = yes

- Run 'perf trace' command with eBPF event:

root@debian:~# perf trace -e string \
-e $kernel/tools/perf/examples/bpf/augmented_raw_syscalls.c

- Read eBPF program memory mapping in kernel:

root@debian:~# echo 1 > /proc/sys/net/core/bpf_jit_kallsyms
root@debian:~# cat /proc/kallsyms | grep -E "bpf_prog_.+_sys_[enter|exit]"
ffff00000008a0d0 t bpf_prog_e470211b846088d5_sys_enter [bpf]
ffff00000008c6a4 t bpf_prog_29c7ae234d79bd5c_sys_exit [bpf]

- Launch any program which accesses file system frequently so can hit
the system calls trace flow with eBPF event;

- Capture CoreSight trace data with filtering eBPF program:

root@debian:~# perf record -e cs_etm/@tmc_etr0/ \
--filter 'filter 0xffff00000008a0d0/0x800' -a sleep 5s

- Decode the eBPF program symbol 'bpf_prog_f173133dc38ccf87_sys_enter':

root@debian:~# perf script -F,ip,sym
Frame deformatter: Found 4 FSYNCS
0 [unknown]
ffff00000008a1ac bpf_prog_e470211b846088d5_sys_enter
ffff00000008a250 bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a124 bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a14c bpf_prog_e470211b846088d5_sys_enter
ffff00000008a13c bpf_prog_e470211b846088d5_sys_enter
ffff00000008a14c bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a180 bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a1ac bpf_prog_e470211b846088d5_sys_enter
ffff00000008a190 bpf_prog_e470211b846088d5_sys_enter
ffff00000008a1ac bpf_prog_e470211b846088d5_sys_enter
ffff00000008a250 bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a124 bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a14c bpf_prog_e470211b846088d5_sys_enter
0 [unknown]
ffff00000008a180 bpf_prog_e470211b846088d5_sys_enter
[...]

Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Suzuki Poulouse <suzuki.poulose@xxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: coresight@xxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
tools/perf/Makefile.config | 22 ++++++++++++++++++++++
tools/perf/util/machine.c | 15 ++++++++++++++-
2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index e4988f49ea79..d7ff839d8b20 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -48,9 +48,20 @@ ifeq ($(SRCARCH),x86)
NO_PERF_REGS := 0
endif

+ARM_PRE_START_SIZE := 0
+
ifeq ($(SRCARCH),arm)
NO_PERF_REGS := 0
LIBUNWIND_LIBS = -lunwind -lunwind-arm
+ ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds),)
+ # Extract info from lds:
+ # . = ((0xC0000000)) + 0x00208000;
+ # ARM_PRE_START_SIZE := 0x00208000
+ ARM_PRE_START_SIZE := $(shell egrep ' \. \= ${2}0x[0-9a-fA-F]+${2}' \
+ $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds | \
+ sed -e 's/[(|)|.|=|+|<|;|-]//g' -e 's/ \+/ /g' -e 's/^[ \t]*//' | \
+ awk -F' ' '{printf "0x%x", $$2}' 2>/dev/null)
+ endif
endif

ifeq ($(SRCARCH),arm64)
@@ -58,8 +69,19 @@ ifeq ($(SRCARCH),arm64)
NO_SYSCALL_TABLE := 0
CFLAGS += -I$(OUTPUT)arch/arm64/include/generated
LIBUNWIND_LIBS = -lunwind -lunwind-aarch64
+ ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds),)
+ # Extract info from lds:
+ # . = ((((((((0xffffffffffffffff)) - (((1)) << (48)) + 1) + (0)) + (0x08000000))) + (0x08000000))) + 0x00080000;
+ # ARM_PRE_START_SIZE := (0x08000000 + 0x08000000 + 0x00080000) = 0x10080000
+ ARM_PRE_START_SIZE := $(shell egrep ' \. \= ${8}0x[0-9a-fA-F]+${2}' \
+ $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds | \
+ sed -e 's/[(|)|.|=|+|<|;|-]//g' -e 's/ \+/ /g' -e 's/^[ \t]*//' | \
+ awk -F' ' '{printf "0x%x", $$6+$$7+$$8}' 2>/dev/null)
+ endif
endif

+CFLAGS += -DARM_PRE_START_SIZE=$(ARM_PRE_START_SIZE)
+
ifeq ($(SRCARCH),csky)
NO_PERF_REGS := 0
endif
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index f6ee7fbad3e4..e993f891bb82 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -2687,13 +2687,26 @@ int machine__get_kernel_start(struct machine *machine)
machine->kernel_start = 1ULL << 63;
if (map) {
err = map__load(map);
+ if (err)
+ return err;
+
/*
* On x86_64, PTI entry trampolines are less than the
* start of kernel text, but still above 2^63. So leave
* kernel_start = 1ULL << 63 for x86_64.
*/
- if (!err && !machine__is(machine, "x86_64"))
+ if (!machine__is(machine, "x86_64"))
machine->kernel_start = map->start;
+
+ /*
+ * On arm/arm64, the kernel uses some memory regions which are
+ * prior to '_stext' symbol; to reflect the complete kernel
+ * address space, compensate these pre-defined regions for
+ * kernel start address.
+ */
+ if (!strcmp(perf_env__arch(machine->env), "arm") ||
+ !strcmp(perf_env__arch(machine->env), "arm64"))
+ machine->kernel_start -= ARM_PRE_START_SIZE;
}
return err;
}
--
2.17.1

Next message: Tony Lindgren: "[PATCHv2] USB: serial: option: Add Motorola modem UARTs"
Previous message: Sakari Ailus: "Re: [PATCH v8 05/14] media: rkisp1: add Rockchip ISP1 subdev driver"
Next in thread: Adrian Hunter: "Re: [PATCH v5] perf machine: arm/arm64: Improve completeness for kernel address space"
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