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

["Wangnan (F)" <wangnan0@huawei.com>]

On 2015/9/1 23:54, 平松雅巳 / HIRAMATU，MASAMI wrote:
>> From: Arnaldo Carvalho de Melo [mailto:acme@redhat.com]
>>
>> Em Tue, Sep 01, 2015 at 11:47:41AM +0000, 平松雅巳 / HIRAMATU，MASAMI escreveu:
>>>> From: Wang Nan [mailto:wangnan0@huawei.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...
> OK, so let this apply.
>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>
> And also we'll need a testcase for this.

I created a testcase for the whole BPF prologue, so I think this can be 
covered?

I'll post them by replying this mail.

Thank you.

> 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@huawei.com>
>>>> Signed-off-by: He Kuang <hekuang@huawei.com>
>>>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>>>> Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
>>>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>>>> Cc: David Ahern <dsahern@gmail.com>
>>>> Cc: He Kuang <hekuang@huawei.com>
>>>> Cc: Jiri Olsa <jolsa@kernel.org>
>>>> Cc: Kaixu Xia <xiakaixu@huawei.com>
>>>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>>>> Cc: Namhyung Kim <namhyung@kernel.org>
>>>> Cc: Paul Mackerras <paulus@samba.org>
>>>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>>> Cc: Zefan Li <lizefan@huawei.com>
>>>> Cc: pi3orama@163.com
>>>> Cc: Arnaldo Carvalho de Melo <acme@redhat.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