Hi all,
here is the biggest issue I am experiencing with my builds of the Apache
for NetWare using the GNU stuff:
5. CodeWarrior bitfields alignment (compatibility) issue
The Apache binaries produced by the CodeWarrior (currently the only one
officially supported tool for NetWare builds of the Apache server) are
affected by an alignment issue (bitfields). It causes incompatibility
between the core and external modules built with other tools (GNU stuff,
Watcom, ...).
There is a structure called "uri_components" defined in src/include/util_uri.h:
typedef struct {
// ...
unsigned short port;
unsigned is_initialized:1;
unsigned dns_looked_up:1;
unsigned dns_resolved:1;
} uri_components;
... and it is used within a structure called "request_rec" (widely used
by the modules and the core) defined in src/include/httpd.h:
struct request_rec {
//...
uri_components parsed_uri; /* components of uri, dismantled */
void *per_dir_config; /* Options set in config files, etc. */
void *request_config; /* Notes on *this* request */
//...
};*
*An "unsigned short port" element is incorrectly aligned to 4 bytes (should be 2
bytes) and the following set of bitfields is incorrectly aligned to 4 bytes (should by
1 byte) by CW compiler => the size of "uri_components" is different (+5 bytes than
usual, e.g. if compiling with gcc), offset to bitfield (the same for all its
components) also differ.
Most problems (abends) occur if accessing something below a "parsed_uri" structure
element (typically a "per_dir_config" used by a "ap_get_module_config" macro in some
modules).
For more understanding: Here is the latest posting from Guenter Knauf
taken from the "support.apachebuilds" forum on nntp.wiserlabz.com news
server, where this issue was discussed:
>>>>>
Hi all,
the following (unofficial) answer I received from Metrowerks support;
I hope that this is NOT the final word......
=========
Hi,
I just got this in, and it looks to be the final word I am going to get. So
why don't you look this over, (I've left it verbatim) and tell me if this is
acceptable to you. It looks just like and implementation dependent item
where you should not count on it working the same.
Ron
=========
I agree this is an undesirable way for bitfields to be aligned, but this
agrees with MSVC, upon which we based the bitfield layout. (In MSVC the
smallest we can make the struct is 4 bytes!)
I think the way to work around this is to change the bitfield base type to
"unsigned char". The type of the bitfield is used in determining how it is
aligned; thus, using a smaller type will require a smaller alignment.
P.S. Remind the developers that this style of bitfield alignment is neither
"correct" or "incorrect" (unless something really bad is happening such as
bitfields overlapping each other or other members of the struct) since
neither ANSI nor C99 define how compilers implement bitfields. This is
strictly the vendor's decision.
<<<<<
I suggest to fix the problem as described (patch attached), even if it will be
considered as CodeWarrior's bug (and fixed, then) by Metrowerks or not. I've
detailedly analyzed the issue and I see no way how to stay backwardly compatible with
this issue, so all binaries for NetWare platform (Apache core+modules from CVS sources
and all "3rd party" external modules produced with CW) should be re-built after the
fix (if it will be commited) - it will not be possible to mix new NLMs with older
Apache core or modules.
I have tested the fix with CW 5.3 and gcc 2.95.3 and it seems that alignment of
problematic structures is the same (it differs from current status quo, of course).
The change in the source file shared on all platforms is requested, so verification on
these ones will be needed. I don't expect problems (no change in alignment) on
platforms where the GNU stuff is used (gcc). Thanks.
Regards,
Pavel
--- util_uri.h.orig Mon Feb 26 16:49:32 2001
+++ util_uri.h Mon Aug 27 15:44:41 2001
@@ -106,10 +106,10 @@
unsigned short port; /* The port number, numeric, valid only if port_str !=
NULL */
- unsigned is_initialized:1;
+ unsigned char is_initialized:1;
- unsigned dns_looked_up:1;
- unsigned dns_resolved:1;
+ unsigned char dns_looked_up:1;
+ unsigned char dns_resolved:1;
} uri_components;
