RE: [PATCH 23/31] perf tools: Introduce regs_query_register_offset() for x86

[åæéå / HIRAMATUïMASAMI]

> From: Arnaldo Carvalho de Melo [mailto:acme@xxxxxxxxxx]
> 
> Em Tue, Sep 01, 2015 at 11:47:41AM +0000, åæéå / HIRAMATUïMASAMI escreveu:
> > > From: Wang Nan [mailto:wangnan0@xxxxxxxxxx]
> > >
> > > 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...

OK, so let this apply.

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>

And also we'll need a testcase for this.

Thank you,

> 
> - Arnaldo
> 
> > Thank you,
> >
> > >
> > > get_arch_regstr() switches to regoffset_table and the old string table
> > > is dropped.
> > >
> > > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> > > Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
> > > Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> > > Cc: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
> > > Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> > > Cc: David Ahern <dsahern@xxxxxxxxx>
> > > Cc: He Kuang <hekuang@xxxxxxxxxx>
> > > Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> > > Cc: Kaixu Xia <xiakaixu@xxxxxxxxxx>
> > > Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> > > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > > Cc: Paul Mackerras <paulus@xxxxxxxxx>
> > > Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > Cc: Zefan Li <lizefan@xxxxxxxxxx>
> > > Cc: pi3orama@xxxxxxx
> > > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> > > ---
> > >  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
> >