libubacktrace: Provide uClibc with backtrace functions

A new shared object, libubacktrace.so.0 is added to uClibc
to provide backtrace functions to support application self-debugging.
This set of functions requires to dynamically load libgcc_s.so so they
need to call dlopen/dlsym that are provided by libdl. For this reason
they cannot be included into libc.so.0 but are provided by a new library.

User application that wants to use backtrace needs to be compiled with
-fexceptions option and -rdynamic to get full symbols printed and must be
linked against libubacktrace.so

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

Makefile.in

@@ -48,6 +48,7 @@ include $(top_srcdir)libresolv/Makefile.in
 include $(top_srcdir)libutil/Makefile.in
 include $(top_srcdir)libpthread/Makefile.in
 include $(top_srcdir)librt/Makefile.in
+include $(top_srcdir)libubacktrace/Makefile.in
 include $(top_srcdir)extra/locale/Makefile.in
 
 # last included to catch all the objects added by others (locales/threads)
@@ -272,6 +273,7 @@ HEADERS_RM-$(UCLIBC_HAS_GLIBC_CUSTOM_PRINTF) += printf.h
 HEADERS_RM-$(UCLIBC_HAS_GLOB)                += glob.h
 HEADERS_RM-$(UCLIBC_HAS_GNU_ERROR)           += error.h
 HEADERS_RM-$(UCLIBC_HAS_IPV6)                += netinet/ip6.h netinet/icmp6.h
+HEADERS_RM-$(UCLIBC_HAS_BACKTRACE)           += execinfo.h
 HEADERS_RM-$(UCLIBC_HAS_LOCALE)              += iconv.h
 HEADERS_RM-$(UCLIBC_HAS_PTY)                 += pty.h
 HEADERS_RM-$(UCLIBC_HAS_REGEX)               += regex.h regexp.h
@@ -330,6 +332,12 @@ ifeq ($(HARDWIRED_ABSPATH),y)
 else
 	-$(INSTALL) -m 755 $(top_builddir)lib/libc.so $(PREFIX)$(DEVEL_PREFIX)$(MULTILIB_DIR)/
 endif
+ifeq ($(UCLIBC_HAS_BACKTRACE),y)
+# Add the AS_NEEDED entry for libubacktrace.so
+	if [ -f $(top_builddir)lib/libc.so -a -f $(PREFIX)$(RUNTIME_PREFIX)lib/$(SHARED_MAJORNAME) ] ; then \
+		echo "GROUP ( $(UBACKTRACE_ASNEEDED) )" >> $(PREFIX)$(DEVEL_PREFIX)lib/libc.so; \
+	fi
+endif
 ifeq ($(UCLIBC_HAS_THREADS),y)
 ifneq ($(LINUXTHREADS_OLD),y)
 ifeq ($(HARDWIRED_ABSPATH),y)

Makerules

@@ -32,12 +32,12 @@ shared_objs = $(libc-y:.o=.os) $(libc-shared-y) $(libc-nonshared-y) \
 	$(libpthread-so-y) $(libpthread-nonshared-y) $(libthread_db-so-y) \
 	$(libresolv-so-y) $(librt-so-y) \
 	$(ldso-y) \
-	$(libutil-so-y)
+	$(libutil-so-y) $(libubacktrace-so-y)
 
 ar_objs =  $(libc-y) $(libc-static-y) $(libcrypt-a-y) \
 	$(libdl-a-y) $(libintl-a-y) $(libm-a-y) $(libnsl-a-y) \
 	$(libpthread-a-y) $(libthread_db-a-y) \
-	$(libresolv-a-y) $(librt-a-y) $(libutil-a-y)
+	$(libresolv-a-y) $(librt-a-y) $(libutil-a-y) $(libubacktrace-a-y)
 ifeq ($(DOPIC),y)
 ar_objs := $(ar_objs:.o=.os)
 endif
@@ -455,7 +455,8 @@ files.dep := $(libc-a-y) $(libc-so-y) $(libc-nonshared-y) \
 	$(libthread_db-a-y) $(libthread_db-so-y) $(libpthread-generated-y) \
 	$(librt-a-y) $(librt-so-y)  $(libresolv-a-y) $(libresolv-so-y) \
 	$(libcrypt-a-y) $(libcrypt-so-y) $(libutil-a-y) $(libutil-so-y) \
-	$(libnsl-a-y) $(libnsl-so-y) $(ldso-y) $(libdl-a-y) $(libdl-so-y)
+	$(libnsl-a-y) $(libnsl-so-y) $(ldso-y) $(libdl-a-y) $(libdl-so-y) \
+	$(libubacktrace-a-y) $(libubacktrace-so-y)
 .depends.dep := \
 	$(patsubst %.s,%.s.dep,$(filter %.s,$(files.dep))) \
 	$(patsubst %.o,%.o.dep,$(filter %.o,$(files.dep))) \

Rules.mak

@@ -118,7 +118,7 @@ export MAJOR_VERSION MINOR_VERSION SUBLEVEL VERSION ABI_VERSION LC_ALL
 
 LIBC := libc
 SHARED_LIBNAME := $(LIBC).so.$(ABI_VERSION)
-
+UBACKTRACE_DSO := libubacktrace.so.$(MAJOR_VERSION)
 ifneq ($(findstring  $(TARGET_ARCH) , hppa64 ia64 mips64 powerpc64 s390x sparc64 x86_64 ),)
 UCLIBC_LDSO_NAME := ld64-uClibc
 ARCH_NATIVE_BIT := 64
@@ -528,6 +528,13 @@ link.asneeded = $(if $(and $(CC_FLAG_ASNEEDED),$(CC_FLAG_NO_ASNEEDED)),$(CC_FLAG
 # Check for AS_NEEDED support in linker script (binutils>=2.16.1 has it)
 ifndef ASNEEDED
 export ASNEEDED:=$(shell $(LD) --help 2>/dev/null | grep -q -- --as-needed && echo "AS_NEEDED ( $(UCLIBC_LDSO) )" || echo "$(UCLIBC_LDSO)")
+ifeq ($(UCLIBC_HAS_BACKTRACE),y)
+# Only used in installed libc.so linker script
+UBACKTRACE_FULL_NAME := $(RUNTIME_PREFIX)lib/$(UBACKTRACE_DSO)
+export UBACKTRACE_ASNEEDED:=$(shell $(LD) --help 2>/dev/null | grep -q -- --as-needed && echo "AS_NEEDED ( $(UBACKTRACE_FULL_NAME) )" || echo "$(UBACKTRACE_FULL_NAME)")
+else
+export UBACKTRACE_ASNEEDED:=""
+endif
 endif
 
 # Add a bunch of extra pedantic annoyingly strict checks

extra/Configs/Config.in

@@ -2308,6 +2308,25 @@ config UCLIBC_MALLOC_DEBUGGING
 	  Because this increases the size of malloc appreciably (due to strings
 	  etc), you should say N unless you need to debug a malloc problem.
 
+config UCLIBC_HAS_BACKTRACE
+	bool "Add support for application self-debugging"
+	depends on HAVE_SHARED && TARGET_sh
+	default n
+	help
+	  Answer Y here to compile support for application self-debugging, by adding
+	  a new shared object "libubacktrace.so" that provides the following new
+	  functions:
+	  backtrace, backtrace_symbols, backtrace_symbols_fd
+
+	  The backtrace functionality is currently supported on SH platform, and it
+	  based on dwarf2 informations to properly work, so any application that
+	  want to use backtrace needs to be built with -fexceptions flag.
+
+	  The symbol names may be unavailable without the use of special linker
+	  options. For systems using the GNU linker, it is necessary to use the
+	  -rdynamic linker option too. Note that names of "static" functions are not
+	  exposed, and won't be available in the backtrace.
+
 config WARNINGS
 	string "Compiler Warnings"
 	default "-Wall"

include/execinfo.h

@@ -0,0 +1,44 @@
+/* Copyright (C) 1998, 1999, 2004, 2005 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#ifndef _EXECINFO_H
+#define _EXECINFO_H 1
+
+#include <features.h>
+
+__BEGIN_DECLS
+
+/* Store up to SIZE return address of the current program state in
+   ARRAY and return the exact number of values stored.  */
+extern int backtrace (void **__array, int __size) __nonnull ((1));
+
+
+/* Return names of functions from the backtrace list in ARRAY in a newly
+   malloc()ed memory block.  */
+extern char **backtrace_symbols (void *__const *__array, int __size)
+     __THROW __nonnull ((1));
+
+
+/* This function is similar to backtrace_symbols() but it writes the result
+   immediately to a file.  */
+extern void backtrace_symbols_fd (void *__const *__array, int __size, int __fd)
+     __THROW __nonnull ((1));
+
+__END_DECLS
+
+#endif /* execinfo.h  */

libubacktrace/Makefile

@@ -0,0 +1,14 @@
+# Makefile for uClibc (libubacktrace)
+#
+# Copyright (C) 2010 STMicroelectronics Ltd
+# Author(s): Carmelo Amoroso <carmelo.amoroso@st.com>
+#
+# Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+#
+
+top_srcdir=../
+top_builddir=../
+include $(top_builddir)Rules.mak
+all: libs
+include Makefile.in
+include $(top_srcdir)Makerules

libubacktrace/Makefile.in

@@ -0,0 +1,84 @@
+# Makefile for uClibc (libubacktrace)
+#
+# Copyright (C) 2010 STMicroelectronics Ltd
+# Author: Carmelo Amoroso <carmelo.amoroso@st.com>
+
+# Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+#
+
+subdirs += libubacktrace
+
+CFLAGS-libubacktrace := -DNOT_IN_libc -DIS_IN_libubacktrace $(SSP_ALL_CFLAGS)
+
+LDFLAGS-libubacktrace.so := $(LDFLAGS) $(top_builddir)lib/libdl-$(VERSION).so
+
+LIBS-libubacktrace.so := $(LIBS)
+
+libubacktrace_FULL_NAME := libubacktrace-$(VERSION).so
+
+libubacktrace_DIR := $(top_srcdir)libubacktrace
+libubacktrace_OUT := $(top_builddir)libubacktrace
+libubacktrace_ARCH_DIR := $(libubacktrace_DIR)/sysdeps/$(TARGET_ARCH)
+libubacktrace_ARCH_OUT := $(libubacktrace_OUT)/sysdeps/$(TARGET_ARCH)
+
+-include $(libubacktrace_ARCH_DIR)/Makefile.arch
+
+libubacktrace_SRC-y :=
+libubacktrace_SRC-$(UCLIBC_HAS_BACKTRACE) := backtrace.c backtracesyms.c backtracesymsfd.c
+
+CFLAGS-libubacktrace/sysdeps/$(TARGET_ARCH)/ := $(CFLAGS-libubacktrace)
+
+# remove generic sources, if arch specific version is present
+ifneq ($(strip $(libubacktrace_ARCH_SRC-y)),)
+libubacktrace_SRC-y := $(filter-out $(notdir $(libubacktrace_ARCH_SRC-y)),$(libubacktrace_SRC-y))
+libubacktrace_ARCH_SRC := $(addprefix $(libubacktrace_ARCH_DIR)/,$(libubacktrace_ARCH_SRC-y))
+libubacktrace_ARCH_OBJ := $(patsubst $(libubacktrace_ARCH_DIR)/%.c,$(libubacktrace_ARCH_OUT)/%.o,$(libubacktrace_ARCH_SRC))
+endif
+
+
+libubacktrace_SRC := $(addprefix $(libubacktrace_DIR)/,$(libubacktrace_SRC-y))
+libubacktrace_OBJ := $(patsubst $(libubacktrace_DIR)/%.c,$(libubacktrace_OUT)/%.o,$(libubacktrace_SRC))
+
+libubacktrace_SRCS := $(libubacktrace_SRC) $(libubacktrace_ARCH_SRC)
+libubacktrace_OBJS := $(libubacktrace_OBJ) $(libubacktrace_ARCH_OBJ)
+
+ifeq ($(DOPIC),y)
+libubacktrace-a-y := $(libubacktrace_OBJS:.o=.os)
+else
+libubacktrace-a-y := $(libubacktrace_OBJS)
+endif
+libubacktrace-so-y := $(libubacktrace_OBJS:.o=.os)
+
+lib-a-$(UCLIBC_HAS_BACKTRACE) += $(top_builddir)lib/libubacktrace.a
+lib-so-$(UCLIBC_HAS_BACKTRACE) += $(top_builddir)lib/libubacktrace.so
+
+objclean-y += CLEAN_libubacktrace
+
+ifeq ($(DOMULTI),n)
+ifeq ($(DOPIC),y)
+$(top_builddir)lib/libubacktrace.so: $(top_builddir)lib/libubacktrace.a $(libdl.depend)
+else
+$(top_builddir)lib/libubacktrace.so: $(libubacktrace_OUT)/libubacktrace_so.a $(libdl.depend)
+endif
+	$(call link.so,$(libubacktrace_FULL_NAME),$(ABI_VERSION))
+else
+$(top_builddir)lib/libubacktrace.so: $(libubacktrace_OUT)/libubacktrace.oS | $(libdl.depend)
+	$(call linkm.so,$(libubacktrace_FULL_NAME),$(ABI_VERSION))
+endif
+
+$(libubacktrace_OUT)/libubacktrace_so.a: $(libubacktrace-so-y)
+	$(Q)$(RM) $@
+	$(do_ar)
+
+$(libubacktrace_OUT)/libubacktrace.oS: $(libubacktrace_SRCS)
+	$(Q)$(RM) $@
+	$(compile-m)
+
+$(top_builddir)lib/libubacktrace.a: $(libubacktrace-a-y)
+	$(Q)$(INSTALL) -d $(dir $@)
+	$(Q)$(RM) $@
+	$(do_ar)
+
+CLEAN_libubacktrace:
+	$(do_rm) $(addprefix $(libubacktrace_OUT)/*., o os oS a) \
+	 $(addprefix $(libubacktrace_ARCH_OUT)/*., o os oS a)

libubacktrace/backtrace.c

@@ -0,0 +1,19 @@
+/*
+ * Perform stack unwinding by using the _Unwind_Backtrace.
+ *
+ * User application that wants to use backtrace needs to be
+ * compiled with -fexceptions option and -rdynamic to get full
+ * symbols printed.
+
+ * Copyright (C) 2010 STMicroelectronics Ltd
+ * Author(s): Carmelo Amoroso <carmelo.amoroso@st.com>
+ *
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ *
+ */
+#error "Arch specific implementation must be provided to properly work"
+int backtrace (void **array, int size)
+{
+	return -1;
+}
+

libubacktrace/backtracesyms.c

@@ -0,0 +1,105 @@
+/* Return list with names for address in backtrace.
+   Copyright (C) 1998,1999,2000,2001,2003 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.
+
+   Based on glibc/sysdeps/generic/elf/backtracesyms.c
+
+   Copyright (C) 2010 STMicroelectronics Ltd
+   Author(s): Carmelo Amoroso <carmelo.amoroso@st.com>
+   * Modified to work with uClibc
+     - updated headers inclusion
+     - updated formatting and style
+     - updated to use dladdr from libdl */
+
+#include <execinfo.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <dlfcn.h>
+#include <link.h>	/* required for __ELF_NATIVE_CLASS */
+
+#if __ELF_NATIVE_CLASS == 32
+# define WORD_WIDTH 8
+#else
+/* We assyme 64bits.  */
+# define WORD_WIDTH 16
+#endif
+
+
+char ** backtrace_symbols (void *const *array,  int size)
+{
+	Dl_info info[size];
+	int status[size];
+	int cnt;
+	size_t total = 0;
+	char **result;
+
+	/* Fill in the information we can get from `dladdr'.  */
+	for (cnt = 0; cnt < size; ++cnt) {
+		status[cnt] = dladdr (array[cnt], &info[cnt]);
+		if (status[cnt] && info[cnt].dli_fname &&
+			info[cnt].dli_fname[0] != '\0')
+		/*
+		 * We have some info, compute the length of the string which will be
+		 * "<file-name>(<sym-name>) [+offset].
+		 */
+		total += (strlen (info[cnt].dli_fname ?: "") +
+				  (info[cnt].dli_sname ?
+				  strlen (info[cnt].dli_sname) + 3 + WORD_WIDTH + 3 : 1)
+				  + WORD_WIDTH + 5);
+		else
+			total += 5 + WORD_WIDTH;
+	}
+
+	/* Allocate memory for the result.  */
+	result = (char **) malloc (size * sizeof (char *) + total);
+	if (result != NULL) {
+		char *last = (char *) (result + size);
+		for (cnt = 0; cnt < size; ++cnt) {
+			result[cnt] = last;
+
+			if (status[cnt] && info[cnt].dli_fname
+				&& info[cnt].dli_fname[0] != '\0') {
+
+				char buf[20];
+
+				if (array[cnt] >= (void *) info[cnt].dli_saddr)
+					sprintf (buf, "+%#lx",
+							(unsigned long)(array[cnt] - info[cnt].dli_saddr));
+				else
+					sprintf (buf, "-%#lx",
+					(unsigned long)(info[cnt].dli_saddr - array[cnt]));
+
+				last += 1 + sprintf (last, "%s%s%s%s%s[%p]",
+				info[cnt].dli_fname ?: "",
+				info[cnt].dli_sname ? "(" : "",
+				info[cnt].dli_sname ?: "",
+				info[cnt].dli_sname ? buf : "",
+				info[cnt].dli_sname ? ") " : " ",
+				array[cnt]);
+			} else
+				last += 1 + sprintf (last, "[%p]", array[cnt]);
+		}
+		assert (last <= (char *) result + size * sizeof (char *) + total);
+	}
+
+	return result;
+}

libubacktrace/backtracesymsfd.c

@@ -0,0 +1,116 @@
+/* Write formatted list with names for addresses in backtrace to a file.
+   Copyright (C) 1998, 2000, 2003, 2005 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.
+
+   Based on glibc/sysdeps/generic/elf/backtracesymsfd.c
+
+   Copyright (C) 2010 STMicroelectronics Ltd
+   Author(s): Carmelo Amoroso <carmelo.amoroso@st.com>
+   * Modified to work with uClibc
+     - updated headers inclusion
+     - updated formatting and style
+     - updated to use dladdr from libdl
+     - updated to use snprintf instead of _itoa_word */
+
+#include <execinfo.h>
+#include <string.h>
+#include <sys/uio.h>
+#include <dlfcn.h>
+#include <stdio.h>
+#include <link.h>	/* required for __ELF_NATIVE_CLASS */
+
+#if __ELF_NATIVE_CLASS == 32
+# define WORD_WIDTH 8
+#else
+/* We assyme 64bits.  */
+# define WORD_WIDTH 16
+#endif
+
+#define BUF_SIZE (WORD_WIDTH + 1)
+
+void backtrace_symbols_fd (void *const *array, int size, int fd)
+{
+	struct iovec iov[9];
+	int cnt;
+
+	for (cnt = 0; cnt < size; ++cnt) {
+		char buf[BUF_SIZE];
+		Dl_info info;
+		size_t last = 0;
+		size_t len = 0;
+
+		memset(buf, 0, sizeof(buf));
+		if (dladdr (array[cnt], &info)
+			&& info.dli_fname && info.dli_fname[0] != '\0')	{
+			/* Name of the file.  */
+			iov[0].iov_base = (void *) info.dli_fname;
+			iov[0].iov_len = strlen (info.dli_fname);
+			last = 1;
+
+			/* Symbol name.  */
+			if (info.dli_sname != NULL) {
+				char buf2[BUF_SIZE];
+				memset(buf2, 0, sizeof(buf2));
+				size_t diff;
+
+				iov[1].iov_base = (void *) "(";
+				iov[1].iov_len = 1;
+				iov[2].iov_base = (void *) info.dli_sname;
+				iov[2].iov_len = strlen (info.dli_sname);
+
+				if (array[cnt] >= (void *) info.dli_saddr) {
+					iov[3].iov_base = (void *) "+0x";
+					diff = array[cnt] - info.dli_saddr;
+				} else {
+					iov[3].iov_base = (void *) "-0x";
+					diff = info.dli_saddr - array[cnt];
+				}
+
+				iov[3].iov_len = 3;
+
+				/* convert diff to a string in hex format */
+				len = snprintf(buf2, sizeof(buf2), "%lx", (unsigned long) diff);
+				iov[4].iov_base = buf2;
+				iov[4].iov_len = len;
+
+				iov[5].iov_base = (void *) ")";
+				iov[5].iov_len = 1;
+
+				last = 6;
+			}
+		}
+
+		iov[last].iov_base = (void *) "[0x";
+		iov[last].iov_len = 3;
+		++last;
+
+		/* convert array[cnt] to a string in hex format */
+		len = snprintf(buf, sizeof(buf), "%lx", (unsigned long) array[cnt]);
+		iov[last].iov_base = buf;
+		iov[last].iov_len = len;
+
+		++last;
+
+		iov[last].iov_base = (void *) "]\n";
+		iov[last].iov_len = 2;
+		++last;
+
+		writev (fd, iov, last);
+	}
+}

libubacktrace/sysdeps/sh/Makefile.arch

@@ -0,0 +1,12 @@
+# Makefile for uClibc (sh/libubacktrace)
+#
+# Copyright (C) 2010 STMicroelectronics Ltd
+# Author: Carmelo Amoroso <carmelo.amoroso@st.com>
+
+# Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+#
+
+libubacktrace_ARCH_SRC-y := backtrace.c
+
+# -fexections is required for backtrace to work using dwarf2
+CFLAGS-backtrace.c := -fexceptions

libubacktrace/sysdeps/sh/backtrace.c

@@ -0,0 +1,84 @@
+/*
+ * Perform stack unwinding by using the _Unwind_Backtrace.
+ *
+ * User application that wants to use backtrace needs to be
+ * compiled with -fexceptions option and -rdynamic to get full
+ * symbols printed.
+ *
+ * Copyright (C) 2009, 2010 STMicroelectronics Ltd.
+ *
+ * Author(s): Giuseppe Cavallaro <peppe.cavallaro@st.com>
+ * - Initial implementation for glibc
+ *
+ * Author(s): Carmelo Amoroso <carmelo.amoroso@st.com>
+ * - Reworked for uClibc
+ *   - use dlsym/dlopen from libdl
+ *   - rewrite initialisation to not use libc_once
+ *   - make it available in static link too
+ *
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ *
+ */
+
+#include <execinfo.h>
+#include <dlfcn.h>
+#include <stdlib.h>
+#include <unwind.h>
+#include <assert.h>
+#include <stdio.h>
+
+struct trace_arg
+{
+  void **array;
+  int cnt, size;
+};
+
+static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
+static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
+
+static void backtrace_init (void)
+{
+	void *handle = dlopen ("libgcc_s.so.1", RTLD_LAZY);
+
+	if (handle == NULL
+		|| ((unwind_backtrace = dlsym (handle, "_Unwind_Backtrace")) == NULL)
+		|| ((unwind_getip = dlsym (handle, "_Unwind_GetIP")) == NULL)) {
+		printf("libgcc_s.so.1 must be installed for backtrace to work\n");
+		abort();
+	}
+}
+
+static _Unwind_Reason_Code
+backtrace_helper (struct _Unwind_Context *ctx, void *a)
+{
+	struct trace_arg *arg = a;
+
+	assert (unwind_getip != NULL);
+
+	/* We are first called with address in the __backtrace function. Skip it. */
+	if (arg->cnt != -1)
+		arg->array[arg->cnt] = (void *) unwind_getip (ctx);
+	if (++arg->cnt == arg->size)
+		return _URC_END_OF_STACK;
+	return _URC_NO_REASON;
+}
+
+/*
+ * Perform stack unwinding by using the _Unwind_Backtrace.
+ *
+ * User application that wants to use backtrace needs to be
+ * compiled with -fexceptions option and -rdynamic to get full
+ * symbols printed.
+ */
+int backtrace (void **array, int size)
+{
+	struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
+
+	if (unwind_backtrace == NULL)
+		backtrace_init();
+
+	if (size >= 1)
+		unwind_backtrace (backtrace_helper, &arg);
+
+	return arg.cnt != -1 ? arg.cnt : 0;
+}