Compilation Unit name

[SASHA NICOLAS DA ROCHA PINHEIRO]

Hello guys,
I work for Dyninst, and I am moving from libdwarf to libdw. I am trying  to get 
the compilation unit name calling dwarf_nextcu, dwarf_offdie and  
dwarf_diename, but it won't work as it works with libdwarf. I got NULL  as 
return from dwarf_diename. When I print the error messages after each  of these 
three function calls, I get no errors for the first two and an  "invalid dwarf" 
for the third one. Can you help me with it?
Below I present the snippet where I am doing the calls, both with libdwarf and 
libdw.

Sasha Nicolas



//Using libdwarf
bool Object::fix_global_symbol_modules_static_dwarf()
{
    /* Initialize libdwarf. */
    ::Dwarf **dbg_ptr = dwarf->type_dbg();
    if (!dbg_ptr)
    return false;
    ::Dwarf *dbg = *dbg_ptr;
    std::set dies_seen;
    dwarf_parse_aranges(dbg, dies_seen);

    /* Iterate over the compilation-unit headers. */
    size_t cu_header_size;
    for(Dwarf_Off cu_off = 0, next_cu_off;
    dwarf_nextcu(dbg, cu_off, &next_cu_off, &cu_header_size,
    NULL, NULL, NULL) == 0;
    cu_off = next_cu_off)
    {
    cerr << "Error message:" << dwarf_errmsg(-1) << endl;
    Dwarf_Die cu_die, *cu_die_p;
    cu_die_p = dwarf_offdie(dbg, next_cu_off /*cu_die_off*/, &cu_die);
    cerr << "Error message:" << dwarf_errmsg(-1) << endl;

    if(cu_die_p == NULL) continue;
    if(dies_seen.find(next_cu_off/* cu_die_off*/) != dies_seen.end()) 
continue;

    std::string modname;
    auto diename = dwarf_diename(&cu_die);
    cerr << "Error message:" << dwarf_errmsg(-1) << endl;
    if(diename == NULL)
    {
    modname = associated_symtab->file(); // default module
    }
    else
    {
    modname = diename;
    }

...


//Using libdwarf

bool Object::fix_global_symbol_modules_static_dwarf()
{
    /* Initialize libdwarf. */
    Dwarf_Debug *dbg_ptr = dwarf->type_dbg();
    if (!dbg_ptr)
    return false;
    Dwarf_Debug dbg = *dbg_ptr;
    std::set dies_seen;
    Dwarf_Off cu_die_off;
    Dwarf_Die cu_die;
    dwarf_parse_aranges(dbg, dies_seen);
    /* Iterate over the compilation-unit headers. */
    while (dwarf_next_cu_header_c(dbg, Dwarf_Bool(true),
  NULL,NULL,NULL,NULL,NULL,NULL,NULL,
  &cu_die_off, NULL) == DW_DLV_OK )
    {
    int status = dwarf_siblingof_b(dbg, NULL, Dwarf_Bool(true), &cu_die, 
NULL);
    assert(status == DW_DLV_OK);
    if(dies_seen.find(cu_die_off) != dies_seen.end()) continue;
    std::string modname;
    if(!DwarfWalker::findDieName(dbg, cu_die, modname))
    {
    modname = associated_symtab->file(); // default module
    }

Re: Compilation Unit name

[Josh Stone]

On 03/16/2017 03:03 PM, SASHA NICOLAS DA ROCHA PINHEIRO wrote:
> /* Iterate over the compilation-unit headers. */
> size_t cu_header_size;
> for(Dwarf_Off cu_off = 0, next_cu_off;
> dwarf_nextcu(dbg, cu_off, &next_cu_off, &cu_header_size,
> NULL, NULL, NULL) == 0;
> cu_off = next_cu_off)
> {
> cerr << "Error message:" << dwarf_errmsg(-1) << endl;
> Dwarf_Die cu_die, *cu_die_p;
> cu_die_p = dwarf_offdie(dbg, next_cu_off /*cu_die_off*/, &cu_die);

I don't understand why you're using next_cu_off here.

The die offset is cu_off + cu_header_size.

Also, when you get around to it, note there's a different
dwarf_offdie_types when you're parsing .debug_types.

Re: Compilation Unit name

[Josh Stone]

Stick to plain text, not HTML, if you want to reach the list.

On 03/16/2017 03:44 PM, SASHA NICOLAS DA ROCHA PINHEIRO wrote:
> I had that before, and it didn't work, then I empirically changed to
> next_cu_off because it contained the same offset I was supposed to get
> when I compared to the libdwarf execution. 

What you have called cu_die_off is *not* a die offset!  In libdwarf.h
that argument is called next_cu_header_offset, which is why it has the
same value as the next_cu_off you're getting from libdw.

> We already discarded the option of using dwarf_offdie_types since
> previously, with libdwarf, it was passed true to:

That's fine and correct.  You shouldn't use dwarf_offdie_types now, I
was trying to preempt a future problem.  Sorry for adding confusion.