Re: [PATCH v4 1/2] perf machine: Support arch's specific kernel start address

[Leo Yan]

On Mon, Aug 12, 2019 at 09:37:33AM +0300, Adrian Hunter wrote:
> On 10/08/19 10:21 AM, Leo Yan wrote:
> > machine__get_kernel_start() gives out the kernel start address; some
> > architectures need to tweak the start address so that can reflect the
> > kernel start address correctly.  This is not only for x86_64 arch, but
> > it is also required by other architectures, e.g. arm/arm64 needs to
> > tweak the kernel start address so can include the kernel memory regions
> > which are used before the '_stext' symbol.
> > 
> > This patch refactors machine__get_kernel_start() by adding a weak
> > arch__fix_kernel_text_start(), any architecture can implement it to
> > tweak its specific start address; this also allows the arch specific
> > code to be placed into 'arch' folder.
> > 
> > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > ---
> >  tools/perf/arch/x86/util/machine.c | 10 ++++++++++
> >  tools/perf/util/machine.c          | 13 +++++++------
> >  tools/perf/util/machine.h          |  2 ++
> >  3 files changed, 19 insertions(+), 6 deletions(-)
> > 
> > diff --git a/tools/perf/arch/x86/util/machine.c b/tools/perf/arch/x86/util/machine.c
> > index 1e9ec783b9a1..9f012131534a 100644
> > --- a/tools/perf/arch/x86/util/machine.c
> > +++ b/tools/perf/arch/x86/util/machine.c
> > @@ -101,4 +101,14 @@ int machine__create_extra_kernel_maps(struct machine *machine,
> >  	return ret;
> >  }
> >  
> > +void arch__fix_kernel_text_start(u64 *start)
> > +{
> > +	/*
> > +	 * 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.
> > +	 */
> > +	*start = 1ULL << 63;
> > +}
> 
> That is needed for reporting x86 data on any arch i.e. it is not specific to
> the compile-time architecture, it is specific to the perf.data file
> architecture, which is what machine__is() compares. So, this looks wrong.

Thanks for reviewing, Adrian.

If so, I think we should extend the function machine__get_kernel_start()
as below; for building successfully, will always define the macro
ARM_PRE_START_SIZE in Makefile.config.

@Arnaldo, @Adrian, Please let me know if this works for you?

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index f6ee7fbad3e4..30a0ff627263 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, some memory regions are prior to '_stext'
+                * symbol; to reflect the complete kernel address space,
+                * compensate these pre-defined regions for kernel start
+                * address.
+                */
+               if (machine__is(machine, "arm64") ||
+                   machine__is(machine, "arm"))
+                       machine->kernel_start -= ARM_PRE_START_SIZE;
        }
        return err;
 }

Thanks,
Leo Yan

> > +
> >  #endif
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index f6ee7fbad3e4..603518835692 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -2671,6 +2671,10 @@ int machine__nr_cpus_avail(struct machine *machine)
> >  	return machine ? perf_env__nr_cpus_avail(machine->env) : 0;
> >  }
> >  
> > +void __weak arch__fix_kernel_text_start(u64 *start __maybe_unused)
> > +{
> > +}
> > +
> >  int machine__get_kernel_start(struct machine *machine)
> >  {
> >  	struct map *map = machine__kernel_map(machine);
> > @@ -2687,14 +2691,11 @@ int machine__get_kernel_start(struct machine *machine)
> >  	machine->kernel_start = 1ULL << 63;
> >  	if (map) {
> >  		err = map__load(map);
> > -		/*
> > -		 * 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 (!err)
> >  			machine->kernel_start = map->start;
> >  	}
> > +
> > +	arch__fix_kernel_text_start(&machine->kernel_start);
> >  	return err;
> >  }
> >  
> > diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> > index ef803f08ae12..9cb459f4bfbc 100644
> > --- a/tools/perf/util/machine.h
> > +++ b/tools/perf/util/machine.h
> > @@ -278,6 +278,8 @@ void machine__get_kallsyms_filename(struct machine *machine, char *buf,
> >  int machine__create_extra_kernel_maps(struct machine *machine,
> >  				      struct dso *kernel);
> >  
> > +void arch__fix_kernel_text_start(u64 *start);
> > +
> >  /* Kernel-space maps for symbols that are outside the main kernel map and module maps */
> >  struct extra_kernel_map {
> >  	u64 start;
> > 
>