[RFC PATCH v8 45/49] perf tools: Introduce arch_get_reg_info() for x86

[Wang Nan]

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.

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>
---
 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 cfbccc4..d6eeee8 100644
--- a/tools/perf/arch/x86/util/Build
+++ b/tools/perf/arch/x86/util/Build
@@ -2,6 +2,8 @@ libperf-y += header.o
 libperf-y += tsc.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..3cd2303 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
-- 
1.8.3.4

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