gfortran segfault on continuation at end of program followed by two or more newlines

Bug #1720699 reported by Andrew Gaspar
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
gcc
Confirmed
Medium
gcc-5 (Ubuntu)
Undecided
Unassigned
gcc-6 (Ubuntu)
Undecided
Unassigned
gcc-7 (Ubuntu)
Undecided
Unassigned

Bug Description

If you end a FORTRAN program with the continuation character '&' followed by two newlines, gfortran SEGFAULTs when attempting to compile the program.

This issue has a very minimal repro:

file: test.f90
```
end program &

```

The two newlines at the end are significant. The problem does not repro with 1 or 0 newlines, though it does repro with more newlines. The problem also repros when any of the lines following the continuation contain a comment. The problem repros with both LF and CRLF line endings.

I believe this program should compile without error.

Putting a token anywhere after the continuation, even separated by 2 or more newlines, results in the expected error messages.

I'm running this on Windows Subsystem for Linux, though it's not likely that is causing this bug.

The SEGFAULT error encountered:
```
andre@ANDREW-DESKTOP:/mnt/c/Users/andre/Projects/scratch$ gfortran test.f90 -o hello
f951: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-5/README.Bugs> for instructions.
```

gfortran --version
```
andre@ANDREW-DESKTOP:/mnt/c/Users/andre/Projects/scratch$ gfortran --version
GNU Fortran (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
```

lsb_release -rd
```
andre@ANDREW-DESKTOP:/mnt/c/Users/andre/Projects/scratch$ lsb_release -rd
Description: Ubuntu 16.04.3 LTS
Release: 16.04
```

apt-cache policy gfortran
```
andre@ANDREW-DESKTOP:/mnt/c/Users/andre/Projects/scratch$ apt-cache policy gfortran
gfortran:
  Installed: 4:5.3.1-1ubuntu1
  Candidate: 4:5.3.1-1ubuntu1
  Version table:
 *** 4:5.3.1-1ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status
```

Revision history for this message
Matthias Klose (doko) wrote :

please recheck with 16.04 and 17.10.

Changed in gcc-5 (Ubuntu):
status: New → Incomplete
Revision history for this message
Andrew Gaspar (angasp) wrote :

Repros in 17.04 (Hyper-V VM). Looking into 17.10.

gfortran test.f90 -o hello
```
f951: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-6/README.Bugs> for instructions.
```

gfortran --version
```
GNU Fortran (Ubuntu 6.3.0-12ubuntu2) 6.3.0 20170406
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```

lsb_release -rd
```
Description: Ubuntu 17.04
Release: 17.04
```

apt-cache policy gfortran
```
gfortran:
  Installed: 4:6.3.0-2ubuntu1
  Candidate: 4:6.3.0-2ubuntu1
  Version table:
*** 4:6.3.0-2ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu zesty/main amd64 Packages
        100 /var/lib/dpkg/status
```

Revision history for this message
Andrew Gaspar (angasp) wrote :

I assumed you meant 17.04, anyway. The original bug was filed against 16.04.

Revision history for this message
Andrew Gaspar (angasp) wrote :

Also repros in 17.10 (Hyper-V VM). Additional warning in compilation now.

gfortran test.f90 -o hello
```
f951: Warning: No location in statement
f951: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-7/README.Bugs> for instructions.
```

gfortran --version
```
GNU Fortran (Ubuntu 7.2.0-7ubuntu1) 7.2.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```

lsb_release -rd
```
Description: Ubuntu Artful Aardvark (development branch)
Release: 17.10
```

apt-cache policy gfortran
```
gfortran:
  Installed: 4:7.2.0-1ubuntu1
  Candidate: 4:7.2.0-1ubuntu1
  Version table:
 *** 4:7.2.0-1ubuntu1 500
        500 http://archive.ubuntu.com/ubuntu artful/main amd64 Packages
        100 /var/lib/dpkg/status
```

Revision history for this message
In , Matthias Klose (doko) wrote :

seen on all active versions (test file ends with two newlines):

$ cat test.f90
end program &

$ /usr/lib/gcc-snapshot/bin/gfortran test.f90
f951: Warning: No location in statement
f951: internal compiler error: Segmentation fault
0x7f3381724fbf ???
        /build/glibc-hBZSf0/glibc-2.27/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0x7f3381711b16 __libc_start_main
        ../csu/libc-start.c:310
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.

Revision history for this message
In , Dominiq (dominiq) wrote :

Confirmed from 4.8 up to trunk (9.0). An instrumented compiler gives

f951: Warning: No location in statement
../../work/gcc/fortran/trans.c:1768:39: runtime error: member access within null pointer of type 'struct gfc_linebuf'
f951: internal compiler error: Segmentation fault: 11

Changed in gcc:
importance: Unknown → Medium
status: Unknown → Confirmed
Revision history for this message
In , Anlauf (anlauf) wrote :

(In reply to Dominique d'Humieres from comment #1)
> Confirmed from 4.8 up to trunk (9.0). An instrumented compiler gives
>
> f951: Warning: No location in statement
> ../../work/gcc/fortran/trans.c:1768:39: runtime error: member access within
> null pointer of type 'struct gfc_linebuf'
> f951: internal compiler error: Segmentation fault: 11

The warning in comment#0 would be restored by the patch:

Index: gcc/fortran/trans.c
===================================================================
--- gcc/fortran/trans.c (revision 267065)
+++ gcc/fortran/trans.c (working copy)
@@ -1765,8 +1765,11 @@
 void
 gfc_set_backend_locus (locus * loc)
 {
- gfc_current_backend_file = loc->lb->file;
- input_location = loc->lb->location;
+ if (loc->lb)
+ {
+ gfc_current_backend_file = loc->lb->file;
+ input_location = loc->lb->location;
+ }
 }

However, this papers over the issue that the locus is not properly set.

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