------- Comment #11 from davek at gcc dot gnu dot org 2009-09-15 14:53 -------
The bogus const info is added in at the end of this call chain, when generating
the var die:
#0 0x004d0679 in add_const_value_attribute (die=0x7fcbd660, rtl=0x7fd20270)
at /gnu/gcc/gcc/gcc/tree.h:182
#1 0x004d25ec in add_location_or_const_value_attribute (die=0x7fcbd660,
decl=0x7fe19e40, attr=DW_AT_location) at /gnu/gcc/gcc/gcc/tree.h:182
#2 0x004da1f2 in gen_variable_die (decl=0x7fe19e40, origin=0x0,
context_die=0x7fcbbe50) at /gnu/gcc/gcc/gcc/tree.h:182
#3 0x004deda3 in gen_decl_die (decl=0x7fe19e40, origin=0x0,
context_die=0x7fcbbe50) at /gnu/gcc/gcc/gcc/tree.h:182
#4 0x004dd3ed in process_scope_var (stmt=0x7fcb2060, decl=0x7fe19e40,
origin=0x0, context_die=0x7fcbbe50) at /gnu/gcc/gcc/gcc/tree.h:182
#5 0x004dd470 in decls_for_scope (stmt=0x7fcb2060, context_die=0x7fcbbe50,
depth=0) at /gnu/gcc/gcc/gcc/tree.h:182
#6 0x004d91d8 in gen_subprogram_die (decl=0x7fdfb500, context_die=0x7fe03678)
at /gnu/gcc/gcc/gcc/tree.h:182
#7 0x004dea1c in gen_decl_die (decl=0x7fdfb500, origin=0x0,
context_die=0x7fe03678) at /gnu/gcc/gcc/gcc/tree.h:182
#8 0x004dfb56 in dwarf2out_decl (decl=0x7fdfb500)
at /gnu/gcc/gcc/gcc/tree.h:182
#9 0x00834dbf in rest_of_handle_final () at /gnu/gcc/gcc/gcc/final.c:3131
In the above call stack, the rtx that is passed to add_const_value_attribute()
looks like this:
(gdb) call debug_rtx (rtl)
(symbol_ref:SI ("gomp_tls_data") [flags 0x42] <var_decl 0x7fe190c0
gomp_tls_data
>)
There is code in add_const_value_attribute() to avoid this problem already:
12789 /* Attach a DW_AT_const_value attribute for a variable or a parameter
which
12790 does not have a "location" either in memory or in a register. These
12791 things can arise in GNU C when a constant is passed as an actual
parameter
12792 to an inlined function. They can also arise in C++ where declared
12793 constants do not necessarily get memory "homes". */
12794
12795 static void
12796 add_const_value_attribute (dw_die_ref die, rtx rtl)
12797 {
12798 switch (GET_CODE (rtl))
12799 {
[ ... ]
12911 case SYMBOL_REF:
12912 if (GET_CODE (rtl) == SYMBOL_REF
12913 && SYMBOL_REF_TLS_MODEL (rtl) != TLS_MODEL_NONE)
12914 break;
12915 case LABEL_REF:
12916 add_AT_addr (die, DW_AT_const_value, rtl);
12917 VEC_safe_push (rtx, gc, used_rtx_array, rtl);
12918 break;
and indeed, it works by simply punting if the symbol ref in question points to
a TLS item, but the flags are wrong in the rtx that is passed in:
(symbol_ref:SI ("gomp_tls_data") [flags 0x42] <var_decl 0x7fe190c0
gomp_tls_data>)
This apparently has SYMBOL_REF_TLS_MODEL (rtl) == TLS_MODEL_NONE, so we never
bail out the escape hatch and end up calling add_AT_addr() to create the
DW_AT_const_value that needs relocating against the undefined symbol.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41357
