Messages in this thread | ![/](/images/icornerl.gif) | | From | Ravi Bangoria <> | Subject | [RFC 0/4] perf tool: Fix non-".text" symbol resolution for kernel modules | Date | Tue, 10 Jan 2023 11:28:55 +0530 |
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Kernel module elf contains executable code in non-".text" sections as well, for ex: ".noinstr.text". Plus, kernel module's memory layout differs from it's binary layout because .ko elf does not contain program header table.
Perf tries to solve it by creating special maps for allocated (SHF_ALLOC) elf sections, but perf uses elf addresses for map address range and thus these special maps remains unused because no real ip falls into their address range.
Solve this by preparing section specific special maps using addresses provided by sysfs /sys/module/.../sections/. Also save these details in PERF_RECORD_KMOD_SEC_MAP format in perf.data which can be consumed at perf-report time.
Without patchset:
# perf record -a -c 5000000 # perf report Overhead Command Shared Object Symbol 13.20% qemu-system-x86 [unknown] [.] 0x00005557527b1973 6.58% qemu-system-x86 [kvm_amd] [k] 0x00000000000151e6 6.36% qemu-system-x86 [kernel.vmlinux] [k] native_load_gdt 6.21% qemu-system-x86 [kernel.vmlinux] [k] native_load_tr_desc 4.71% qemu-system-x86 [kvm] [k] vcpu_run 4.52% qemu-system-x86 [kvm_amd] [k] svm_vcpu_run 3.50% qemu-system-x86 [kvm] [k] kvm_cpuid 2.09% qemu-system-x86 [kvm] [k] kvm_pmu_trigger_event 1.98% qemu-system-x86 [kvm_amd] [k] 0x0000000000015171 1.05% qemu-system-x86 [kvm_amd] [k] svm_handle_exit 1.04% qemu-system-x86 [kvm_amd] [k] 0x00000000000151e2 0.94% qemu-system-x86 [kvm_amd] [k] 0x0000000000015174
Same perf.data with kallsyms:
# perf report --kallsyms=/proc/kallsyms Overhead Command Shared Object Symbol 14.22% qemu-system-x86 [kvm_amd] [k] __svm_vcpu_run 13.20% qemu-system-x86 [unknown] [.] 0x00005557527b1973 6.36% qemu-system-x86 [kernel.vmlinux] [k] native_load_gdt 6.21% qemu-system-x86 [kernel.vmlinux] [k] native_load_tr_desc 4.71% qemu-system-x86 [kvm] [k] vcpu_run 4.52% qemu-system-x86 [kvm_amd] [k] svm_vcpu_run 3.50% qemu-system-x86 [kvm] [k] kvm_cpuid 2.09% qemu-system-x86 [kvm] [k] kvm_pmu_trigger_event 1.05% qemu-system-x86 [kvm_amd] [k] svm_handle_exit
With patchset:
# perf record -a -c 5000000 # perf report Overhead Command Shared Object Symbol 13.44% qemu-system-x86 [kvm-amd].noinstr.text [k] __svm_vcpu_run 13.25% qemu-system-x86 [unknown] [.] 0x000055f4c6563973 7.13% qemu-system-x86 [kernel.vmlinux] [k] native_load_gdt 6.00% qemu-system-x86 [kernel.vmlinux] [k] native_load_tr_desc 5.13% qemu-system-x86 [kvm_amd] [k] svm_vcpu_run 4.83% qemu-system-x86 [kvm] [k] vcpu_run 3.65% qemu-system-x86 [kvm] [k] kvm_cpuid
Same perf.data with kallsyms:
# perf report --kallsyms=/proc/kallsyms Overhead Command Shared Object Symbol 13.44% qemu-system-x86 [kernel.vmlinux] [k] __svm_vcpu_run 13.25% qemu-system-x86 [unknown] [.] 0x000055f4c6563973 7.13% qemu-system-x86 [kernel.vmlinux] [k] native_load_gdt 6.00% qemu-system-x86 [kernel.vmlinux] [k] native_load_tr_desc 5.13% qemu-system-x86 [kernel.vmlinux] [k] svm_vcpu_run 4.83% qemu-system-x86 [kernel.vmlinux] [k] vcpu_run 3.65% qemu-system-x86 [kernel.vmlinux] [k] kvm_cpuid
This is an RFC only series. TODOs: - I'm just recording module path in PERF_RECORD_KMOD_SEC_MAP. It's very much possible that, at perf report time, a module file exists at the same path but it's internal layout is different. I think I need to add some buildid check. Any ideas? - I've enabled host perf-record/report only. It doesn't work for guest modules because host does not have access to guest sysfs. I'm yet to figure out how to fix it. May be we can add --guest-mod-sysfs option. Any ideas? - Also, I'm currently assuming that module files are not compressed. - I've seen perf build failures when compiling with NO_LIBELF=1. - I've seen perf report not honoring --kallsyms in certain conditions.
Prepared on top of acme/perf/core (69b41ac87e4a6)
Ravi Bangoria (4): perf tool: Simplify machine__create_modules() a bit perf tool: Refactor perf_event__synthesize_modules() perf tool: Introduce PERF_RECORD_KMOD_SEC_MAP perf tool: Fix non-".text" symbol resolution for kernel modules
tools/lib/perf/Documentation/libperf.txt | 1 + tools/lib/perf/include/perf/event.h | 25 +++ tools/perf/builtin-annotate.c | 1 + tools/perf/builtin-c2c.c | 1 + tools/perf/builtin-diff.c | 1 + tools/perf/builtin-inject.c | 1 + tools/perf/builtin-kmem.c | 1 + tools/perf/builtin-mem.c | 1 + tools/perf/builtin-record.c | 14 ++ tools/perf/builtin-report.c | 1 + tools/perf/builtin-script.c | 13 ++ tools/perf/builtin-trace.c | 1 + tools/perf/util/build-id.c | 1 + tools/perf/util/data-convert-bt.c | 1 + tools/perf/util/data-convert-json.c | 1 + tools/perf/util/event.c | 22 ++ tools/perf/util/event.h | 5 + tools/perf/util/machine.c | 268 ++++++++++++++++++++++- tools/perf/util/machine.h | 2 + tools/perf/util/map.c | 1 + tools/perf/util/map.h | 4 + tools/perf/util/session.c | 17 ++ tools/perf/util/symbol-elf.c | 9 +- tools/perf/util/symbol.c | 2 +- tools/perf/util/synthetic-events.c | 136 +++++++++--- tools/perf/util/tool.h | 3 +- 26 files changed, 494 insertions(+), 39 deletions(-)
-- 2.39.0
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