Symbols/blocks questions

Vladimir Prus
2009-09-19T11:52:05Z

I am trying to port some MI improvement from the Apple GDB,
and got some questions about symbol/block handling. I'd
appreciate if somebody comment on it.

1. Given 'struct block *b', is it true that

block_for_pc (b.startaddr) == b

?

2. Uness I am mistaken, in case of lines inside templates,
inline functions, and constructors, decode_line_1 returns
just one sal. (And breakpoint.c explicitly expands thsoe in
expand_line_sal). In what cases will decode_line_1 actually
return multiple sals? For overloaded functions? Anything else?
Would it be sensible, eventually, to make decode_line_1
return all locations corresponding to file:line?

3. The code below, from Apple GDB, first calls decode_line_1
and then checks, for each sal, if the line passed to decode_line_1
is less then sal.line. How could this happen at all? I though that
if I ask decode_line_1 for line 10, then either it returns sals
for line 10, or it returns no sal at all.

(For context, the purpose of the code is, given file:line, to find
block in which variables should be looked up and evaluated, for -var-create)

Thanks,
Volodya

TRY_CATCH (except, RETURN_MASK_ALL)
{
/* The variable 's' will be advanced by decode_line_1. */
char *s = block_addr;
sals = decode_line_1 (&s, 1, (struct symtab *) NULL, 0, NULL,
NULL);
}

if (except.reason >= 0 && sals.nelts >= 1)
{
old_chain = make_cleanup (xfree, sals.sals);

/* Default to global scope unless we find a better match. */
var_type = NO_FRAME_NEEDED;
block = BLOCKVECTOR_BLOCK (BLOCKVECTOR (sals.sals[0].symtab),
GLOBAL_BLOCK);

unsigned long line = 0;
char *line_number_str = colon + 1;
if (strlen (line_number_str) > 0)
line = strtoul (line_number_str, NULL, 0);

/* Get the currently selected frame for reference. */
struct frame_info *selected_frame = get_selected_frame (NULL);
if (selected_frame)
{
unsigned i;
struct symbol *func_sym;
func_sym = get_frame_function (selected_frame);
if (func_sym)
/* Iterate through all symtab_and_line structures
returned and find the one that has the same
function symbol as our frame. */
for (i = 0; i < sals.nelts; i++)
{
struct symbol *sal_sym =
find_pc_sect_function (sals.sals[i].pc,
sals.sals[i].section);

if (func_sym == sal_sym)
{
/* If the requested line is less than the line
found in the matching symtab_and_line
struct then we must use a global or static
as the scope since it doesn't fall within
the symtab_and_line struct that was
returned. */
if (line && line < sal_sym->line)
{
/* Use a global scope. */
var_type = NO_FRAME_NEEDED;
block = BLOCKVECTOR_BLOCK
(BLOCKVECTOR (sals.sals[i].symtab),
GLOBAL_BLOCK);
}
else
{
/* We got a valid block match. */
var_type = USE_BLOCK_IN_FRAME;
block = block_for_pc (sals.sals[i].pc);
break;
}
}
}
}
}