Date:	Tue, 1 Sep 2015 11:14:14 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
Cc:	"'Wang Nan'" <wangnan0@...wei.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
	Kaixu Xia <xiakaixu@...wei.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Zefan Li <lizefan@...wei.com>,
	"pi3orama@....com" <pi3orama@....com>
Subject: Re: [PATCH 23/31] perf tools: Introduce regs_query_register_offset()
 for x86

Em Tue, Sep 01, 2015 at 11:47:41AM +0000, 平松雅巳 / HIRAMATU，MASAMI escreveu:
> > From: Wang Nan [mailto:wangnan0@...wei.com]
> > 
> > regs_query_register_offset() is a helper function which converts
> > register name like "%rax" to offset of a register in 'struct pt_regs',
> > which is required by BPF prologue generator. Since the function is
> > identical, try to reuse the code in arch/x86/kernel/ptrace.c.
> > 
> > Comment inside dwarf-regs.c list the differences between this
> > implementation and kernel code.
> 
> Hmm, this also introduce a duplication of the code...
> It might be a good time to move them into arch/x86/lib/ and
> reuse it directly from perf code.

It is strange to, having tried sharing stuff directly from the kernel,
to be now in a position where I advocate against it...

Copy'n'pasting what I said in another message:

-----
We would go back to sharing stuff with the kernel, but this time around
we would be using something that everybody knows is being shared, which
doesn't elliminates the possibility that at some point changes made with
the kernel in mind would break the tools/ using code.

Perhaps it is better to keep copying what we want and introduce
infrastructure to check for differences and warn us as soon as possible
so that we would do the copy, test if it doesn't break what we use, etc.

I.e. we wouldn't be putting any new burden on the "kernel people", i.e.
the burden of having to check that changes they make don't break tools/
living code, nor any out of the blue breakage on tools/ for tools/
developers to fix when changes are made on the kernel "side" -----
---

The "stop sharing directly stuff with the kernel" stance was taken after
a report from Linus about breakage due to tools/ using kernel files
directly and then a change made in some RCU files broke the tools/perf/
build, even with tools/perf/ not using anything RCU related so far.

Looking at tools/perf/MANIFEST, the file used to create a detached
tarball so that perf can be built outside the kernel sources there are
still some kernel source files listed, but those probably need to be
copied too...

- Arnaldo
 
> Thank you,
> 
> > 
> > get_arch_regstr() switches to regoffset_table and the old string table
> > is dropped.
> > 
> > Signed-off-by: Wang Nan <wangnan0@...wei.com>
> > Signed-off-by: He Kuang <hekuang@...wei.com>
> > Cc: Alexei Starovoitov <ast@...mgrid.com>
> > Cc: Brendan Gregg <brendan.d.gregg@...il.com>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Cc: David Ahern <dsahern@...il.com>
> > Cc: He Kuang <hekuang@...wei.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Kaixu Xia <xiakaixu@...wei.com>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Paul Mackerras <paulus@...ba.org>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Cc: Zefan Li <lizefan@...wei.com>
> > Cc: pi3orama@....com
> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> >  tools/perf/arch/x86/Makefile          |   1 +
> >  tools/perf/arch/x86/util/Build        |   1 +
> >  tools/perf/arch/x86/util/dwarf-regs.c | 122 ++++++++++++++++++++++++----------
> >  3 files changed, 90 insertions(+), 34 deletions(-)
> > 
> > diff --git a/tools/perf/arch/x86/Makefile b/tools/perf/arch/x86/Makefile
> > index 21322e0..09ba923 100644
> > --- a/tools/perf/arch/x86/Makefile
> > +++ b/tools/perf/arch/x86/Makefile
> > @@ -2,3 +2,4 @@ ifndef NO_DWARF
> >  PERF_HAVE_DWARF_REGS := 1
> >  endif
> >  HAVE_KVM_STAT_SUPPORT := 1
> > +PERF_HAVE_ARCH_REGS_QUERY_REGISTER_OFFSET := 1
> > diff --git a/tools/perf/arch/x86/util/Build b/tools/perf/arch/x86/util/Build
> > index 2c55e1b..d4d1f23 100644
> > --- a/tools/perf/arch/x86/util/Build
> > +++ b/tools/perf/arch/x86/util/Build
> > @@ -4,6 +4,7 @@ libperf-y += pmu.o
> >  libperf-y += kvm-stat.o
> > 
> >  libperf-$(CONFIG_DWARF) += dwarf-regs.o
> > +libperf-$(CONFIG_BPF_PROLOGUE) += dwarf-regs.o
> > 
> >  libperf-$(CONFIG_LIBUNWIND)          += unwind-libunwind.o
> >  libperf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> > diff --git a/tools/perf/arch/x86/util/dwarf-regs.c b/tools/perf/arch/x86/util/dwarf-regs.c
> > index a08de0a..de5b936 100644
> > --- a/tools/perf/arch/x86/util/dwarf-regs.c
> > +++ b/tools/perf/arch/x86/util/dwarf-regs.c
> > @@ -21,55 +21,109 @@
> >   */
> > 
> >  #include <stddef.h>
> > +#include <errno.h> /* for EINVAL */
> > +#include <string.h> /* for strcmp */
> > +#include <linux/ptrace.h> /* for struct pt_regs */
> > +#include <linux/kernel.h> /* for offsetof */
> >  #include <dwarf-regs.h>
> > 
> >  /*
> > - * Generic dwarf analysis helpers
> > + * See arch/x86/kernel/ptrace.c.
> > + * Different from it:
> > + *
> > + *  - Since struct pt_regs is defined differently for user and kernel,
> > + *    but we want to use 'ax, bx' instead of 'rax, rbx' (which is struct
> > + *    field name of user's pt_regs), we make REG_OFFSET_NAME to accept
> > + *    both string name and reg field name.
> > + *
> > + *  - Since accessing x86_32's pt_regs from x86_64 building is difficult
> > + *    and vise versa, we simply fill offset with -1, so
> > + *    get_arch_regstr() still works but regs_query_register_offset()
> > + *    returns error.
> > + *    The only inconvenience caused by it now is that we are not allowed
> > + *    to generate BPF prologue for a x86_64 kernel if perf is built for
> > + *    x86_32. This is really a rare usecase.
> > + *
> > + *  - Order is different from kernel's ptrace.c for get_arch_regstr(), which
> > + *    is defined by dwarf.
> >   */
> > 
> > -#define X86_32_MAX_REGS 8
> > -const char *x86_32_regs_table[X86_32_MAX_REGS] = {
> > -	"%ax",
> > -	"%cx",
> > -	"%dx",
> > -	"%bx",
> > -	"$stack",	/* Stack address instead of %sp */
> > -	"%bp",
> > -	"%si",
> > -	"%di",
> > +struct pt_regs_offset {
> > +	const char *name;
> > +	int offset;
> > +};
> > +
> > +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> > +
> > +#ifdef __x86_64__
> > +# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
> > +# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = -1}
> > +#else
> > +# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = -1}
> > +# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
> > +#endif
> > +
> > +static const struct pt_regs_offset x86_32_regoffset_table[] = {
> > +	REG_OFFSET_NAME_32("%ax",	eax),
> > +	REG_OFFSET_NAME_32("%cx",	ecx),
> > +	REG_OFFSET_NAME_32("%dx",	edx),
> > +	REG_OFFSET_NAME_32("%bx",	ebx),
> > +	REG_OFFSET_NAME_32("$stack",	esp),	/* Stack address instead of %sp */
> > +	REG_OFFSET_NAME_32("%bp",	ebp),
> > +	REG_OFFSET_NAME_32("%si",	esi),
> > +	REG_OFFSET_NAME_32("%di",	edi),
> > +	REG_OFFSET_END,
> >  };
> > 
> > -#define X86_64_MAX_REGS 16
> > -const char *x86_64_regs_table[X86_64_MAX_REGS] = {
> > -	"%ax",
> > -	"%dx",
> > -	"%cx",
> > -	"%bx",
> > -	"%si",
> > -	"%di",
> > -	"%bp",
> > -	"%sp",
> > -	"%r8",
> > -	"%r9",
> > -	"%r10",
> > -	"%r11",
> > -	"%r12",
> > -	"%r13",
> > -	"%r14",
> > -	"%r15",
> > +static const struct pt_regs_offset x86_64_regoffset_table[] = {
> > +	REG_OFFSET_NAME_64("%ax",	rax),
> > +	REG_OFFSET_NAME_64("%dx",	rdx),
> > +	REG_OFFSET_NAME_64("%cx",	rcx),
> > +	REG_OFFSET_NAME_64("%bx",	rbx),
> > +	REG_OFFSET_NAME_64("%si",	rsi),
> > +	REG_OFFSET_NAME_64("%di",	rdi),
> > +	REG_OFFSET_NAME_64("%bp",	rbp),
> > +	REG_OFFSET_NAME_64("%sp",	rsp),
> > +	REG_OFFSET_NAME_64("%r8",	r8),
> > +	REG_OFFSET_NAME_64("%r9",	r9),
> > +	REG_OFFSET_NAME_64("%r10",	r10),
> > +	REG_OFFSET_NAME_64("%r11",	r11),
> > +	REG_OFFSET_NAME_64("%r12",	r12),
> > +	REG_OFFSET_NAME_64("%r13",	r13),
> > +	REG_OFFSET_NAME_64("%r14",	r14),
> > +	REG_OFFSET_NAME_64("%r15",	r15),
> > +	REG_OFFSET_END,
> >  };
> > 
> >  /* TODO: switching by dwarf address size */
> >  #ifdef __x86_64__
> > -#define ARCH_MAX_REGS X86_64_MAX_REGS
> > -#define arch_regs_table x86_64_regs_table
> > +#define regoffset_table x86_64_regoffset_table
> >  #else
> > -#define ARCH_MAX_REGS X86_32_MAX_REGS
> > -#define arch_regs_table x86_32_regs_table
> > +#define regoffset_table x86_32_regoffset_table
> >  #endif
> > 
> > +/* Minus 1 for the ending REG_OFFSET_END */
> > +#define ARCH_MAX_REGS ((sizeof(regoffset_table) / sizeof(regoffset_table[0])) - 1)
> > +
> >  /* Return architecture dependent register string (for kprobe-tracer) */
> >  const char *get_arch_regstr(unsigned int n)
> >  {
> > -	return (n < ARCH_MAX_REGS) ? arch_regs_table[n] : NULL;
> > +	return (n < ARCH_MAX_REGS) ? regoffset_table[n].name : NULL;
> > +}
> > +
> > +/* Reuse code from arch/x86/kernel/ptrace.c */
> > +/**
> > + * regs_query_register_offset() - query register offset from its name
> > + * @name:	the name of a register
> > + *
> > + * regs_query_register_offset() returns the offset of a register in struct
> > + * pt_regs from its name. If the name is invalid, this returns -EINVAL;
> > + */
> > +int regs_query_register_offset(const char *name)
> > +{
> > +	const struct pt_regs_offset *roff;
> > +	for (roff = regoffset_table; roff->name != NULL; roff++)
> > +		if (!strcmp(roff->name, name))
> > +			return roff->offset;
> > +	return -EINVAL;
> >  }
> > --
> > 1.8.3.4
> 
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