Re: [PATCHv4] print stack trace after each syscall

[Masatake Y. <ya...@re...>]

After rebuilding libunwind with enabling minidebuginfo feature[1], your
patch works fine on my Fedora 19.  

strace maintainer(s), is there any issue for merging the patch to 
the official source tree?

[1] https://bugzilla.redhat.com/show_bug.cgi?id=972737

Masatake YAMATO

> This patch prints the stack trace of the traced process after
> each system call when using -k flag. It uses libunwind to
> unwind the stack and to obtain the function name pointed by
> the IP.
> 
> Tested on Ubuntu 12.04 64 with the distribution version of
> libunwind (0.99-0.3ubuntu1) and on CentOS 6.3 with libunwind
> form the source code.
> 
> This code was originally taken from strace-plus of Philip J. Guo.
> 
>  v4:
>    updated man page
> 
>  v3:
>    adjusted several datatype to use unsigned (Denys)
>    fix sybol_name leak (Denys)
>    workaround for libunwind bug with libpthread (unw_step does
>         not return 1 when at the end of the stack)
>    fix several problem in in autoconf script (Dmitry)
>    use PATH_MAX for DSO file path buffer
> 
>  v2:
>    fixed several identation issues
>    removed a strlen in alloc_mmap_cache (Denys)
>    reload mmap_cache after execv
>    fixed a bug in libunwind_backtrace binary search (Masatake)
>    check return value of _UPT_create
>    use die_out_of_memory after Xalloc
>    use exiting instead of !entering
>    created a new separate unwind.c file
>    removed include from defs.h
>    added --with-libunwind to autoconf script
>    cleaned up defs.h from several inclusions
> ---
>  Makefile.am  |   10 ++-
>  configure.ac |   79 ++++++++++++++++++++
>  defs.h       |   42 +++++++++++
>  mem.c        |   15 ++++
>  process.c    |   14 ++++
>  strace.1     |    5 +-
>  strace.c     |   43 +++++++++++
>  syscall.c    |    9 +++
>  unwind.c     |  230 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  9 files changed, 445 insertions(+), 2 deletions(-)
>  create mode 100644 unwind.c
> 
> diff --git a/Makefile.am b/Makefile.am
> index 9d611f3..c8ad026 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -12,7 +12,7 @@ ARCH		= @arch@
>  
>  ACLOCAL_AMFLAGS = -I m4
>  AM_CFLAGS = $(WARN_CFLAGS)
> -AM_CPPFLAGS = -I$(srcdir)/$(OS)/$(ARCH) -I$(srcdir)/$(OS) -I$(builddir)/$(OS)
> +AM_CPPFLAGS = -I$(srcdir)/$(OS)/$(ARCH) -I$(srcdir)/$(OS) -I$(builddir)/$(OS) $(libunwind_CPPFLAGS)
>  
>  strace_SOURCES =	\
>  	bjm.c		\
> @@ -43,6 +43,14 @@ strace_SOURCES =	\
>  	util.c		\
>  	vsprintf.c
>  
> +
> +if LIB_UNWIND
> +strace_SOURCES += unwind.c
> +strace_LDADD = $(libunwind_LIBS)
> +AM_LDFLAGS = $(libunwind_LDFLAGS)
> +endif
> +
> +
>  noinst_HEADERS = defs.h
>  # Enable this to get link map generated
>  #strace_CFLAGS = $(AM_CFLAGS) -Wl,-Map=strace.mapfile
> diff --git a/configure.ac b/configure.ac
> index b3b62e8..0f64a12 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -265,6 +265,85 @@ AC_CHECK_MEMBERS([struct sigcontext.sc_hi2],,, [#include <signal.h>
>  # include <asm/sigcontext.h>
>  #endif])
>  
> +
> +dnl stack trace with libunwind
> +AC_ARG_WITH([libunwind],
> +	    [AS_HELP_STRING([--with-libunwind],
> +			    [libunwind is used to display system call stacktrace])],
> +	    [case "${withval}" in
> +	     (yes|no) with_libunwind=$withval;;
> +	     (*)      with_libunwind=yes
> +		      libunwind_CPPFLAGS="-I${withval}/include"
> +		      libunwind_LDFLAGS="-L${withval}/lib" ;;
> +	     esac],
> +	    [with_libunwind=check])
> +
> +AS_IF([test "x$with_libunwind" != "xno"],
> +	[saved_CPPFLAGS="${CPPFLAGS}"
> +	CPPFLAGS="${CPPFLAGS} ${libunwind_CPPFLAGS}"
> +	AC_CHECK_HEADERS([libunwind-ptrace.h],[],
> +			 [if test "x$with_libunwind" != "xcheck" ; then
> +			     AC_MSG_FAILURE([Unable to find libunwind-ptrace.h header])
> +			  fi])
> +	AC_CHECK_HEADERS([libunwind.h],[],
> +			 [if test "x$with_libunwind" != "xcheck" ; then
> +			     AC_MSG_FAILURE([Unable to find libunwind.h header])
> +			  fi])
> +	CPPFLAGS="${saved_CPPFLAGS}" ])
> +
> +
> +
> +if test "x$ac_cv_header_libunwind_ptrace_h" = "xyes" &&
> +	test "x$ac_cv_header_libunwind_h" = "xyes"; then
> +
> +	dnl code is taken from ltrace
> +	case "${host_cpu}" in
> +		arm*|sa110)         UNWIND_ARCH="arm" ;;
> +		i?86)               UNWIND_ARCH="x86" ;;
> +		powerpc)            UNWIND_ARCH="ppc32" ;;
> +		powerpc64)          UNWIND_ARCH="ppc64" ;;
> +		mips*)              UNWIND_ARCH="mips" ;;
> +		*)                  UNWIND_ARCH="${host_cpu}" ;;
> +	esac
> +
> +	saved_LDFLAGS="${LDFLAGS}"
> +	LDFLAGS="${LDFLAGS} ${libunwind_LDFLAGS}"
> +	AC_CHECK_LIB([unwind], [backtrace],
> +		     [libunwind_LIBS="-lunwind"],
> +		     [if test "x$with_libunwind" != "xcheck" ; then
> +			AC_MSG_FAILURE([Unable to find libunwind])
> +		      fi])
> +        AC_CHECK_LIB([unwind-generic], [_U${UNWIND_ARCH}_create_addr_space],
> +		     [libunwind_LIBS="-lunwind-generic $libunwind_LIBS"],
> +		     [if test "x$with_libunwind" != "xcheck" ; then
> +		        AC_MSG_FAILURE([Unable to find libunwind-generic])
> +		      fi],
> +		     [$libunwind_LIBS])
> +	AC_CHECK_LIB([unwind-ptrace], [_UPT_create],
> +		     [libunwind_LIBS="-lunwind-ptrace $libunwind_LIBS"],
> +		     [if test "x$with_libunwind" != "xcheck" ; then
> +		        AC_MSG_FAILURE([Unable to find libunwind-ptrace])
> +		      fi],
> +		     [$libunwind_LIBS])
> +	LDFLAGS="${saved_LDFLAGS}"
> +
> +	dnl we have all the dependencies we need we can activate stack tracing
> +	AC_SUBST(libunwind_LIBS)
> +	AC_SUBST(libunwind_LDFLAGS)
> +	AC_SUBST(libunwind_CPPFLAGS)
> +fi
> +
> +dnl enable libunwind
> +if test "x$ac_cv_lib_unwind_ptrace__UPT_create" == "xyes" &&
> +	eval test \"x\$ac_cv_lib_unwind_generic__U"${UNWIND_ARCH}"_create_addr_space\" == "xyes" &&
> +	test "x$ac_cv_lib_unwind_backtrace" == "xyes"; then
> +	AC_DEFINE([LIB_UNWIND], 1, [Compile stack tracing functionality])
> +	AC_MSG_NOTICE([Enabled stack tracing])
> +	with_libunwind="yes"
> +fi
> +AM_CONDITIONAL([LIB_UNWIND], [test "x$with_libunwind" == "xyes"])
> +
> +
>  AC_CHECK_MEMBERS([struct utsname.domainname],,, [#include <sys/utsname.h>])
>  
>  AC_CHECK_DECLS([sys_errlist])
> diff --git a/defs.h b/defs.h
> index 964636b..1b1fa8d 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -414,6 +414,33 @@ typedef struct ioctlent {
>  	unsigned long code;
>  } struct_ioctlent;
>  
> +
> +#ifdef LIB_UNWIND
> +
> +/* keep a sorted array of cache entries, so that we can binary search
> + * through it
> + */
> +struct mmap_cache_t {
> +	/**
> +	 * example entry:
> +	 * 7fabbb09b000-7fabbb09f000 r--p 00179000 fc:00 1180246 /lib/libc-2.11.1.so
> +	 *
> +	 * start_addr  is 0x7fabbb09b000
> +	 * end_addr    is 0x7fabbb09f000
> +	 * mmap_offset is 0x179000
> +	 * binary_filename is "/lib/libc-2.11.1.so"
> +	 */
> +	unsigned long start_addr;
> +	unsigned long end_addr;
> +	unsigned long mmap_offset;
> +	char* binary_filename;
> +};
> +
> +
> +/* if this is true do the stack trace for every system call */
> +extern bool use_libunwind;
> +#endif
> +
>  /* Trace Control Block */
>  struct tcb {
>  	int flags;		/* See below for TCB_ values */
> @@ -439,6 +466,12 @@ struct tcb {
>  	struct timeval etime;	/* Syscall entry time */
>  				/* Support for tracing forked processes: */
>  	long inst[2];		/* Saved clone args (badly named) */
> +
> +#ifdef LIB_UNWIND
> +	struct mmap_cache_t* mmap_cache;
> +	unsigned int mmap_cache_size;
> +	struct UPT_info* libunwind_ui;
> +#endif
>  };
>  
>  /* TCB flags */
> @@ -724,6 +757,15 @@ extern void tv_sub(struct timeval *, struct timeval *, struct timeval *);
>  extern void tv_mul(struct timeval *, struct timeval *, int);
>  extern void tv_div(struct timeval *, struct timeval *, int);
>  
> +#ifdef LIB_UNWIND
> +/**
> + * print stack (-k flag) memory allocation and deallocation
> + */
> +extern void alloc_mmap_cache(struct tcb* tcp);
> +extern void delete_mmap_cache(struct tcb* tcp);
> +extern void print_stacktrace(struct tcb* tcp);
> +#endif
> +
>  /* Strace log generation machinery.
>   *
>   * printing_tcp: tcb which has incomplete line being printed right now.
> diff --git a/mem.c b/mem.c
> index ef273c7..b3c6abe 100644
> --- a/mem.c
> +++ b/mem.c
> @@ -175,6 +175,11 @@ static int
>  print_mmap(struct tcb *tcp, long *u_arg, unsigned long long offset)
>  {
>  	if (entering(tcp)) {
> +#ifdef LIB_UNWIND
> +		if (use_libunwind)
> +			delete_mmap_cache(tcp);
> +#endif
> +
>  		/* addr */
>  		if (!u_arg[0])
>  			tprints("NULL, ");
> @@ -304,6 +309,11 @@ sys_munmap(struct tcb *tcp)
>  		tprintf("%#lx, %lu",
>  			tcp->u_arg[0], tcp->u_arg[1]);
>  	}
> +
> +#ifdef LIB_UNWIND
> +	if (exiting(tcp) && use_libunwind)
> +		delete_mmap_cache(tcp);
> +#endif
>  	return 0;
>  }
>  
> @@ -315,6 +325,11 @@ sys_mprotect(struct tcb *tcp)
>  			tcp->u_arg[0], tcp->u_arg[1]);
>  		printflags(mmap_prot, tcp->u_arg[2], "PROT_???");
>  	}
> +
> +#ifdef LIB_UNWIND
> +	if (exiting(tcp) && use_libunwind)
> +		delete_mmap_cache(tcp);
> +#endif
>  	return 0;
>  }
>  
> diff --git a/process.c b/process.c
> index e2fa25b..e058bbb 100644
> --- a/process.c
> +++ b/process.c
> @@ -992,6 +992,13 @@ sys_execve(struct tcb *tcp)
>  			tprints("]");
>  		}
>  	}
> +
> +
> +#ifdef LIB_UNWIND
> +	if (exiting(tcp) && use_libunwind)
> +		delete_mmap_cache(tcp);
> +#endif
> +
>  	return 0;
>  }
>  
> @@ -1209,6 +1216,13 @@ sys_waitid(struct tcb *tcp)
>  				printrusage(tcp, tcp->u_arg[4]);
>  		}
>  	}
> +
> +
> +#ifdef LIB_UNWIND
> +	if (exiting(tcp) && use_libunwind)
> +		delete_mmap_cache(tcp);
> +#endif
> +
>  	return 0;
>  }
>  
> diff --git a/strace.1 b/strace.1
> index 6ca4bda..e6373c0 100644
> --- a/strace.1
> +++ b/strace.1
> @@ -39,7 +39,7 @@
>  strace \- trace system calls and signals
>  .SH SYNOPSIS
>  .B strace
> -[\fB-CdffhiqrtttTvVxxy\fR]
> +[\fB-CdffhikqrtttTvVxxy\fR]
>  [\fB-I\fIn\fR]
>  [\fB-b\fIexecve\fR]
>  [\fB-e\fIexpr\fR]...
> @@ -306,6 +306,9 @@ Print all non-ASCII strings in hexadecimal string format.
>  .B \-xx
>  Print all strings in hexadecimal string format.
>  .TP
> +.B \-k
> +Print the execution stack trace of the traced processes after each system call.
> +.TP
>  .B \-y
>  Print paths associated with file descriptor arguments.
>  .TP
> diff --git a/strace.c b/strace.c
> index 32a3f5e..5c46d7f 100644
> --- a/strace.c
> +++ b/strace.c
> @@ -50,6 +50,13 @@ extern char **environ;
>  extern int optind;
>  extern char *optarg;
>  
> +#ifdef LIB_UNWIND
> +# include <libunwind-ptrace.h>
> +
> +/* if this is true do the stack trace for every system call */
> +bool use_libunwind = false;
> +unw_addr_space_t libunwind_as;
> +#endif
>  
>  #if defined __NR_tkill
>  # define my_tkill(tid, sig) syscall(__NR_tkill, (tid), (sig))
> @@ -231,6 +238,10 @@ usage: strace [-CdffhiqrtttTvVxxy] [-I n] [-e expr]...\n\
>  -E var -- remove var from the environment for command\n\
>  -P path -- trace accesses to path\n\
>  "
> +#ifdef LIB_UNWIND
> +"-k obtain stack trace between each syscall\n\
> +"
> +#endif
>  /* ancient, no one should use it
>  -F -- attempt to follow vforks (deprecated, use -f)\n\
>   */
> @@ -685,6 +696,15 @@ alloctcb(int pid)
>  #if SUPPORTED_PERSONALITIES > 1
>  			tcp->currpers = current_personality;
>  #endif
> +
> +#ifdef LIB_UNWIND
> +			if (use_libunwind) {
> +				tcp->libunwind_ui = _UPT_create(tcp->pid);
> +				if (!tcp->libunwind_ui)
> +				    die_out_of_memory();
> +			}
> +#endif
> +
>  			nprocs++;
>  			if (debug_flag)
>  				fprintf(stderr, "new tcb for pid %d, active tcbs:%d\n", tcp->pid, nprocs);
> @@ -721,6 +741,12 @@ droptcb(struct tcb *tcp)
>  	if (printing_tcp == tcp)
>  		printing_tcp = NULL;
>  
> +#ifdef LIB_UNWIND
> +	if (use_libunwind) {
> +		delete_mmap_cache(tcp);
> +		_UPT_destroy(tcp->libunwind_ui);
> +	}
> +#endif
>  	memset(tcp, 0, sizeof(*tcp));
>  }
>  
> @@ -1642,6 +1668,9 @@ init(int argc, char *argv[])
>  	qualify("signal=all");
>  	while ((c = getopt(argc, argv,
>  		"+b:cCdfFhiqrtTvVxyz"
> +#ifdef LIB_UNWIND
> +		"k"
> +#endif
>  		"D"
>  		"a:e:o:O:p:s:S:u:E:P:I:")) != EOF) {
>  		switch (c) {
> @@ -1744,6 +1773,11 @@ init(int argc, char *argv[])
>  		case 'u':
>  			username = strdup(optarg);
>  			break;
> +#ifdef LIB_UNWIND
> +		case 'k':
> +			use_libunwind = true;
> +			break;
> +#endif
>  		case 'E':
>  			if (putenv(optarg) < 0)
>  				die_out_of_memory();
> @@ -1775,6 +1809,15 @@ init(int argc, char *argv[])
>  		error_msg_and_die("-D and -p are mutually exclusive");
>  	}
>  
> +#ifdef LIB_UNWIND
> +	if (use_libunwind) {
> +		libunwind_as = unw_create_addr_space(&_UPT_accessors, 0);
> +		if (!libunwind_as) {
> +			error_msg_and_die("Fatal error: unable to create address space for stack tracing\n");
> +		}
> +	}
> +#endif
> +
>  	if (!followfork)
>  		followfork = optF;
>  
> diff --git a/syscall.c b/syscall.c
> index 1b49bb3..0c23e40 100644
> --- a/syscall.c
> +++ b/syscall.c
> @@ -2683,6 +2683,15 @@ trace_syscall_exiting(struct tcb *tcp)
>  	dumpio(tcp);
>  	line_ended();
>  
> +#ifdef LIB_UNWIND
> +	if (use_libunwind) {
> +		if (!tcp->mmap_cache) {
> +			alloc_mmap_cache(tcp);
> +		}
> +		print_stacktrace(tcp);
> +	}
> +#endif
> +
>   ret:
>  	tcp->flags &= ~TCB_INSYSCALL;
>  	return 0;
> diff --git a/unwind.c b/unwind.c
> new file mode 100644
> index 0000000..5dc0175
> --- /dev/null
> +++ b/unwind.c
> @@ -0,0 +1,230 @@
> +/*
> + * Copyright (c) 2013 Luca Clementi <luc...@gm...>
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. The name of the author may not be used to endorse or promote products
> + *    derived from this software without specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
> + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
> + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
> + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
> + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
> + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + */
> +
> +#include "defs.h"
> +
> +
> +#include <limits.h>
> +
> +#include <libunwind.h>
> +
> +
> +extern unw_addr_space_t libunwind_as;
> +/*
> + * caching of /proc/ID/maps for each process to speed up stack tracing
> + *
> + * The cache must be refreshed after some syscall: mmap, mprotect, munmap, execve
> + */
> +void
> +alloc_mmap_cache(struct tcb* tcp)
> +{
> +	unsigned long start_addr, end_addr, mmap_offset;
> +	char filename[sizeof ("/proc/0123456789/maps")];
> +	char buffer[PATH_MAX + 80];
> +	char binary_path[PATH_MAX];
> +	struct mmap_cache_t *cur_entry, *prev_entry;
> +	/* start with a small dynamically-allocated array and then expand it */
> +	size_t cur_array_size = 10;
> +	struct mmap_cache_t *cache_head = malloc(cur_array_size * sizeof(*cache_head));
> +	if (!cache_head)
> +		die_out_of_memory();
> +
> +	sprintf(filename, "/proc/%d/maps", tcp->pid);
> +
> +	FILE* f = fopen(filename, "r");
> +	if (!f)
> +		perror_msg_and_die("Can't open %s", filename);
> +	while (fgets(buffer, sizeof(buffer), f) != NULL) {
> +		binary_path[0] = '\0'; // 'reset' it just to be paranoid
> +
> +		sscanf(buffer, "%lx-%lx %*c%*c%*c%*c %lx %*x:%*x %*d %[^\n]", &start_addr,
> +			&end_addr, &mmap_offset, binary_path);
> +
> +		/* ignore special 'fake files' like "[vdso]", "[heap]", "[stack]", */
> +		if (binary_path[0] == '[') {
> +			continue;
> +		}
> +
> +		if (binary_path[0] == '\0') {
> +			continue;
> +		}
> +
> +		if (end_addr < start_addr)
> +			perror_msg_and_die("Unrecognized maps file format %s", filename);
> +
> +		cur_entry = &cache_head[tcp->mmap_cache_size];
> +		cur_entry->start_addr = start_addr;
> +		cur_entry->end_addr = end_addr;
> +		cur_entry->mmap_offset = mmap_offset;
> +		cur_entry->binary_filename = strdup(binary_path);
> +
> +		/* sanity check to make sure that we're storing non-overlapping regions in
> +		 * ascending order
> +		 */
> +		if (tcp->mmap_cache_size > 0) {
> +			prev_entry = &cache_head[tcp->mmap_cache_size - 1];
> +			if (prev_entry->start_addr >= cur_entry->start_addr)
> +				perror_msg_and_die("Overlaying memory region in %s", filename);
> +			if (prev_entry->end_addr > cur_entry->start_addr)
> +				perror_msg_and_die("Overlaying memory region in %s", filename);
> +		}
> +		tcp->mmap_cache_size++;
> +
> +		/* resize doubling its size */
> +		if (tcp->mmap_cache_size >= cur_array_size) {
> +			cur_array_size *= 2;
> +			cache_head = realloc(cache_head, cur_array_size * sizeof(*cache_head));
> +			if (!cache_head)
> +				die_out_of_memory();
> +		}
> +	}
> +	fclose(f);
> +	tcp->mmap_cache = cache_head;
> +}
> +
> +/* deleting the cache */
> +void
> +delete_mmap_cache(struct tcb* tcp)
> +{
> +	unsigned int i;
> +	for (i = 0; i < tcp->mmap_cache_size; i++) {
> +		free(tcp->mmap_cache[i].binary_filename);
> +	}
> +	free(tcp->mmap_cache);
> +	tcp->mmap_cache = NULL;
> +	tcp->mmap_cache_size = 0;
> +}
> +
> +
> +
> +/*
> + * use libunwind to unwind the stack and print a backtrace
> + *
> + * Pre-condition: tcp->mmap_cache is already initialized
> + */
> +void
> +print_stacktrace(struct tcb* tcp)
> +{
> +	unw_word_t ip;
> +	unw_cursor_t cursor;
> +	unw_word_t function_off_set;
> +	int stack_depth = 0, ret_val;
> +	/* these are used for the binary search through the mmap_chace */
> +	unsigned int lower, upper, mid;
> +	size_t symbol_name_size = 40;
> +	char * symbol_name;
> +	struct mmap_cache_t* cur_mmap_cache;
> +	unsigned long true_offset;
> +
> +	symbol_name = malloc(symbol_name_size);
> +	if (!symbol_name)
> +		die_out_of_memory();
> +
> +	if (unw_init_remote(&cursor, libunwind_as, tcp->libunwind_ui) < 0)
> +		perror_msg_and_die("Can't initiate libunwind");
> +
> +	do {
> +		/* looping on the stack frame */
> +		if (unw_get_reg(&cursor, UNW_REG_IP, &ip) < 0)
> +			perror_msg("Can't walk the stack of process %d", tcp->pid);
> +
> +		lower = 0;
> +		upper = tcp->mmap_cache_size - 1;
> +
> +		while (lower <= upper) {
> +			/* find the mmap_cache and print the stack frame */
> +			mid = (unsigned int)((upper + lower) / 2);
> +			cur_mmap_cache = &tcp->mmap_cache[mid];
> +
> +			if (ip >= cur_mmap_cache->start_addr &&
> +				ip < cur_mmap_cache->end_addr) {
> +
> +				for (;;) {
> +					symbol_name[0] = '\0';
> +					ret_val = unw_get_proc_name(&cursor, symbol_name,
> +						symbol_name_size, &function_off_set);
> +					if (ret_val != -UNW_ENOMEM)
> +						break;
> +					symbol_name_size *= 2;
> +					symbol_name = realloc(symbol_name, symbol_name_size);
> +					if (!symbol_name)
> +						die_out_of_memory();
> +				}
> +
> +				true_offset = ip - cur_mmap_cache->start_addr + cur_mmap_cache->mmap_offset;
> +				if (symbol_name[0]) {
> +					/*
> +					 * we want to keep the format used by backtrace_symbols from the glibc
> +					 *
> +					 * ./a.out() [0x40063d]
> +					 * ./a.out() [0x4006bb]
> +					 * ./a.out() [0x4006c6]
> +					 * /lib64/libc.so.6(__libc_start_main+0xed) [0x7fa2f8a5976d]
> +					 * ./a.out() [0x400569]
> +					 */
> +					tprintf(" > %s(%s+0x%lx) [0x%lx]\n", cur_mmap_cache->binary_filename,
> +						symbol_name, function_off_set, true_offset);
> +					line_ended();
> +				} else {
> +					tprintf(" > %s() [0x%lx]\n", cur_mmap_cache->binary_filename, true_offset);
> +					line_ended();
> +				}
> +
> +				break; /* stack frame printed */
> +			}
> +			else if (mid == 0) {
> +				/**
> +				 * there is a bug in libunwind >= 1.0
> +				 * after a set_tid_address syscall unw_get_reg returns IP=0
> +				 */
> +				tprintf(" > backtracing_error\n");
> +				line_ended();
> +				goto ret;
> +			}
> +			else if (ip < cur_mmap_cache->start_addr)
> +				upper = mid - 1;
> +
> +			else
> +				lower = mid + 1;
> +
> +		}
> +		if (lower > upper) {
> +			tprintf(" > backtracing_error [0x%lx]\n", ip);
> +			line_ended();
> +			goto ret;
> +		}
> +
> +		ret_val = unw_step(&cursor);
> +
> +		if (++stack_depth > 255) {
> +			tprintf("libunwind warning: stack frame greater than 255 aborting backtracing\n");
> +			line_ended();
> +			break;
> +		}
> +	} while (ret_val > 0);
> +ret:
> +	free(symbol_name);
> +}
> -- 
> 1.7.9.5
> 
> 
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