Re: [PATCH v4 10/11] perf env: Set flag for kernel is 64-bit mode

From: Arnaldo Carvalho de Melo
Date: Wed Jul 14 2021 - 10:00:50 EST


Em Wed, Jul 14, 2021 at 10:59:49AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jul 13, 2021 at 05:31:03PM +0000, Hunter, Adrian escreveu:
> > > On Mon, Jul 12, 2021 at 03:14:35PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Sun, Jul 11, 2021 at 06:41:04PM +0800, Leo Yan escreveu:
> > > > > +++ b/tools/perf/util/env.c
> > > > > @@ -11,6 +11,7 @@
> > > > > #include <stdlib.h>
> > > > > #include <string.h>
>
> > > > > +int kernel_is_64_bit;
> > > > > struct perf_env perf_env;
>
> > > > Why can't this be in 'struct perf_env'?
>
> > > Good question. I considered to add it in struct perf_env but finally I used this
> > > way; the reason is this variable "kernel_is_64_bit" is only used during
> > > recording phase for AUX ring buffer, and don't use it for report. So seems to
> > > me it's over complexity to add a new field and just wander if it's necessary to
> > > save this field as new feature in the perf header.
>
> > I think we store the arch, so if the "kernel_is_64_bit" calculation depends only on arch
> > then I guess we don't need a new feature at the moment.
>
> So, I wasn't suggesting to add this info to the perf.data file header,
> just to the in-memory 'struct perf_env'.
>
> And also we should avoid unconditionally initializing things that we may
> never need, please structure it as:

Oops, forgot these:

> static void perf_env__init_kernel_mode(struct perf_env *env)
> {
> const char *arch = perf_env__raw_arch(env);
>
> if (!strncmp(arch, "x86_64", 6) || !strncmp(arch, "aarch64", 7) ||
> !strncmp(arch, "arm64", 5) || !strncmp(arch, "mips64", 6) ||
> !strncmp(arch, "parisc64", 8) || !strncmp(arch, "riscv64", 7) ||
> !strncmp(arch, "s390x", 5) || !strncmp(arch, "sparc64", 7))
> kernel_is_64_bit = 1;
env->kernel_is_64_bit = 1;
> else
> kernel_is_64_bit = 0;
env->kernel_is_64_bit = 0;
> }
>
>
> void perf_env__init(struct perf_env *env)
> {
> ...
> env->kernel_is_64_bit = -1;
> ...
> }
>
> bool perf_env__kernel_is_64_bit(struct perf_env *env)
> {
> if (env->kernel_is_64_bit == -1)
> perf_env__init_kernel_mode(env);
>
> return env->kernel_is_64_bit;
> }
>
> One thing in my TODO is to crack down on the tons of initializations
> perf does unconditionally, last time I looked there are lots :-\
>
> - Arnaldo
>
> > > Combining the comment from Adrian in another email, I think it's good to add
> > > a new field "compat_mode" in the struct perf_env, and this field will be
> > > initialized in build-record.c. Currently we don't need to save this value into
> > > the perf file, if later we need to use this value for decoding phase, then we
> > > can add a new feature item to save "compat_mode"
> > > into the perf file's header.
>
> > > If you have any different idea, please let me know. Thanks!

--

- Arnaldo