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Subject[PATCH v4 2/2] perf machine: arm/arm64: Improve completeness for kernel address space
Date
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@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
tools/perf/Makefile.config | 22 ++++++++++++++++++++++
tools/perf/arch/arm/util/Build | 2 ++
tools/perf/arch/arm/util/machine.c | 17 +++++++++++++++++
tools/perf/arch/arm64/util/Build | 1 +
tools/perf/arch/arm64/util/machine.c | 17 +++++++++++++++++
5 files changed, 59 insertions(+)
create mode 100644 tools/perf/arch/arm/util/machine.c
create mode 100644 tools/perf/arch/arm64/util/machine.c

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index e4988f49ea79..76e0ad0b4fd2 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -51,6 +51,17 @@ endif
ifeq ($(SRCARCH),arm)
NO_PERF_REGS := 0
LIBUNWIND_LIBS = -lunwind -lunwind-arm
+ PRE_START_SIZE := 0
+ ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds),)
+ # Extract info from lds:
+ # . = ((0xC0000000)) + 0x00208000;
+ # PRE_START_SIZE := 0x00208000
+ 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
+ CFLAGS += -DARM_PRE_START_SIZE=$(PRE_START_SIZE)
endif

ifeq ($(SRCARCH),arm64)
@@ -58,6 +69,17 @@ ifeq ($(SRCARCH),arm64)
NO_SYSCALL_TABLE := 0
CFLAGS += -I$(OUTPUT)arch/arm64/include/generated
LIBUNWIND_LIBS = -lunwind -lunwind-aarch64
+ PRE_START_SIZE := 0
+ ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds),)
+ # Extract info from lds:
+ # . = ((((((((0xffffffffffffffff)) - (((1)) << (48)) + 1) + (0)) + (0x08000000))) + (0x08000000))) + 0x00080000;
+ # PRE_START_SIZE := (0x08000000 + 0x08000000 + 0x00080000) = 0x10080000
+ 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
+ CFLAGS += -DARM_PRE_START_SIZE=$(PRE_START_SIZE)
endif

ifeq ($(SRCARCH),csky)
diff --git a/tools/perf/arch/arm/util/Build b/tools/perf/arch/arm/util/Build
index 296f0eac5e18..efa6b768218a 100644
--- a/tools/perf/arch/arm/util/Build
+++ b/tools/perf/arch/arm/util/Build
@@ -1,3 +1,5 @@
+perf-y += machine.o
+
perf-$(CONFIG_DWARF) += dwarf-regs.o

perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
diff --git a/tools/perf/arch/arm/util/machine.c b/tools/perf/arch/arm/util/machine.c
new file mode 100644
index 000000000000..db172894e4ea
--- /dev/null
+++ b/tools/perf/arch/arm/util/machine.c
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/string.h>
+#include <stdlib.h>
+
+#include "../../util/machine.h"
+
+void arch__fix_kernel_text_start(u64 *start)
+{
+ /*
+ * On arm, the 16MB virtual memory space prior to 'kernel_start' is
+ * allocated to device modules, a PMD table if CONFIG_HIGHMEM is
+ * enabled and a PGD table. To reflect the complete kernel address
+ * space, compensate the pre-defined regions for kernel start address.
+ */
+ *start = *start - ARM_PRE_START_SIZE;
+}
diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
index 3cde540d2fcf..8081fb8a7b3d 100644
--- a/tools/perf/arch/arm64/util/Build
+++ b/tools/perf/arch/arm64/util/Build
@@ -1,4 +1,5 @@
perf-y += header.o
+perf-y += machine.o
perf-y += sym-handling.o
perf-$(CONFIG_DWARF) += dwarf-regs.o
perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
diff --git a/tools/perf/arch/arm64/util/machine.c b/tools/perf/arch/arm64/util/machine.c
new file mode 100644
index 000000000000..61058dca8c5a
--- /dev/null
+++ b/tools/perf/arch/arm64/util/machine.c
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/string.h>
+#include <stdlib.h>
+
+#include "../../util/machine.h"
+
+void arch__fix_kernel_text_start(u64 *start)
+{
+ /*
+ * On arm64, the root PGD table, device module memory region and
+ * BPF jit region are prior to 'kernel_start'. To reflect the
+ * complete kernel address space, compensate these pre-defined
+ * regions for kernel start address.
+ */
+ *start = *start - ARM_PRE_START_SIZE;
+}
--
2.17.1
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