perf tools: Introduce regs_query_register_offset() for x86

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: He Kuang <hekuang@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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: 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
Link: http://lkml.kernel.org/r/1441523623-152703-20-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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

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;
 }