While exploring an unrelated bug (32702) I rearranged the unix_stream structure
in libgfortran/io/unix.c as shown below. This results in a segfault with
streamio_3.f90. Valgrind reports and invalid write of 1. With further
experimentation I can add 1 to the pointer returned by fd_alloc_w_at and I can
get the fault to artificially go away and valgrind to report no errors.
However, this does not actually eliminate the problem.
I am still pursuing this. In the meantime, the problem does not manifest with
current trunk as far as I can tell and valgrind reports clean. I am submitting
this report to track that something is wrong here and I am trying to fix it.
Note that all that I am doing is moving the location of the buffer pointer.
This manifests the problem. If I stick a pad integer between buffer and
small_buffer within the structure, the problem no longer manifests. I suspect
we are trashing the buffer pointer.
Index: unix.c
===================================================================
--- unix.c (revision 126610)
+++ unix.c (working copy)
@@ -97,7 +97,6 @@ typedef struct
gfc_offset dirty_offset; /* Start of modified bytes in buffer */
gfc_offset file_length; /* Length of the file, -1 if not seekable. */
- char *buffer;
int len; /* Physical length of the current buffer */
int active; /* Length of valid bytes in the buffer */
@@ -108,6 +107,7 @@ typedef struct
int unbuffered; /* =1 if the stream is not buffered */
+ char *buffer;
char small_buffer[BUFFER_SIZE];
}
unix_stream;
--
Summary: Segfault on WRITE with modified unix_stream structure
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libfortran
AssignedTo: jvdelisle at gcc dot gnu dot org
ReportedBy: jvdelisle at gcc dot gnu dot org
GCC host triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32752
