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: Adrian Hunter adrian.hunter@intel.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/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; }