Hi George,
First, thanks for contributing! The current state of the debug info
emitted by gfortran is far from very good (not to mention work
required on gdb to make it understand Fortran better), so we're always
happy to fix this.
This patch fixes scope bug arising with Fortran symbols defined in
COMMON. They get emitted in the wrong debug scope unless they are
put on the symbol list associated with each function. Bug shows up
with stabs-type debug information and fixes that; other debug forms
possibly also a problem. Patch follows:
Unfortunately, I don't think we can apply this patch as such. For the
following simple code:
$ cat x.f90
program test
integer ii, jj
common /foo/ ii,jj
ii = 42
jj = ii / 2
print *, ii, jj
call sub
end program test
subroutine sub
integer aa, bb
common /foo/ aa,bb
print *, aa, bb
end subroutine sub
the current situation with DWARF is fairly satisfying (I set
breakpoints on each of the "print" lines):
Breakpoint 1, MAIN__ () at x.f90:7
7 print *, ii, jj
Current language: auto; currently fortran
(gdb) p ii
$1 = 42
(gdb) p jj
$2 = 21
(gdb) c
Continuing.
42 21
Breakpoint 2, sub_ () at x.f90:14
14 print *, aa, bb
(gdb) p aa
$3 = 42
(gdb) p bb
$4 = 21
(gdb) c
Continuing.
42 21
while for stabs+, it's not working at all:
Breakpoint 1, MAIN__ () at x.f90:7
7 print *, ii, jj
(gdb) p ii
Address of symbol "ii" is unknown.
(gdb) p jj
No symbol "jj" in current context.
(gdb) p aa
$1 = 0
(gdb) p bb
$2 = 1431662116
(gdb) c
Continuing.
42 21
Breakpoint 2, sub_ () at x.f90:14
14 print *, aa, bb
(gdb) p aa
$5 = 0
(gdb) p bb
$6 = 1431662116
(gdb) p ii
Address of symbol "ii" is unknown.
(gdb) p jj
No symbol "jj" in current context.
(gdb) c
Continuing.
42 21
With your patch added, it partly fixes stabs+ (partly only: see how
neither i nor a are displayed ok):
Breakpoint 1, MAIN__ () at x.f90:7
7 print *, ii, jj
(gdb) p ii
Address of symbol "ii" is unknown.
(gdb) p jj
$1 = 21
(gdb) p aa
$2 = 0
(gdb) p bb
$3 = 1431662116
(gdb) c
Continuing.
42 21
Breakpoint 2, sub_ () at x.f90:14
14 print *, aa, bb
(gdb) p ii
Address of symbol "ii" is unknown.
(gdb) p jj
No symbol "jj" in current context.
(gdb) p aa
$4 = 0
(gdb) p bb
$5 = 21
(gdb) c
Continuing.
42 21
But it breaks DWARF:
Breakpoint 1, MAIN__ () at x.f90:7
7 print *, ii, jj
Current language: auto; currently fortran
(gdb) p ii
No symbol "ii" in current context.
(gdb) p jj
No symbol "jj" in current context.
(gdb) p aa
$1 = 0
(gdb) p bb
$2 = 1431662116
(gdb) c
Continuing.
42 21
Breakpoint 2, sub_ () at x.f90:14
14 print *, aa, bb
(gdb) p aa
$3 = 0
(gdb) p bb
$4 = 1431662116
(gdb) p ii
No symbol "ii" in current context.
(gdb) p jj
No symbol "jj" in current context.
(gdb) c
Continuing.
42 21
So, while I agree that the current behaviour is not good for stabs and
not perfect for dwarf (because the scope of common variables is too
large, ie we can access aa and bb in the main program, where they
don't belong), I think it's more complicated than that. I'm fairly new
to this debug info issues (I started understanding dwarf, and haven't
yet done anything on stabs), so I'm not sure what is happening there,
but maybe you have an idea?
Regards,
FX