[RFC 2/2] Unwind: demangle symbol names

[Dmitry V. Levin]

On Tue, Dec 05, 2017 at 07:01:03PM +0900, Masatake YAMATO wrote:
> This patch is for demangling c++ symbols appeared in strack traces
> with using cplus_demangle in GNU libiberty library,
> 
> I'm not sure this is acceptable or not because this change introdues a depedency
> to a GPLv3+ library to strace.

There has to be a configure option, e.g. --with-libibery[=yes|no|check].

> This is an example of output of demangled stack trace:
> 
> fstat(5, {st_mode=S_IFREG|0664, st_size=0, ...}) = 0
>  > /usr/lib64/libc-2.25.so(__fxstat64+0x12) [0xffd62]
>  > /usr/lib64/libc-2.25.so(_IO_file_doallocate+0x5f) [0x717ff]
>  > /usr/lib64/libc-2.25.so(_IO_doallocbuf+0x79) [0x81699]
>  > /usr/lib64/libc-2.25.so(_IO_file_overflow+0x198) [0x807b8]
>  > /usr/lib64/libc-2.25.so(_IO_file_xsputn+0xbd) [0x7ed5d]
>  > /usr/lib64/libc-2.25.so(fwrite_unlocked+0x60) [0x7d800]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::EnvWrapper::StartThread+0x3b6) [0x48656]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::log::Writer::EmitPhysicalRecord+0x89) [0x28bc9]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::log::Writer::AddRecord+0x9e) [0x28d9e]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::DBImpl::Write+0x208) [0x1ce18]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::DB::Put+0x59) [0x192b9]
>  > /usr/lib64/libleveldb.so.1.18(leveldb::DBImpl::Put+0x1d) [0x1931d]

Yes, this looks nicer.

>  > /home/yamato/var/leveldb/doc/a.out(main+0x120) [0x1107]
>  > /usr/lib64/libc-2.25.so(__libc_start_main+0xea) [0x2088a]
>  > /home/yamato/var/leveldb/doc/a.out(_start+0x2a) [0xf3a]
> ---
>  Makefile.am  |  2 +-
>  configure.ac | 10 ++++++++++
>  unwind.c     | 18 ++++++++++++++++++
>  3 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile.am b/Makefile.am
> index 60376056..e69bd1fd 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -332,7 +332,7 @@ if USE_LIBUNWIND
>  strace_SOURCES += unwind.c
>  strace_CPPFLAGS += $(libunwind_CPPFLAGS)
>  strace_LDFLAGS += $(libunwind_LDFLAGS)
> -strace_LDADD += $(libunwind_LIBS)
> +strace_LDADD += $(libunwind_LIBS) $(libiberty_LIBS)
>  endif
>  
>  @CODE_COVERAGE_RULES@
> diff --git a/configure.ac b/configure.ac
> index fa451d84..b7ec9240 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -877,6 +877,16 @@ fi
>  AM_CONDITIONAL([USE_LIBUNWIND], [test "x$use_libunwind" = xyes])
>  AC_MSG_RESULT([$use_libunwind])
>  
> +libiberty_LIBS=
> +if test "x$use_libunwind" = xyes; then
> +   AC_CHECK_HEADERS([demangle.h],
> +     [AC_CHECK_LIB([iberty], [cplus_demangle],
> +       [libiberty_LIBS=-liberty
> +        AC_DEFINE([USE_DEMANGLE], 1, [Do demangling symbols when tracking stack])
> +       ])])
> +  AC_SUBST(libiberty_LIBS)
> +fi
> +
>  if test "$arch" = mips && test "$no_create" != yes; then
>  	mkdir -p linux/mips
>  	if $srcdir/linux/mips/genstub.sh linux/mips; then
> diff --git a/unwind.c b/unwind.c
> index 031795cc..bb357317 100644
> --- a/unwind.c
> +++ b/unwind.c
> @@ -29,6 +29,10 @@
>  #include <limits.h>
>  #include <libunwind-ptrace.h>
>  
> +#ifdef USE_DEMANGLE
> +#include <demangle.h>
> +#endif
> +
>  #ifdef _LARGEFILE64_SOURCE
>  # ifdef HAVE_FOPEN64
>  #  define fopen_for_input fopen64
> @@ -325,11 +329,25 @@ print_stack_frame(struct tcb *tcp,
>  					&function_offset);
>  			true_offset = ip - cur_mmap_cache->start_addr +
>  				cur_mmap_cache->mmap_offset;
> +
> +#ifdef USE_DEMANGLE
> +			char *demangled_name = cplus_demangle (*symbol_name, 0);
> +#endif
> +
>  			call_action(data,
>  				    cur_mmap_cache->binary_filename,
> +#ifdef USE_DEMANGLE
> +				    demangled_name? demangled_name: *symbol_name,
> +#else
>  				    *symbol_name,
> +#endif
>  				    function_offset,
>  				    true_offset);
> +#ifdef USE_DEMANGLE
> +			if (demangled_name)
> +				free (demangled_name);

Just free(demangled_name), no extra check for non-NULL is needed.


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