On 15/08/19 2:32 PM, Leo Yan wrote:
Hi Adrian,
On Thu, Aug 15, 2019 at 11:54:54AM +0300, Adrian Hunter wrote:
[...]
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
So, that is not going to work if you take a perf.data file to a non-arm machine?
Yeah, this patch will only allow perf to work correctly when perf run natively on arm/arm64, so it can resolve partial of the issue.
How come you cannot use kallsyms to get the information?
Thanks for pointing out this. Sorry I skipped your comment "I don't know how you intend to calculate ARM_PRE_START_SIZE" when you reviewed the patch v3, I should use that chance to elaborate the detailed idea and so can get more feedback/guidance before procceed.
Actually, I have considered to use kallsyms when worked on the previous patch set.
As mentioned in patch set v4's cover letter, I tried to implement machine__create_extra_kernel_maps() for arm/arm64, the purpose is to parse kallsyms so can find more kernel maps and thus also can fixup the kernel start address. But I found the 'perf script' tool directly calls machine__get_kernel_start() instead of running into the flow for machine__create_extra_kernel_maps();
Doesn't it just need to loop through each kernel map to find the lowest start address?
so I finally gave up to usemachine__create_extra_kernel_maps() for tweaking kernel start address and went back to use this patch's approach by parsing lds files.
So for next step, I want to get some guidances:
One method is to add a new weak function, e.g. arch__fix_kernel_text_start(), then every arch can implement its own function to fixup the kernel start address;
For arm/arm64, can use kallsyms to find the symbols with least address and fixup for kernel start address.
Another method is to directly parse kallsyms in the function machine__get_kernel_start(), thus the change can be used for all archs;
Seems to me the second method is to address this issue as a common issue crossing all archs. But not sure if this is the requirement for all archs or just this is only required for arm/arm64. Please let me know what's your preference or other thoughts. Thanks a lot!
Leo.
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;}