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

Yao Qi
2018-01-16T17:12:25Z

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.

--
Yao (齐尧)