Re: [PATCH v3] perf cs-etm: Improve completeness for kernel address space

From: Mathieu Poirier
Date: Mon Jul 08 2019 - 13:34:13 EST

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On Wed, 19 Jun 2019 at 21:45, Leo Yan <leo.yan@xxxxxxxxxx> wrote:
>
> 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 'etmq->etm->kernel_start', then can
> get a fixed up kernel start address which contain memory regions for
> device module and BPF. Finally, cs_etm__cpu_mode() can return right
> mode for these 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:
>
> - Build LLVM/Clang 8.0 or later version;
>
> - 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]"
> ffff000000086a84 t bpf_prog_f173133dc38ccf87_sys_enter [bpf]
> ffff000000088618 t bpf_prog_c1bd85c092d6e4aa_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/@20070000.etr/ \
> --filter 'filter 0xffff000000086a84/0x800' -a sleep 5s
>
> - Annotate for symbol 'bpf_prog_f173133dc38ccf87_sys_enter':
>
> root@debian:~# perf report
> Then select 'branches' samples and press 'a' to annotate symbol
> 'bpf_prog_f173133dc38ccf87_sys_enter', press 'P' to print to the
> bpf_prog_f173133dc38ccf87_sys_enter.annotation file:
>
> root@debian:~# cat bpf_prog_f173133dc38ccf87_sys_enter.annotation
>
> bpf_prog_f173133dc38ccf87_sys_enter() bpf_prog_f173133dc38ccf87_sys_enter
> Event: branches
>
> Percent int sys_enter(struct syscall_enter_args *args)
> stp x29, x30, [sp, #-16]!
>
> int key = 0;
> mov x29, sp
>
> augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
> stp x19, x20, [sp, #-16]!
>
> augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
> stp x21, x22, [sp, #-16]!
>
> stp x25, x26, [sp, #-16]!
>
> return bpf_get_current_pid_tgid();
> mov x25, sp
>
> return bpf_get_current_pid_tgid();
> mov x26, #0x0 // #0
>
> sub sp, sp, #0x10
>
> return bpf_map_lookup_elem(pids, &pid) != NULL;
> add x19, x0, #0x0
>
> mov x0, #0x0 // #0
>
> mov x10, #0xfffffffffffffff8 // #-8
>
> if (pid_filter__has(&pids_filtered, getpid()))
> str w0, [x25, x10]
>
> probe_read(&augmented_args->args, sizeof(augmented_args->args), args);
> add x1, x25, #0x0
>
> probe_read(&augmented_args->args, sizeof(augmented_args->args), args);
> mov x10, #0xfffffffffffffff8 // #-8
>
> syscall = bpf_map_lookup_elem(&syscalls, &augmented_args->args.syscall_nr);
> add x1, x1, x10
>
> syscall = bpf_map_lookup_elem(&syscalls, &augmented_args->args.syscall_nr);
> mov x0, #0xffff8009ffffffff // #-140694538682369
>
> movk x0, #0x6698, lsl #16
>
> movk x0, #0x3e00
>
> mov x10, #0xffffffffffff1040 // #-61376
>
> if (syscall == NULL || !syscall->enabled)
> movk x10, #0x1023, lsl #16
>
> if (syscall == NULL || !syscall->enabled)
> movk x10, #0x0, lsl #32
>
> loop_iter_first()
> 3.69 â blr bpf_prog_f173133dc38ccf87_sys_enter
> loop_iter_first()
> add x7, x0, #0x0
>
> loop_iter_first()
> add x20, x7, #0x0
>
> int size = probe_read_str(&augmented_filename->value, filename_len, filename_arg);
> mov x0, #0x1 // #1

I'm not sure all this information about annotation should be in the
changelog. This patch is about being able to decode traces that
executed outside the current kernel addresse range and as such simply
using "perf report" or "perf script" successfully is enough to test
this set. Any information that goes beyond that muddies the water.

>
> [...]
>
> 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: coresight@xxxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
> tools/perf/Makefile.config | 22 ++++++++++++++++++++++
> tools/perf/util/cs-etm.c | 19 ++++++++++++++++++-
> 2 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 51dd00f65709..a58cd5a43a98 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -418,6 +418,28 @@ ifdef CORESIGHT
> endif
> LDFLAGS += $(LIBOPENCSD_LDFLAGS)
> EXTLIBS += $(OPENCSDLIBS)
> + PRE_START_SIZE := 0
> + ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds),)
> + ifeq ($(SRCARCH),arm64)
> + # 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+$$8}' 2>/dev/null)
> + endif
> + ifeq ($(SRCARCH),arm)
> + # Extract info from lds:
> + # . = ((0xC0000000)) + 0x00208000;
> + # PRE_START_SIZE := 0x00208000
> + PRE_START_SIZE := $(shell egrep ' \. \= ${2}0x[0-9a-fA-F]+${2}' \
> + $(srctree)/arch/$(SRCARCH)/kernel/vmlinux.lds | \
> + sed -e 's/[(|)|.|=|+|<|;|-]//g' -e 's/ \+/ /g' -e 's/^[ \t]*//' | \
> + awk -F' ' '{printf "0x%x", $$2}' 2>/dev/null)
> + endif
> + endif
> + CFLAGS += -DARM_PRE_START_SIZE=$(PRE_START_SIZE)

It might be useful to do this for arm and arm64 regardless of
CoreSight but I'll let Arnaldo decide on this.

> $(call detected,CONFIG_LIBOPENCSD)
> ifdef CSTRACE_RAW
> CFLAGS += -DCS_DEBUG_RAW
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 0c7776b51045..5fa0be3a3904 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -613,10 +613,27 @@ static void cs_etm__free(struct perf_session *session)
> static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address)
> {
> struct machine *machine;
> + u64 fixup_kernel_start = 0;
>
> machine = etmq->etm->machine;
>
> - if (address >= etmq->etm->kernel_start) {
> + /*
> + * Since arm and arm64 specify some memory regions prior to
> + * 'kernel_start', kernel addresses can be less than 'kernel_start'.
> + *
> + * For arm architecture, 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.
> + *
> + * For arm64 architecture, 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.
> + */
> + fixup_kernel_start = etmq->etm->kernel_start - ARM_PRE_START_SIZE;
> +
> + if (address >= fixup_kernel_start) {
> if (machine__is_host(machine))
> return PERF_RECORD_MISC_KERNEL;
> else

Tested-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>

> --
> 2.17.1
>

Next message: Matthew Wilcox: "Re: [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free_space"
Previous message: Martin Blumenstingl: "[PATCH RFC v1 2/2] mmc: host: meson-mx-sdhc: new driver for the Amlogic Meson SDHC host"
Next in thread: Leo Yan: "Re: [PATCH v3] perf cs-etm: Improve completeness for kernel address space"
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