Re: [PATCH 23/31] perf tools: Introduce arch_get_reg_info() for x86
From: Wangnan (F)
Date: Mon Aug 31 2015 - 22:40:07 EST
On 2015/9/1 4:43, Arnaldo Carvalho de Melo wrote:
Em Sat, Aug 29, 2015 at 04:21:57AM +0000, Wang Nan escreveu:
From: He Kuang <hekuang@xxxxxxxxxx>
arch_get_reg_info() 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.
Is this something like:
/* Query offset/name of register from its name/offset */
extern int regs_query_register_offset(const char *name);
in ptrace? Can't we reuse that name and even code?
Unfortunately we can't reuse its code, because pt_regs is defined
differently
in user and kernel side.
In arch/x86/kernel/ptrace.c we have:
struct pt_regs_offset {
const char *name;
int offset;
};
#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct
pt_regs, r)}
#define REG_OFFSET_END {.name = NULL, .offset = 0}
static const struct pt_regs_offset regoffset_table[] = {
#ifdef CONFIG_X86_64
...
REG_OFFSET_NAME(r15),
REG_OFFSET_NAME(r14),
REG_OFFSET_NAME(r13),
...
The definition of REG_OFFSET_NAME relys on the field name and the string
name of a
register are identical. This is true for kernel, but not true for userspace.
For example, for x86_64, 'struct pt_regs' is defined in
arch/x86/include/asm/ptrace.h
for kernel, and the reigster name is 'ax, cx, dx, si, di ...'. In
contract, which is
defined in arch/x86/include/uapi/asm/ptrace.h for user, and the register
name becomes
'rax, rcx, rdx, rsi, rdi ...'.
Since logical of regs_query_register_offset() is very simple, changing
REG_OFFSET_NAME()
makes it a totally different function.
But yes, let's reuse its name. And it may worth considering to reuse its
code for other
archs.
Thank you.
Was this that was done and only a rename was made?
- Arnaldo
This patch replaces original string table by a 'struct reg_info' table,
which records offset of registers according to its name.
For x86, since there are two sub-archs (x86_32 and x86_64) but we can
only get pt_regs for the arch we are currently on, this patch fills
offset with '-1' for another sub-arch. This introduces a limitation to
perf prologue that, we are unable to generate prologue on a x86_32
compiled perf for BPF programs targeted on x86_64 kernel. This
limitation is acceptable, because this is a very rare usecase.
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>
Link: http://lkml.kernel.org/n/1436445342-1402-34-git-send-email-wangnan0@xxxxxxxxxx
---
tools/perf/arch/x86/Makefile | 1 +
tools/perf/arch/x86/util/Build | 2 +
tools/perf/arch/x86/util/dwarf-regs.c | 104 ++++++++++++++++++++++++----------
3 files changed, 78 insertions(+), 29 deletions(-)
diff --git a/tools/perf/arch/x86/Makefile b/tools/perf/arch/x86/Makefile
index 21322e0..a84a6f6f 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_GET_REG_INFO := 1
diff --git a/tools/perf/arch/x86/util/Build b/tools/perf/arch/x86/util/Build
index 2c55e1b..09429f6 100644
--- a/tools/perf/arch/x86/util/Build
+++ b/tools/perf/arch/x86/util/Build
@@ -3,6 +3,8 @@ libperf-y += tsc.o
libperf-y += pmu.o
libperf-y += kvm-stat.o
+# BPF_PROLOGUE also need dwarf-regs.o. However, if CONFIG_BPF_PROLOGUE
+# is true, CONFIG_DWARF must true.
libperf-$(CONFIG_DWARF) += dwarf-regs.o
libperf-$(CONFIG_LIBUNWIND) += unwind-libunwind.o
diff --git a/tools/perf/arch/x86/util/dwarf-regs.c b/tools/perf/arch/x86/util/dwarf-regs.c
index be22dd4..9928caf 100644
--- a/tools/perf/arch/x86/util/dwarf-regs.c
+++ b/tools/perf/arch/x86/util/dwarf-regs.c
@@ -22,44 +22,67 @@
#include <stddef.h>
#include <dwarf-regs.h>
+#include <string.h>
+#include <linux/ptrace.h>
+#include <linux/kernel.h> /* for offsetof */
+#include <util/bpf-loader.h>
+
+struct reg_info {
+ const char *name; /* Reg string in debuginfo */
+ int offset; /* Reg offset in struct pt_regs */
+};
/*
* Generic dwarf analysis helpers
*/
-
+/*
+ * x86_64 compiling can't access pt_regs for x86_32, so fill offset
+ * with -1.
+ */
+#ifdef __x86_64__
+# define REG_INFO(n, f) { .name = n, .offset = -1, }
+#else
+# define REG_INFO(n, f) { .name = n, .offset = offsetof(struct pt_regs, f), }
+#endif
#define X86_32_MAX_REGS 8
-const char *x86_32_regs_table[X86_32_MAX_REGS] = {
- "%ax",
- "%cx",
- "%dx",
- "%bx",
- "$stack", /* Stack address instead of %sp */
- "%bp",
- "%si",
- "%di",
+
+struct reg_info x86_32_regs_table[X86_32_MAX_REGS] = {
+ REG_INFO("%ax", eax),
+ REG_INFO("%cx", ecx),
+ REG_INFO("%dx", edx),
+ REG_INFO("%bx", ebx),
+ REG_INFO("$stack", esp), /* Stack address instead of %sp */
+ REG_INFO("%bp", ebp),
+ REG_INFO("%si", esi),
+ REG_INFO("%di", edi),
};
+#undef REG_INFO
+#ifdef __x86_64__
+# define REG_INFO(n, f) { .name = n, .offset = offsetof(struct pt_regs, f), }
+#else
+# define REG_INFO(n, f) { .name = n, .offset = -1, }
+#endif
#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",
+struct reg_info x86_64_regs_table[X86_64_MAX_REGS] = {
+ REG_INFO("%ax", rax),
+ REG_INFO("%dx", rdx),
+ REG_INFO("%cx", rcx),
+ REG_INFO("%bx", rbx),
+ REG_INFO("%si", rsi),
+ REG_INFO("%di", rdi),
+ REG_INFO("%bp", rbp),
+ REG_INFO("%sp", rsp),
+ REG_INFO("%r8", r8),
+ REG_INFO("%r9", r9),
+ REG_INFO("%r10", r10),
+ REG_INFO("%r11", r11),
+ REG_INFO("%r12", r12),
+ REG_INFO("%r13", r13),
+ REG_INFO("%r14", r14),
+ REG_INFO("%r15", r15),
};
-/* 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
@@ -71,5 +94,28 @@ const char *x86_64_regs_table[X86_64_MAX_REGS] = {
/* 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) ? arch_regs_table[n].name : NULL;
}
+
+#ifdef HAVE_BPF_PROLOGUE
+int arch_get_reg_info(const char *name, int *offset)
+{
+ int i;
+ struct reg_info *info;
+
+ if (!name || !offset)
+ return -1;
+
+ for (i = 0; i < ARCH_MAX_REGS; i++) {
+ info = &arch_regs_table[i];
+ if (strcmp(info->name, name) == 0) {
+ if (info->offset < 0)
+ return -1;
+ *offset = info->offset;
+ return 0;
+ }
+ }
+
+ return -1;
+}
+#endif
--
2.1.0
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