[Bug fortran/53993] New: gfortran ignores file part of #line directives

[Bug fortran/53993] New: gfortran ignores file part of #line directives

[mg1102 at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53993

             Bug #: 53993
           Summary: gfortran ignores file part of #line directives
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mg1102@web.de


Created attachment 27810
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27810
Example files to reproduce bug

#line directives inserted by source-code preprocessors are only partially
handled by gfortran. The line number part is OK, the file name part is ignored
and the input file name is used instead. This can mess up the debug information
of preprocessed Fortran files.

Example:
- The file 'dummy.f90' in the attached tar archive provides a simple Fortran
  code, calling a subroutine from the main program which prints "Hello world!".
  Compilation with gfortran 4.7.1 yields the following result:

  % gfortran -g -c dummy.f90
  % nm -l dummy.o
  000000000000006d t MAIN__    /tmp/bug/dummy.f90:1
                   U _gfortran_set_args    /tmp/bug/dummy.f90:3
                   U _gfortran_set_options    /tmp/bug/dummy.f90:3
                   U _gfortran_st_write    /tmp/bug/dummy.f90:6
                   U _gfortran_st_write_done    /tmp/bug/dummy.f90:6
                   U _gfortran_transfer_character_write    /tmp/bug/dummy.f90:6
  0000000000000000 T foo_    /tmp/bug/dummy.f90:5
  0000000000000078 T main    /tmp/bug/dummy.f90:3
  0000000000000020 r options.1.1854

- Suppose a source-code preprocessor inserts write statements to mark the
  begin and end of the main program as well as #line directives to account
  for modified line numbers and file name (prospective output provided as
  'dummy.mod.F90').

  % gfortran -g -c dummy.mod.F90
  % nm -l dummy.mod.o
  000000000000006d t MAIN__    /tmp/bug/dummy.mod.F90:1
                   U _gfortran_set_args    /tmp/bug/dummy.mod.F90:3
                   U _gfortran_set_options    /tmp/bug/dummy.mod.F90:3
                   U _gfortran_st_write    /tmp/bug/dummy.mod.F90:6
                   U _gfortran_st_write_done    /tmp/bug/dummy.mod.F90:6
                   U _gfortran_transfer_character_write   
/tmp/bug/dummy.mod.F90:6
  0000000000000000 T foo_    /tmp/bug/dummy.mod.F90:5
  000000000000013f T main    /tmp/bug/dummy.mod.F90:3
  0000000000000040 r options.3.1856

- As can be seen, the line number information provided by the #line directives
  is handled correctly, however, the file name refers to the actual input file
  instead of the file specified by the directive.

This bug seems to only affect Fortran, similar examples in C/C++ work fine.
This behavior has been verified with GCC 4.5.3, 4.6.2 and 4.7.1.

[Bug fortran/53993] gfortran ignores file part of #line directives for debugging

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53993

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |wrong-debug
   Last reconfirmed|                            |2012-07-17
                 CC|                            |burnus at gcc dot gnu.org
     Ever Confirmed|0                           |1
            Summary|gfortran ignores file part  |gfortran ignores file part
                   |of #line directives         |of #line directives for
                   |                            |debugging

--- Comment #1 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-07-17 11:55:40 UTC ---
Confirmed.

For diagnostic output, the file name is taken into account, but not for
generating debug info.

That the diagnostic part is okay, can be seen when making the test case
invalid, but also when looking at the code generated by
-fdump-tree-original-lineno (the correct file name is passed to the I/O
library).

In principle, it is handled via gcc/fortran/scanner.c's preprocessor_line().
The question is why it only works partially.

[Bug fortran/53993] gfortran ignores file part of #line directives for debugging

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53993

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-07-17 12:37:52 UTC ---
Okay, I think I understand:

  #include "myfile.f90"

gets translated (cpp) into

  # 1 "myfile.f90" 1
  ... content of that file ...
  # 8 "myfile.f90" 2

Where "1" is the first line of "file" and "8" is the line, in the main file,
after the #include.

However, '#line 1234 "file"' gets translated into a simple:
  # 1234 "file"

And the scanner.c code seemingly doesn't handle the case of having no number
after the string.


The following feels a bit hackish, but it works. I think the function could do
with some more comments.

--- a/gcc/fortran/scanner.c
+++ b/gcc/fortran/scanner.c
@@ -1728,2 +1728,8 @@ preprocessor_line (gfc_char_t *c)

+  if (! *c)
+    {
+      flag[1] = true;
+      goto process;
+    }
+
   for (;;)
@@ -1741,2 +1747,3 @@ preprocessor_line (gfc_char_t *c)

+process:
   /* Convert the filename in wide characters into a filename in narrow

[Bug fortran/53993] gfortran ignores file part of #line directives for debugging

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53993

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-07-17 15:52:54 UTC ---
Better documentation:
  http://gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html

Multiple flags are allowed - and mishandled is the case that no new file/return
flag is given.

[Bug fortran/53993] gfortran ignores file part of #line directives for debugging

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53993

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW

--- Comment #4 from Tobias Burnus <burnus at gcc dot gnu.org> 2012-07-18 09:28:51 UTC ---
Unfortunately, my attempts to generate a working patch failed, cf.
  http://gcc.gnu.org/ml/fortran/2012-07/msg00082.html
  http://gcc.gnu.org/ml/fortran/2012-07/msg00085.html

I always end up with warnings of the form   "filename left but not entered".
This warning is generated in scanner.c's preprocessor_line.

I think someone needs to understand what input can be expected. In particular:
How to handle the first few lines of the CPP output, of which only the last
seems to be relevant vs. those of #line directives, all of which have no flag.


For the last failing test case, the file (gfortran -E) starts with:

# 1 "libgfortran/generated/_abs_c4.F90"
# 1 "<command-line>"
# 1 "gcc-build/x86_64-unknown-linux-gnu/libgfortran//"
# 1 "libgfortran/generated/_abs_c4.F90"

Which is one line more than before.