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Re: [patch] Fix to processing end of function stab in dbxread.c
On Thu, Jul 11, 2002 at 11:10:28AM -0700, Jim Ingham wrote:
> Daniel,
>
> We are talking about two different things here - I am talking about
> converting the value in the blank FUN stab that marks the end of a
> function to a read address, NOT correcting an SLINE stab. That may
> seem confusing given that I was talking about linetables, so I will
> give my previous explanation in a little more detail.
Thanks for the excellent explanation.
<snip explanation of the original SLINE problem, which I understand>
> Fred's fix was to emit a fake linetable entry - with linenumber 0, when
> he sees the end of function stab. That way, in the linetable there is
> just a region with no associated linenumbers from the end of the
> function to 00031fd4. The problem was getting "the end of the
> function" from the data in the null FUN stab. The value of the stab is
> the offset from the beginning of the function. He was adding that to
> function_start_offset which according to the comment in the file is NOT
> the address of the last function on any system but Solaris. It is the
> offset to the text section on other platforms, (which is clever,
> because then it is the correct thing to use to relocate the addresses
> in the SLINE entries on all platforms). But it is not an appropriate
> thing to add to the offset from the end function stab.
>
> Note also that in the one other place where we get the real address
> from the end fun stab (dbxread.c around 1726), we do:
>
> /* See if this is an end of function stab. */
> if (pst && nlist.n_type == N_FUN && *namestring == '\000')
> {
> CORE_ADDR valu;
>
> /* It's value is the size (in bytes) of the function for
> function relative stabs, or the address of the function's
> end for old style stabs. */
> valu = nlist.n_value + last_function_start;
> if (TEXTHIGH (pst) == 0 || valu > TEXTHIGH (pst))
> TEXTHIGH (pst) = valu;
> break;
> }
>
> again using last_function_start, not function_start_offset.
You've switched functions. That code is in read_dbx_symtab. There was
no variable in process_one_symbol by that name until quite recently.
They do have the same meaning however. That's what I meant about your
archeology being wrong. The comment that function_start_offset is
only correct for Solaris is also wrong; I can verify that it is correct
on GNU/Linux. That's not your fault, though, the comments in dbxread.c
range from mediocre to misleading. What comments referencing Solaris 2
(rather than referencing something about Sun's lame tools) often
mean is "on SVR4-ish systems".
I judge from your example that MacOSX has resolved addresses attached
to N_SLINE stabs, but not in ending N_FUN stabs? GDB assumes that
function_start_offset applies to both of them equally (and it will be
zero if we expect both to be resolved). On GNU/Linux both N_SLINE and
final N_FUN have offsets within the function. I suspect that on some
Solaris variant N_SLINE and final N_FUN will both have resolved values.
In that case using last_function_start + valu will put us well outside
of the actual function, causing mayhem.
--
Daniel Jacobowitz Carnegie Mellon University
MontaVista Software Debian GNU/Linux Developer