[Libunwind-devel] libunwind and split debug files

[Norbert Lange]

Hello,

I want to display stacktraces in cases of crashes, and libunwind is
incapable of following the gnu_debuglink for debug information, and
cant resolve function names. The configure option --enable-debug-frame
*does resolve the right debug file*, but only seems to use it for
something else.

Is this supposed to not work? Debug-infos can easily take dozens of
MB, so not stripping them is a annoying handicap.

I am running on Debian Stretch AMD64, taken the libunwind sources from
https://packages.debian.org/source/stretch/amd64/libunwind

libunwind 1.1 is configured and build with these options:
--with-pic --enable-cxx-exceptions --enable-minidebuginfo --enable-debug-frame

cat > unwind.cpp << 'EOF'
#include <cstdio>

#define UNW_LOCAL_ONLY
#include <libunwind.h>

static void show_backtrace (void) {
    unw_cursor_t cursor; unw_context_t uc;
    unw_word_t ip, sp;

    unw_getcontext(&uc);
    unw_init_local(&cursor, &uc);
    while (unw_step(&cursor) > 0) {
      unw_get_reg(&cursor, UNW_REG_IP, &ip);
      unw_get_reg(&cursor, UNW_REG_SP, &sp);
      char buffer[512];
      unw_word_t off = 0;
      if (unw_get_proc_name(&cursor, buffer, sizeof(buffer), &off) != 0)
          buffer[0] = '\0';
      printf ("ip = %lx, sp = %lx. %s (+%lu)\n", (long) ip, (long) sp,
buffer, (unsigned long)off);
    }
}

void foo2()
{
    show_backtrace();
}

void foo1()
{
    foo2();
}
int main(int argc, char **argv)
{
    foo1();
}
EOF
cat > Makefile << 'EOF'
all: unwind unwind_split unwind_split.dbg

unwind: unwind.cpp
$(CXX) $(CXXFLAGS) -lunwind -o "$@" $^


unwind_split unwind_split.dbg: unwind
objcopy --only-keep-debug "$<" unwind_split.dbg && \
 objcopy --strip-debug --strip-unneeded
--add-gnu-debuglink=unwind_split.dbg "$<" unwind_split || \
          rm -f unwind_split unwind_split.dbg

clean:
rm -f unwind unwind_split unwind_split.dbg
EOF