[RFC PATCH 11/11] perf: Support for dwarf cfi unwinding on post processing

[Frederic Weisbecker]

This brings the support for dwarf cfi unwinding on perf
post processing. Call frame informations are retrieved and
then passed to libunwind that requests memory and register content
from the applications. We use the stack and regs dumped with
samples to retrieve the context state necessary for this unwinding.

No specific options are needed for perf report to handle this,
just run it as usual.

Only x86-32 is supported for now.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Tom Zanussi <tzanussi@xxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Robert Richter <robert.richter@xxxxxxx>
Cc: Frank Ch. Eigler <fche@xxxxxxxxxx>
---
 tools/perf/Makefile         |    1 +
 tools/perf/builtin-report.c |    9 +-
 tools/perf/util/callchain.c |   35 ++-
 tools/perf/util/callchain.h |   19 +-
 tools/perf/util/unwind.c    | 1112 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 1169 insertions(+), 7 deletions(-)
 create mode 100644 tools/perf/util/unwind.c

diff --git a/tools/perf/Makefile b/tools/perf/Makefile
index 0c46ac7..601c69a 100644
--- a/tools/perf/Makefile
+++ b/tools/perf/Makefile
@@ -468,6 +468,7 @@ LIB_OBJS += $(OUTPUT)util/hist.o
 LIB_OBJS += $(OUTPUT)util/probe-event.o
 LIB_OBJS += $(OUTPUT)util/util.o
 LIB_OBJS += $(OUTPUT)util/cpumap.o
+LIB_OBJS += $(OUTPUT)util/unwind.o
 
 BUILTIN_OBJS += $(OUTPUT)builtin-annotate.o
 
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 5de405d..b48e218 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -30,6 +30,8 @@
 #include "util/sort.h"
 #include "util/hist.h"
 
+#include <linux/err.h>
+
 static char		const *input_name = "perf.data";
 
 static bool		force, use_tui, use_stdio;
@@ -87,6 +89,7 @@ static int perf_session__add_hist_entry(struct perf_session *self,
 	struct hist_entry *he;
 	struct hists *hists;
 	struct perf_event_attr *attr;
+	struct dwarf_callchain *dc;
 
 	if ((sort__has_parent || symbol_conf.use_callchain) && data->callchain) {
 		syms = perf_session__resolve_callchain(self, al->thread,
@@ -95,6 +98,10 @@ static int perf_session__add_hist_entry(struct perf_session *self,
 			return -ENOMEM;
 	}
 
+	dc = callchain_unwind(self, al->thread, data);
+	if (IS_ERR(dc))
+		return PTR_ERR(dc);
+
 	attr = perf_header__find_attr(data->id, &self->header);
 	if (attr)
 		hists = perf_session__hists_findnew(self, data->id, attr->type, attr->config);
@@ -108,7 +115,7 @@ static int perf_session__add_hist_entry(struct perf_session *self,
 	err = 0;
 	if (symbol_conf.use_callchain) {
 		err = callchain_append(he->callchain, data->callchain, syms,
-				       data->period);
+				       dc, data->period);
 		if (err)
 			goto out_free_syms;
 	}
diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index e12d539..54ca387 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -365,8 +365,10 @@ append_chain(struct callchain_node *root, struct resolved_chain *chain,
 }
 
 static void filter_context(struct ip_callchain *old, struct resolved_chain *new,
-			   struct map_symbol *syms)
+			   struct map_symbol *syms,
+			   struct dwarf_callchain *dwarf_chain)
 {
+	struct dwarf_callchain_entry *entry, *tmp;
 	int i, j = 0;
 
 	for (i = 0; i < (int)old->nr; i++) {
@@ -379,23 +381,46 @@ static void filter_context(struct ip_callchain *old, struct resolved_chain *new,
 	}
 
 	new->nr = j;
+
+	if (!dwarf_chain)
+		return;
+
+	list_for_each_entry_safe(entry, tmp, &dwarf_chain->chain_head, list) {
+		new->ips[j].ip = entry->ip;
+		new->ips[j].ms = entry->ms;
+		j++;
+
+		list_del(&entry->list);
+		free(entry);
+	}
+
+	new->nr += dwarf_chain->nb;
+
+	free(dwarf_chain);
 }
 
 
 int callchain_append(struct callchain_root *root, struct ip_callchain *chain,
-		     struct map_symbol *syms, u64 period)
+		     struct map_symbol *syms,
+		     struct dwarf_callchain *dwarf_chain, u64 period)
 {
 	struct resolved_chain *filtered;
+	int entries;
+
+	entries = chain->nr;
+
+	if (dwarf_chain)
+		entries += dwarf_chain->nb;
 
-	if (!chain->nr)
+	if (!entries)
 		return 0;
 
 	filtered = zalloc(sizeof(*filtered) +
-			  chain->nr * sizeof(struct resolved_ip));
+			  entries * sizeof(struct resolved_ip));
 	if (!filtered)
 		return -ENOMEM;
 
-	filter_context(chain, filtered, syms);
+	filter_context(chain, filtered, syms, dwarf_chain);
 
 	if (!filtered->nr)
 		goto end;
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index c15fb8c..9fb55b4 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -31,6 +31,17 @@ struct callchain_root {
 	struct callchain_node	node;
 };
 
+struct dwarf_callchain_entry {
+	struct list_head	list;
+	u64			ip;
+	struct map_symbol	ms;
+};
+
+struct dwarf_callchain {
+	int			nb;
+	struct list_head	chain_head;
+};
+
 struct callchain_param;
 
 typedef void (*sort_chain_func_t)(struct rb_root *, struct callchain_root *,
@@ -68,8 +79,14 @@ static inline u64 cumul_hits(struct callchain_node *node)
 
 int register_callchain_param(struct callchain_param *param);
 int callchain_append(struct callchain_root *root, struct ip_callchain *chain,
-		     struct map_symbol *syms, u64 period);
+		     struct map_symbol *syms,
+		     struct dwarf_callchain *dwarf_chain, u64 period);
+
 int callchain_merge(struct callchain_root *dst, struct callchain_root *src);
 
 bool ip_callchain__valid(struct ip_callchain *chain, const event_t *event);
+
+struct dwarf_callchain *callchain_unwind(struct perf_session *session,
+					 struct thread *thread,
+					 struct sample_data *data);
 #endif	/* __PERF_CALLCHAIN_H */
diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
new file mode 100644
index 0000000..b8dc23f
--- /dev/null
+++ b/tools/perf/util/unwind.c
@@ -0,0 +1,1112 @@
+/*
+ * Post mortem Dwarf CFI based unwinding on top of regs and stack dumps.
+ *
+ * Lots of this code have been borrowed or heavily inspired from parts of
+ * the libunwind 0.99 code which are (amongst other contributors I may have
+ * forgotten):
+ *
+ * Copyright (C) 2002-2007 Hewlett-Packard Co
+ *	Contributed by David Mosberger-Tang <davidm@xxxxxxxxxx>
+ *
+ * And the bugs have been added by:
+ *
+ * Copyright (C) 2010, Frederic Weisbecker <fweisbec@xxxxxxxxx>
+ *
+ */
+
+#include "util.h"
+#include <elf.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <linux/list.h>
+#include <linux/err.h>
+#include "thread.h"
+#include "session.h"
+#include "perf_regs.h"
+
+
+#ifdef LIBUNWIND_SUPPORT
+
+#include <libunwind-ptrace.h>
+#include <libunwind.h>
+
+struct pt_regs {
+	unsigned long ebx;
+	unsigned long ecx;
+	unsigned long edx;
+	unsigned long esi;
+	unsigned long edi;
+	unsigned long ebp;
+	unsigned long eax;
+	unsigned long ds;
+	unsigned long es;
+	unsigned long fs;
+	unsigned long gs;
+	unsigned long orig_ax;
+	unsigned long eip;
+	unsigned long cs;
+	unsigned long flags;
+	unsigned long esp;
+	unsigned long ss;
+};
+
+#define DW_EH_PE_FORMAT_MASK	0x0f	/* format of the encoded value */
+#define DW_EH_PE_APPL_MASK	0x70	/* how the value is to be applied */
+/*
+ * Flag bit.  If set, the resulting pointer is the address of the word
+ * that contains the final address.
+ */
+#define DW_EH_PE_indirect	0x80
+
+/* Pointer-encoding formats: */
+#define DW_EH_PE_omit		0xff
+#define DW_EH_PE_ptr		0x00	/* pointer-sized unsigned value */
+#define DW_EH_PE_uleb128	0x01	/* unsigned LE base-128 value */
+#define DW_EH_PE_udata2		0x02	/* unsigned 16-bit value */
+#define DW_EH_PE_udata4		0x03	/* unsigned 32-bit value */
+#define DW_EH_PE_udata8		0x04	/* unsigned 64-bit value */
+#define DW_EH_PE_sleb128	0x09	/* signed LE base-128 value */
+#define DW_EH_PE_sdata2		0x0a	/* signed 16-bit value */
+#define DW_EH_PE_sdata4		0x0b	/* signed 32-bit value */
+#define DW_EH_PE_sdata8		0x0c	/* signed 64-bit value */
+
+/* Pointer-encoding application: */
+#define DW_EH_PE_absptr		0x00	/* absolute value */
+#define DW_EH_PE_pcrel		0x10	/* rel. to addr. of encoded value */
+#define DW_EH_PE_textrel	0x20	/* text-relative (GCC-specific???) */
+#define DW_EH_PE_datarel	0x30	/* data-relative */
+/*
+ * The following are not documented by LSB v1.3, yet they are used by
+ * GCC, presumably they aren't documented by LSB since they aren't
+ * used on Linux:
+ */
+#define DW_EH_PE_funcrel	0x40	/* start-of-procedure-relative */
+#define DW_EH_PE_aligned	0x50	/* aligned pointer */
+
+struct dwarf_instr_addr {
+	u64			start;
+	u64			end;
+	struct dso		*dso;
+	struct list_head	list;
+};
+
+struct unwind_info {
+	struct sample_data	*sample;
+	struct perf_session	*session;
+	struct thread		*thread;
+	struct list_head	dia_head;
+};
+
+static int
+resolve_section_name(int fd, Elf32_Ehdr *ehdr, int idx, char *buf, int size)
+{
+	Elf32_Shdr shdr;
+	int offset;
+	int old;
+	int i;
+	char c;
+
+	old = lseek(fd, 0, SEEK_CUR);
+	offset = ehdr->e_shoff + (ehdr->e_shstrndx * ehdr->e_shentsize);
+	lseek(fd, offset, SEEK_SET);
+	if (read(fd, &shdr, ehdr->e_shentsize) == -1)
+		return -errno;
+
+	offset = shdr.sh_offset + idx;
+	lseek(fd, offset, SEEK_SET);
+
+	for (i = 0; i < size - 1; i++) {
+		if (read(fd, &c, 1) == -1)
+			return -errno;
+		if (!c)
+			break;
+		buf[i] = c;
+	}
+
+	buf[i] = 0;
+	lseek(fd, old, SEEK_SET);
+
+	return 0;
+}
+
+
+static int eh_frame_section(int fd, Elf32_Ehdr *ehdr, Elf32_Shdr *shdr)
+{
+	int i, err;
+
+	lseek(fd, ehdr->e_shoff + ehdr->e_shentsize, SEEK_SET);
+
+	for (i = 1; i < ehdr->e_shnum; i++) {
+		char buf[128];
+
+		if (read(fd, shdr, ehdr->e_shentsize) == -1)
+			return -errno;
+
+		err = resolve_section_name(fd, ehdr, shdr->sh_name, buf, sizeof(buf));
+		if (err)
+			return err;
+
+		if (!strcmp(buf, ".eh_frame"))
+			return 0;
+	}
+
+	return -ENOENT;
+}
+
+static int parse_elf_headers(int fd, Elf32_Ehdr *ehdr)
+{
+	if (read(fd, ehdr, sizeof(*ehdr)) == -1)
+		return -errno;
+
+	if (ehdr->e_ident[EI_MAG0] != ELFMAG0 ||
+		ehdr->e_ident[EI_MAG1] != ELFMAG1 ||
+		ehdr->e_ident[EI_MAG2] != ELFMAG2 ||
+		ehdr->e_ident[EI_MAG3] != ELFMAG3) {
+
+		return -EINVAL;
+	}
+
+	if (!ehdr->e_shoff)
+		return -ENOENT;
+
+	return 0;
+}
+
+static u64 dwarf_read_uleb128(int fd, u64 *val)
+{
+	u64 shift = 0;
+	unsigned char byte;
+
+	*val = 0;
+
+	do {
+		if (read(fd, &byte, sizeof(byte)) == -1)
+			return -errno;
+
+		*val |= (byte & 0x7f) << shift;
+		shift += 7;
+	} while (byte & 0x80);
+
+	return 0;
+}
+
+static s64 dwarf_read_sleb128(int fd, s64 *val)
+{
+	s64 shift = 0;
+	unsigned char byte;
+
+	*val = 0;
+
+	do {
+		if (read(fd, &byte, sizeof(byte)) == -1)
+			return -errno;
+		*val |= (byte & 0x7f) << shift;
+		shift += 7;
+	} while (byte & 0x80);
+
+	if (shift < 8 * sizeof(*val) && (byte & 0x40) != 0)
+		/* sign-extend negative value */
+		*val |= -1LL << shift;
+
+	return 0;
+}
+
+static int dwarf_read_encoded_pointer(int fd, unsigned char encoding,
+				      u64 drop __used, u64 *val)
+{
+	u64 base = lseek(fd, 0, SEEK_CUR);
+
+	if (encoding == DW_EH_PE_omit || encoding == DW_EH_PE_aligned) {
+		pr_err("Unsupported dwarf encoding\n");
+		return -ENOSYS;
+	}
+
+	switch (encoding & DW_EH_PE_FORMAT_MASK) {
+	case DW_EH_PE_ptr: {
+		unsigned long lval;
+
+		if (read(fd, &lval, sizeof(lval)) == -1)
+			return -errno;
+		*val = lval;
+		break;
+	}
+	case DW_EH_PE_sdata4: {
+		s32 s32val;
+		s64 s64val;
+
+		if (read(fd, &s32val, sizeof(s32val)) == -1)
+			return -errno;
+		s64val = s32val;
+		*val = *(u64 *)&s64val;
+		break;
+	}
+	default:
+		pr_err("Unsupported encoded pointer: %d\n", encoding & DW_EH_PE_FORMAT_MASK);
+		return -EINVAL;
+	}
+
+	switch (encoding & DW_EH_PE_APPL_MASK) {
+	case DW_EH_PE_absptr:
+		break;
+	case DW_EH_PE_pcrel:
+		*val += base;
+		break;
+	default:
+		pr_err("Unsupported DW_EH_PE_APPL_MASK: %d\n", encoding & DW_EH_PE_APPL_MASK);
+		return -EINVAL;
+	}
+
+	if (encoding & DW_EH_PE_indirect) {
+		int prev_offset = lseek(fd, 0, SEEK_CUR);
+		unsigned long lval;
+
+		lseek(fd, *val, SEEK_SET);
+		if (read(fd, &lval, sizeof(unsigned long)) == -1)
+			return -errno;
+		*val = lval;
+		lseek(fd, prev_offset, SEEK_SET);
+	}
+
+	return 0;
+}
+
+struct cie {
+	u32		length;
+	u64		ext_length;
+	union {
+			u32 id32;
+			u64 id64;
+	};
+	u8		version;
+	u64		code_align;
+	s64		data_align;
+	u8		ret_column;
+	u64		aug_length;
+	u8		lsda_encoding;
+	u8		fde_encoding; /* Should have defaults */
+	u8		handler_encoding;
+	u8		have_abi_marker;
+	u64		handler;
+	u64		instr;
+	u64		end;
+};
+
+static int parse_cie(int fd, struct cie *cie)
+{
+	char aug_str[10];
+	int size, end, base;
+	int err;
+	int i;
+
+	memset(cie, 0, sizeof(*cie));
+
+	if (read(fd, &cie->length, sizeof(cie->length)) == -1)
+		return -errno;
+
+	if (cie->length == 0xffffffff) {
+		if (read(fd, &cie->ext_length, sizeof(cie->ext_length)) == -1)
+			return -errno;
+
+		size = cie->ext_length;
+		base = lseek(fd, 0, SEEK_CUR);
+		if (read(fd, &cie->id64, sizeof(cie->id64)) == -1)
+			return -errno;
+
+		if (cie->id64)
+			return -EINVAL;
+	} else {
+		base = lseek(fd, 0, SEEK_CUR);
+		if (read(fd, &cie->id32, sizeof(cie->id32)) == -1)
+			return -errno;
+		size = cie->length;
+		if (cie->id32)
+			return -EINVAL;
+	}
+	end = base + size;
+
+	if (read(fd, &cie->version, sizeof(cie->version)) == -1)
+		return -errno;
+
+	/* Should be else in 64 bits? */
+	if (cie->version != 1)
+		return -EINVAL;
+
+	memset(aug_str, 0, sizeof(aug_str));
+	for (i = 0; i < (int)sizeof(aug_str); i++) {
+		char c;
+
+		if (read(fd, &c, 1) == -1)
+			return -errno;
+
+		aug_str[i] = c;
+		if (!c)
+			break;
+	}
+
+	if (!strcmp("eh", aug_str))
+		lseek(fd, 4, SEEK_CUR);
+
+	err = dwarf_read_uleb128(fd, &cie->code_align);
+	if (err)
+		return err;
+
+	err = dwarf_read_sleb128(fd, &cie->data_align);
+	if (err)
+		return err;
+
+
+	if (read(fd, &cie->ret_column, sizeof(cie->ret_column)) == -1)
+		return -errno;
+
+	if (aug_str[0] == 'z') {
+		err = dwarf_read_uleb128(fd, &cie->aug_length);
+		if (err)
+			return err;
+	}
+
+
+	for (i = 1; aug_str[i]; i++) {
+		switch (aug_str[i]) {
+		case 'L':
+			if (read(fd, &cie->lsda_encoding, sizeof(cie->lsda_encoding)) == -1)
+				return -errno;
+			break;
+		case 'R':
+			if (read(fd, &cie->fde_encoding, sizeof(cie->fde_encoding)) == -1)
+				return -errno;
+			break;
+		case 'P':
+			if (read(fd, &cie->handler_encoding, sizeof(cie->handler_encoding)) == -1)
+				return -errno;
+
+			err = dwarf_read_encoded_pointer(fd, cie->handler_encoding, 0,
+								&cie->handler);
+			if (err)
+				return err;
+			break;
+		case 'S':
+			if (read(fd, &cie->have_abi_marker, sizeof(cie->have_abi_marker)) == -1)
+				return -errno;
+			break;
+		default:
+			break;
+		}
+	}
+	cie->instr = lseek(fd, 0, SEEK_CUR);
+	cie->end = end;
+
+	return 0;
+}
+
+struct fde {
+	u32	length;
+	u64	ext_length;
+	union {
+		u32	cie_offset32;
+		u64	cie_offset64;
+	};
+	u64	pc_begin;
+	u64	pc_range;
+	u64	aug_length;
+	u64	aug_end;
+	u64	lsda;
+	u16	abi;
+	u16	tag;
+	u64	end;
+};
+
+static int parse_fde(int fd, struct fde *fde, struct cie *cie, int fde_end)
+{
+	int ip_range_encoding;
+	int err;
+
+	memset(fde, 0, sizeof(*fde));
+	ip_range_encoding = cie->fde_encoding & DW_EH_PE_FORMAT_MASK;
+
+	err = dwarf_read_encoded_pointer(fd, cie->fde_encoding, 0, &fde->pc_begin);
+	if (err)
+		return err;
+	err = dwarf_read_encoded_pointer(fd, ip_range_encoding, 0, &fde->pc_range);
+	if (err)
+		return err;
+	fde->pc_range += fde->pc_begin;
+
+	if (cie->aug_length) {
+		err = dwarf_read_uleb128(fd, &fde->aug_length);
+		if (err)
+			return err;
+		fde->aug_end = lseek(fd, 0, SEEK_CUR) + fde->aug_length;
+	}
+
+	err = dwarf_read_encoded_pointer(fd, cie->lsda_encoding, 0, &fde->lsda);
+	if (err)
+		return err;
+
+	if (cie->have_abi_marker) {
+		if (read(fd, &fde->abi, sizeof(fde->abi)) == -1)
+			return -EINVAL;
+		if (read(fd, &fde->tag, sizeof(fde->tag)) == -1)
+			return -EINVAL;
+	}
+
+	if (!cie->aug_length)
+		fde->aug_end = lseek(fd, 0, SEEK_CUR);
+	fde->end = fde_end;
+
+	return 0;
+}
+
+struct dwarf_cie_info {
+	unw_word_t cie_instr_start;	/* start addr. of CIE "initial_instructions" */
+	unw_word_t cie_instr_end;	/* end addr. of CIE "initial_instructions" */
+	unw_word_t fde_instr_start;	/* start addr. of FDE "instructions" */
+	unw_word_t fde_instr_end;	/* end addr. of FDE "instructions" */
+	unw_word_t code_align;		/* code-alignment factor */
+	unw_word_t data_align;		/* data-alignment factor */
+	unw_word_t ret_addr_column;	/* column of return-address register */
+	unw_word_t handler;		/* address of personality-routine */
+	uint16_t abi;
+	uint16_t tag;
+	uint8_t fde_encoding;
+	uint8_t lsda_encoding;
+	unsigned int sized_augmentation : 1;
+	unsigned int have_abi_marker : 1;
+};
+
+static int
+cfi_match_fill(unw_word_t addr, struct cie *cie, struct fde *fde,
+		unw_proc_info_t *pi, int need_unwind_info)
+{
+	struct dwarf_cie_info *dci;
+
+	if (addr < fde->pc_begin || addr >= fde->pc_range)
+		return -1;
+
+	pi->start_ip = fde->pc_begin;
+	pi->end_ip = fde->pc_range;
+	pi->lsda = fde->lsda;
+	pi->handler = cie->handler;
+	pi->format = UNW_INFO_FORMAT_TABLE;
+
+	if (!need_unwind_info)
+		return 0;
+
+	dci = calloc(1, sizeof(*dci));
+	if (!dci)
+		return -ENOMEM;
+
+	dci->cie_instr_start = cie->instr;
+	dci->cie_instr_end = cie->end;
+	dci->fde_instr_start = fde->aug_end;
+	dci->fde_instr_end = fde->end;
+	dci->code_align = cie->code_align;
+	dci->data_align = cie->data_align;
+	dci->ret_addr_column = cie->ret_column;
+	dci->handler = pi->handler;
+	dci->abi = fde->abi;
+	dci->tag = fde->tag;
+	dci->fde_encoding = cie->fde_encoding;
+	dci->lsda_encoding = cie->lsda_encoding;
+	dci->sized_augmentation = !!cie->aug_length;
+	dci->have_abi_marker = cie->have_abi_marker;
+	pi->unwind_info_size = sizeof(*dci);
+	pi->unwind_info = dci;
+
+	return 0;
+}
+
+static int get_cfi_info(int fd, unw_word_t addr, Elf32_Shdr *eh_shdr,
+			unw_proc_info_t *pi, int need_unwind_info)
+{
+	int start, end;
+
+	start = eh_shdr->sh_offset;
+	end = start + eh_shdr->sh_size;
+
+	lseek(fd, start, SEEK_SET);
+
+	/*
+	 * For now, do a slow linear search of the fde matching that address.
+	 * Support for binary search across .eh_frame_hdr will come after.
+	 */
+	for (;;) {
+		int base, val_offset;
+		struct cie cie;
+		struct fde fde;
+		u32 size32, val32;
+		s64 size, val;
+
+		base = lseek(fd, 0, SEEK_CUR);
+		if (base >= end)
+			break;
+
+		if (read(fd, &size32, sizeof(size32)) == -1)
+			return -EINVAL;
+
+		if (size32 == 0xffffffff) {
+			if (read(fd, &size, sizeof(size)) == -1)
+				return -EINVAL;
+			val_offset = lseek(fd, 0, SEEK_CUR);
+			if (read(fd, &val, sizeof(val)) == -1)
+				return -EINVAL;
+		} else {
+			val_offset = lseek(fd, 0, SEEK_CUR);
+			if (read(fd, &val32, sizeof(val32)) == -1)
+				return -EINVAL;
+			val = val32;
+			size = size32;
+		}
+
+		if (val) {
+			int offset, err;
+
+			offset = lseek(fd, 0, SEEK_CUR);
+			lseek(fd, val_offset - val, SEEK_SET);
+			if (parse_cie(fd, &cie)) {
+				pr_debug("Incorrect cie %llx %llx\n", val_offset - val, val);
+				break;
+			}
+
+			lseek(fd, offset, SEEK_SET);
+			if (parse_fde(fd, &fde, &cie, size + val_offset)) {
+				pr_debug("Incorrect fde\n");
+				break;
+			}
+
+			err = cfi_match_fill(addr, &cie, &fde, pi, need_unwind_info);
+			if (err != -1)
+				return err;
+			if (!err)
+				return 0;
+		}
+
+		lseek(fd, val_offset + size, SEEK_SET);
+	}
+
+	return -ENOENT;
+}
+
+static void find_address_location(unw_word_t ip, struct unwind_info *ui,
+				  struct addr_location *al)
+{
+	thread__find_addr_map(ui->thread, ui->session, PERF_RECORD_MISC_USER,
+			   MAP__FUNCTION, ui->thread->pid, ip, al);
+}
+
+static int track_dwarf_instr_addr(unw_proc_info_t *pi, struct unwind_info *ui,
+				  struct addr_location *al)
+{
+	struct dwarf_instr_addr *dia_cie, *dia_fde;
+	struct dwarf_cie_info *dci;
+
+	dia_cie = malloc(sizeof(*dia_cie));
+	if (!dia_cie)
+		return -ENOMEM;
+
+	dci = (struct dwarf_cie_info *)pi->unwind_info;
+
+	dia_cie->start = dci->cie_instr_start - 1;
+	dia_cie->end = dci->cie_instr_end;
+	dia_cie->dso = al->map->dso;
+
+	list_add_tail(&dia_cie->list, &ui->dia_head);
+
+	dia_fde = malloc(sizeof(*dia_fde));
+	if (!dia_fde) {
+		list_del(&dia_cie->list);
+		free(dia_cie);
+		return -ENOMEM;
+	}
+
+	dia_fde->start = dci->fde_instr_start - 1;
+	dia_fde->end = dci->fde_instr_end;
+	dia_fde->dso = al->map->dso;
+
+	list_add_tail(&dia_fde->list, &ui->dia_head);
+
+	return 0;
+}
+
+static int
+find_proc_info(unw_addr_space_t as __used, unw_word_t ip, unw_proc_info_t *pi,
+	      int need_unwind_info, void *arg)
+{
+	int err;
+	int fd;
+	unw_word_t addr;
+	char *path;
+	Elf32_Ehdr ehdr;
+	Elf32_Shdr eh_shdr;
+	struct addr_location al;
+	struct unwind_info *ui = arg;
+
+	find_address_location(ip, ui, &al);
+
+	if (!al.map || !al.map->dso)
+		return -EINVAL;
+
+	path = al.map->dso->long_name;
+	if (!path)
+		return -ENOENT;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0) {
+		close(fd);
+		return fd;
+	}
+
+	err = parse_elf_headers(fd, &ehdr);
+	if (err) {
+		close(fd);
+		return err;
+	}
+
+	err = eh_frame_section(fd, &ehdr, &eh_shdr);
+	if (err) {
+		close(fd);
+		return err;
+	}
+
+	if (ehdr.e_type == ET_DYN)
+		addr = al.map->map_ip(al.map, ip);
+	else
+		addr = ip;
+
+	err = get_cfi_info(fd, addr, &eh_shdr, pi, need_unwind_info);
+	if (err) {
+		close(fd);
+		return err;
+	}
+
+	if (need_unwind_info) {
+		err = track_dwarf_instr_addr(pi, ui, &al);
+		close(fd);
+		return err;
+	}
+
+	close(fd);
+
+	return 0;
+}
+
+static int access_fpreg(unw_addr_space_t __used as, unw_regnum_t __used num,
+			unw_fpreg_t __used *val, int __used __write,
+			void __used *arg)
+{
+	pr_warning("Unwind: fpreg unsupported yet\n");
+
+	return -1;
+}
+
+static int get_dyn_info_list_addr(unw_addr_space_t __used as,
+				  unw_word_t __used *dil_addr,
+				  void __used *arg)
+{
+	return -UNW_ENOINFO;
+}
+
+static int resume(unw_addr_space_t __used as, unw_cursor_t __used *cu,
+		  void __used *arg)
+{
+	pr_warning("Unwind: resume\n");
+
+	return 0;
+}
+
+static int
+get_proc_name(unw_addr_space_t __used as, unw_word_t __used addr,
+		char __used *bufp, size_t __used buf_len,
+		unw_word_t __used *offp, void __used *arg)
+{
+	*offp = 0;
+
+	return 0;
+}
+
+static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
+			  unw_word_t *valp)
+{
+	struct thread *thread = ui->thread;
+	struct perf_session *session = ui->session;
+	struct addr_location al;
+	int fd;
+	u64 offset;
+
+	thread__find_addr_map(thread, session, PERF_RECORD_MISC_USER,
+			   MAP__FUNCTION, thread->pid, addr, &al);
+	if (!al.map) {
+		pr_debug("unwind: not found map for %lx\n", (unsigned long)addr);
+		return -1;
+	}
+
+	offset = al.map->map_ip(al.map, addr);
+	fd = open(al.map->dso->long_name, O_RDONLY);
+	if (fd < 0) {
+		const char *name;
+
+		name = al.map ? al.map->dso->long_name : "Sais pas";
+		pr_debug("unwind: Can't open dso %s\n", name);
+
+		return -1;
+	}
+
+	if (lseek(fd, offset, SEEK_SET) == -1) {
+		close(fd);
+		pr_err("unwind: Can't seek\n");
+		return -1;
+	}
+	if (read(fd, valp, sizeof(*valp)) == -1) {
+		close(fd);
+		return -errno;
+	}
+	close(fd);
+
+	pr_debug("access mem offset: %llx va: %lx val: %lx\n",
+			offset, (unsigned long)addr, (unsigned long)*valp);
+
+	return 0;
+}
+
+static int access_dwarf_instr(struct unwind_info *ui, unw_word_t addr,
+			  unw_word_t *valp)
+{
+	struct dwarf_instr_addr *dia;
+	int found = 0;
+	int fd;
+
+	/*
+	 * This is quite crappy. There may be conflicts between dso adresses
+	 * here. Probably we only need to keep track of the last dso here.
+	 */
+	list_for_each_entry(dia, &ui->dia_head, list) {
+		if (addr >= dia->start && addr < dia->end) {
+			found = 1;
+			break;
+		}
+	}
+
+	if (!found)
+		return -ENOENT;
+
+	fd = open(dia->dso->long_name, O_RDONLY);
+	if (fd < 0)
+		return -EINVAL;
+
+	lseek(fd, addr, SEEK_SET);
+	if (read(fd, valp, sizeof(*valp)) == -1)
+		return -errno;
+
+	close(fd);
+
+	return 0;
+}
+
+static int reg_value(unw_word_t *valp, struct user_regs *regs, int id,
+		     u64 sample_regs)
+{
+	int i, idx = 0;
+
+	if (!(sample_regs & (1 << id)))
+		return -EINVAL;
+
+	for (i = 0; i < id; i++) {
+		if (sample_regs & (1 << i))
+			idx++;
+	}
+
+	*valp = regs->regs[idx];
+
+	return 0;
+}
+
+static int access_mem(unw_addr_space_t __used as,
+                      unw_word_t addr, unw_word_t *valp,
+                      int __write, void *arg)
+{
+	struct unwind_info *ui = arg;
+	struct user_stack_dump *stack = &ui->sample->stack;
+	unw_word_t start, end;
+	unw_word_t *val;
+	int offset;
+	int ret;
+
+	/* Don't support write, probably not needed */
+	if (__write || !stack || !ui->sample->uregs.version) {
+		*valp = 0;
+		return 0;
+	}
+
+	ret = reg_value(&start, &ui->sample->uregs, PERF_X86_32_REG_ESP,
+			ui->session->sample_uregs);
+	if (ret)
+		return ret;
+
+	end = start + stack->size;
+
+	ret = access_dwarf_instr(ui, addr, valp);
+	if (!ret)
+		return 0;
+
+	if (addr < start || addr + sizeof(unw_word_t) >= end) {
+		ret = access_dso_mem(ui, addr, valp);
+		if (ret) {
+			pr_debug("access_mem %p not inside range %p-%p\n",
+				(void *)addr, (void *)start, (void *)end);
+			*valp = 0;
+			return ret;
+		}
+		return 0;
+	}
+
+	offset = addr - start;
+	val = (void *)&stack->data[offset];
+	*valp = *val;
+
+	pr_debug("access_mem %p %lx\n", (void *)addr, (unsigned long)*valp);
+
+	return 0;
+}
+
+static int access_reg(unw_addr_space_t __used as,
+                      unw_regnum_t regnum, unw_word_t *valp,
+                      int __write, void *arg)
+{
+	struct unwind_info *ui = arg;
+	int id, ret;
+
+	/* Don't support write, I suspect we don't need it */
+	if (__write) {
+		pr_err("access_reg w %d\n", regnum);
+		return 0;
+	}
+
+	if (!ui->sample->uregs.version) {
+		*valp = 0;
+		return 0;
+	}
+
+	switch (regnum) {
+	case UNW_X86_EAX:
+		id = PERF_X86_32_REG_EAX;
+		break;
+	case UNW_X86_EDX:
+		id = PERF_X86_32_REG_EDX;
+		break;
+	case UNW_X86_ECX:
+		id = PERF_X86_32_REG_ECX;
+		break;
+	case UNW_X86_EBX:
+		id = PERF_X86_32_REG_EBX;
+		break;
+	case UNW_X86_ESI:
+		id = PERF_X86_32_REG_ESI;
+		break;
+	case UNW_X86_EDI:
+		id = PERF_X86_32_REG_EDI;
+		break;
+	case UNW_X86_EBP:
+		id = PERF_X86_32_REG_EBP;
+		break;
+	case UNW_X86_ESP:
+		id = PERF_X86_32_REG_ESP;
+		break;
+	case UNW_X86_EIP:
+		id = PERF_X86_32_REG_EIP;
+		break;
+	default:
+		pr_err("can't read reg %d\n", regnum);
+		return -EINVAL;
+	}
+
+	ret = reg_value(valp, &ui->sample->uregs, id, ui->session->sample_uregs);
+	if (ret) {
+		pr_err("can't read reg %d\n", regnum);
+		return ret;
+	}
+
+	pr_debug("reg: %d val: %lx\n", regnum, (unsigned long)*valp);
+
+	return 0;
+}
+
+static void put_unwind_info(unw_addr_space_t __used as, unw_proc_info_t *pi,
+			    void *arg)
+{
+	struct unwind_info *ui = arg;
+	struct dwarf_instr_addr *dia, *tmp;
+
+	if (pi->unwind_info) {
+		free(pi->unwind_info);
+		pi->unwind_info = NULL;
+	}
+
+	list_for_each_entry_safe(dia, tmp, &ui->dia_head, list) {
+		list_del(&dia->list);
+		free(dia);
+	}
+}
+
+static unw_accessors_t accessors = {
+	.find_proc_info		= find_proc_info,
+	.put_unwind_info	= put_unwind_info,
+	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
+	.access_mem		= access_mem,
+	.access_reg		= access_reg,
+	.access_fpreg		= access_fpreg,
+	.resume			= resume,
+	.get_proc_name		= get_proc_name,
+};
+
+static int
+append_dwarf_chain(struct dwarf_callchain *callchain,
+		   struct addr_location *al)
+{
+	struct dwarf_callchain_entry *entry;
+
+	entry = calloc(sizeof(*entry), 1);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->ip = al->addr;
+	entry->ms.map = al->map;
+	entry->ms.sym = al->sym;
+
+	list_add_tail(&entry->list, &callchain->chain_head);
+
+	callchain->nb++;
+
+	return 0;
+}
+
+
+static void callchain_unwind_release(struct dwarf_callchain *callchain)
+{
+	struct dwarf_callchain_entry *entry, *tmp;
+
+	list_for_each_entry_safe(entry, tmp, &callchain->chain_head, list) {
+		list_del(&entry->list);
+		free(entry);
+	}
+
+	free(callchain);
+}
+
+
+struct dwarf_callchain *callchain_unwind(struct perf_session *session,
+					 struct thread *thread,
+					 struct sample_data *data)
+{
+	struct dwarf_callchain *callchain;
+	unw_addr_space_t addr_space;
+	struct addr_location al;
+	struct unwind_info ui;
+	unw_cursor_t c;
+	unw_word_t ip;
+	int ret;
+
+	if (!data->uregs.version)
+		return NULL;
+
+	callchain = malloc(sizeof(*callchain));
+	if (!callchain)
+		return ERR_PTR(-ENOMEM);
+
+	callchain->nb = 0;
+	INIT_LIST_HEAD(&callchain->chain_head);
+
+	ret = reg_value(&ip, &data->uregs, PERF_X86_32_REG_EIP,
+			session->sample_uregs);
+	if (ret)
+		return ERR_PTR(ret);
+
+	thread__find_addr_location(thread, session,
+				   PERF_RECORD_MISC_USER,
+				   MAP__FUNCTION, thread->pid,
+				   ip, &al, NULL);
+
+	ret = append_dwarf_chain(callchain, &al);
+	if (ret)
+		goto fail;
+
+	memset(&ui, 0, sizeof(ui));
+	addr_space = unw_create_addr_space(&accessors, 0);
+	if (!addr_space) {
+		pr_err("Can't create unwind address space\n");
+		goto fail;
+	}
+
+	pr_debug("\n----- %s -----\n", al.map ? al.map->dso->long_name : "Unknown");
+	ui.sample = data;
+	ui.thread = thread;
+	ui.session = session;
+	INIT_LIST_HEAD(&ui.dia_head);
+
+	ret = unw_init_remote(&c, addr_space, &ui);
+	switch (ret) {
+	case UNW_EINVAL:
+		pr_err("Unwind: only supports local\n");
+		break;
+	case UNW_EUNSPEC:
+		pr_err("Unwind: unspecified error\n");
+		break;
+	case UNW_EBADREG:
+		pr_err("Unwind: register unavailable\n");
+		break;
+	default:
+		break;
+	}
+
+	if (ret)
+		goto fail_addrspace;
+
+	if (al.sym)
+		pr_debug("%s:ip = %llx\n", al.sym->name, al.addr);
+	else
+		pr_debug("ip = %llx\n", al.addr);
+
+	while (unw_step(&c) > 0) {
+		char name[250];
+		unsigned int offset;
+
+		unw_get_reg(&c, UNW_REG_IP, &ip);
+
+		thread__find_addr_location(thread, session,
+				   PERF_RECORD_MISC_USER,
+				   MAP__FUNCTION, thread->pid,
+				   ip, &al, NULL);
+
+		unw_get_proc_name(&c, name, sizeof(name), &offset);
+		if (al.sym)
+			pr_debug("%s:ip = %lx\n", al.sym->name, (unsigned long)ip);
+		else
+			pr_debug("ip = %lx (%llx)\n", (unsigned long)ip,
+					al.map ? al.map->map_ip(al.map, ip) : (u64)ip);
+
+		ret = append_dwarf_chain(callchain, &al);
+		if (ret)
+			goto fail_addrspace;
+	}
+
+	unw_destroy_addr_space(addr_space);
+
+	return callchain;
+
+fail_addrspace:
+	unw_destroy_addr_space(addr_space);
+fail:
+	callchain_unwind_release(callchain);
+	return ERR_PTR(ret);
+}
+
+#else /* LIBUNWIND_SUPPORT */
+
+struct dwarf_callchain *callchain_unwind(struct perf_session *session __used,
+					 struct thread *thread __used,
+					 struct sample_data *data __used)
+{
+	return NULL;
+}
+
+#endif
-- 
1.6.2.3

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