From: timsuth@... (Tim Sutherland)
Date: 2004-01-09T21:51:42+09:00
Subject: Re: mysql-ruby for ruby 1.8.1 on windows ...

In article <slrnbvsctp.66r.timsuth@europa.zone>, Tim Sutherland wrote:
[...]
>I've "fixed" the instructions, in the sense that they make sense to me,
>however the mysql.so library I build this way segfaults on me sometimes.
>(But a binary I built a while ago in a similar way doesn't seem to segfault,
>at least I can't reproduce it.)

NB: From memory the one I built a while ago was done by using the error
messages from the linker when trying to build mysql-ruby (things like
"undefined reference `mysql_close@4'") to generate a .def listing the symbol
names we want to export, and then using dlltool to create a libmysqlclient.a
using these, and then "make distclean" in mysql-ruby and rebuilding.

i.e. a process like

$ dlltool --dllname /c/mysql/lib/opt/libmySQL.dll --output-lib /c/mysql/lib/libmysqlclient.a --def /c/mysql/include/Libmysql.def
$ ruby extconf.rb --with-mysql-dir=/c/mysql
$ make 2>errors.txt
$ cat > make_def.rb
syms = []
ARGF.each_line { |line|
  match = line.scan(/undefined reference `([^']*)'/)
  syms << match[0][0] if match.size == 1
}
puts('EXPORTS')
puts(syms.uniq)
^D
$ ruby make_def.rb < errors.txt > symbols.def
$ dlltool --dllname /c/mysql/lib/opt/libmySQL.dll --output-lib /c/mysql/lib/libmysqlclient.a --def symbols.def -k
$ make distclean
$ ruby extconf.rb --with-mysql-dir=/c/mysql
$ make
$ make install

If someone could test this process and report back it would be good,
otherwise I may have time to try it on Monday afternoon or Tuesday.

This idea assumes that the libmySQL.dll functions use stdcall, but were
compiled with MSVC using a .def file which says not to use the @<n>
decorations. gcc on the other hand always expects @<n> when stdcall is
used. Hence it gets confused when it tries to look for functions like
mysql_close@4 which don't exist. (Only 'mysql_close' does.)

Idea: mysql/lib/mysqlclient.lib is clearly using stdcall (has @<n>
suffixes), perhaps we could use this rather than libmySQL.dll. I will check
this when I have access to Windows next week.

>The basic issue with building the mysql library is that in the Mysql
>distribution, mysql/lib/Readme says the dlls are compiled with __cdecl,
>while the mysql/include header files say that everything uses __stdcall.
>
>Possibly the Readme is wrong and they really are using __stdcall. This could
>explain the segfaults.
[...]

I disassembled libmySQL.dll and a lot of the time 'call' is followed by
adding a constant to %esp. This suggests it really is using cdecl.

Why would mysql.h say the functions are __stdcall and libmySQL.dll use
__cdecl?

Mini-rant: Microsoft - if you're going to have three different calling
conventions (cdecl, stdcall, fastcall), it would be good to have something
like:
	cdecl functions are prefixed with CDECL_
	stdcall functions are prefixed with STDCALL_
	fastcall function are prefixed with FASTCALL_

e.g.
	CDECL_mysql_close
or	STDCALL_mysql_close

so compilers could automatically detect the calling convention and Do The
Right Thing.