[PATCH 19/27] perf tools: Introduce regs_query_register_offset() for x86

From: Wang Nan
Date: Sun Sep 06 2015 - 03:15:37 EST

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.

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>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
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: 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/1441090789-108382-2-git-send-email-wangnan0@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 ff63649..4659703 100644
--- a/tools/perf/arch/x86/util/Build
+++ b/tools/perf/arch/x86/util/Build
@@ -5,6 +5,7 @@ libperf-y += kvm-stat.o
libperf-y += perf_regs.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..9223c16 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(). Use
+ * the order 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;
}
--
2.1.0

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