Re: [PING][PATCH PR gdb/18071] TLS variables can't be resolved on aarch64-linux-gnu

Weimin Pan
2018-01-17T01:05:50Z

On 1/16/2018 9:12 AM, Yao Qi wrote:
> Wei-min Pan <weimin.pan@oracle.com> writes:
>
>>> Function info_address_command() handles the "info address" command and
>>> calls lookup_minimal_symbol_and_objfile() to find sym's symbol entry in
>>> mininal symbol table if SYMBOL_COMPUTED_OPS (sym) is false. Problem is
>>> that function lookup_minimal_symbol_and_objfile() only looked up an
>>> objfile's minsym ordinary hash table, not its demangled hash table, which
>>> was the reason why the C++ name was not found.
> lookup_minimal_symbol_and_objfile is documented as "only checks the
> linkage name" in minsyms.h,
>
> /* Find the minimal symbol named NAME, and return both the minsym
> struct and its objfile. This only checks the linkage name. */
>
> struct bound_minimal_symbol lookup_minimal_symbol_and_objfile (const char *);
>
>>> The fix is to call lookup_minimal_symbol(), which already looks up entries
>>> in both minsym's hash tables, to find names when traversing the object file
>>> list in lookup_minimal_symbol_and_objfile().
> so, it is incorrect to extend it to search demangled name. If I set a
> breakpoint on lookup_minimal_symbol_and_objfile,
>
> (gdb) info address K::another_thread_local
>
> Breakpoint 1, lookup_minimal_symbol_and_objfile (name=0x621000136e40 "K::another_thread_local") at gdb/minsyms.c:1012
> 1012 unsigned int hash = msymbol_hash (name) % MINIMAL_SYMBOL_HASH_SIZE;
> (gdb) up
> #1 0x0000000000af7690 in info_address_command (exp=0x604000023f5d "K::another_thread_local", from_tty=1)
> at gdb/printcmd.c:1567
> 1567 msym = lookup_minimal_symbol_and_objfile (SYMBOL_LINKAGE_NAME (sym));
>
> The problem to me is that why SYMBOL_LINKAGE_NAME (sym) is
> "K::another_thread_local", which is a demangled one. The symbol's name
> is set in dwarf2read.c:new_symbol_full,
>
> /* Cache this symbol's name and the name's demangled form (if any). */
> SYMBOL_SET_LANGUAGE (sym, cu->language, &objfile->objfile_obstack);
> linkagename = dwarf2_physname (name, die, cu);
> SYMBOL_SET_NAMES (sym, linkagename, strlen (linkagename), 0, objfile);
>
> however, dwarf2_physname doesn't return the linkage name, so the
> symbol's linkagename is set incorrectly. I think the right fix would be
> call other function to get linkagename, maybe, dw2_linkage_name? I
> don't know.
dwarf2_physname() does call dw2_linkage_name(). But since the class member,
i.e.Â  another_thread_local, does not contain either DW_AT_linkage_name or
DW_AT_MIPS_linkage_name attribute, its canonicalized name gets returned.