Re: [PATCH] perf tools: Support bpf prologue for arm64

From: Will Deacon
Date: Wed Sep 02 2015 - 06:35:06 EST


On Mon, Aug 31, 2015 at 09:16:28PM +0100, Arnaldo Carvalho de Melo wrote:
> Em Sat, Aug 29, 2015 at 03:16:52AM +0000, He Kuang escreveu:
> > This patch implements arch_get_reg_info() for arm64 to enable
> > HAVE_BPF_PROLOGUE feature. For arm64, structure pt_regs is not composed
> > by fields of register names but an array of regs, so here we simply
> > multiply fixed register size by index number to get the byte offset.
>
> Hi Jean, Will, are you ok with this? Can I have Acked-by or Reviewed-by
> tags from you?

Any idea what this applies against? It's difficult to review it without
knowing what PERF_HAVE_ARCH_GET_REG_INFO or HAVE_BPF_PROLOGUE are.

Anyway, a couple of small comments below.

> He, please try to add the authors of the files you change in the CC
> list.
>
> - Arnaldo
>
> > Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
> > ---
> > tools/perf/arch/arm64/Makefile | 1 +
> > tools/perf/arch/arm64/util/dwarf-regs.c | 26 ++++++++++++++++++++++++++
> > 2 files changed, 27 insertions(+)

Any plan to do arch/arm/ too?

> > diff --git a/tools/perf/arch/arm64/Makefile b/tools/perf/arch/arm64/Makefile
> > index 7fbca17..1256e6e 100644
> > --- a/tools/perf/arch/arm64/Makefile
> > +++ b/tools/perf/arch/arm64/Makefile
> > @@ -1,3 +1,4 @@
> > ifndef NO_DWARF
> > PERF_HAVE_DWARF_REGS := 1
> > endif
> > +PERF_HAVE_ARCH_GET_REG_INFO := 1
> > diff --git a/tools/perf/arch/arm64/util/dwarf-regs.c b/tools/perf/arch/arm64/util/dwarf-regs.c
> > index d49efeb..cb2c50a 100644
> > --- a/tools/perf/arch/arm64/util/dwarf-regs.c
> > +++ b/tools/perf/arch/arm64/util/dwarf-regs.c
> > @@ -10,6 +10,10 @@
> >
> > #include <stddef.h>
> > #include <dwarf-regs.h>
> > +#include <string.h>
> > +#include <linux/ptrace.h>
> > +
> > +#define PT_REG_SIZE (sizeof(((struct user_pt_regs *)0)->regs[0]))

Why not add an "offset" field to pt_regs_dwarfnum and just calculate
that using offsetof in the GPR_DWARFNUM_NAME macro?

> >
> > struct pt_regs_dwarfnum {
> > const char *name;
> > @@ -78,3 +82,25 @@ const char *get_arch_regstr(unsigned int n)
> > return roff->name;
> > return NULL;
> > }
> > +
> > +#ifdef HAVE_BPF_PROLOGUE
> > +int arch_get_reg_info(const char *name, int *offset)
> > +{
> > + const struct pt_regs_dwarfnum *roff;
> > +
> > + if (!name || !offset)
> > + return -1;
> > +
> > + for (roff = regdwarfnum_table; roff->name != NULL; roff++) {
> > + if (!strcmp(roff->name, name)) {
> > + if (roff->dwarfnum < 0)

When is this ever true? Do we need up update REG_DWARFNUM_END to use
a negative index?

Will
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