[Mingw-notify] [ mingw-Bugs-711086 ] Linking 16-bit code is broken

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Bugs item #711086, was opened at 2003-03-27 22:55
Message generated for change (Comment added) made by disasm
You can respond by visiting: 
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Brian Palmer (disasm)
Assigned to: Nobody/Anonymous (nobody)
Summary: Linking 16-bit code is broken

Initial Comment:
I am writing a boot manager named FreeLoader. Since it 
is a boot manager I have to write some 16-bit code to 
init protected mode so Mingw32 compiled code can run. I 
link it to an executable .exe file and the run "objcopy -O 
binary" to generate the flat binary file. This works great 
under all versions of gcc that I have tested (DJGPP, Linux 
gcc) except for Mingw32. The problem is that it seems to 
be fixing up the 16-bit addresses incorrectly. For 
example, in the latest FreeLoader code from cvs I have a 
16-bit function called switch_to_prot(). In the map file it 
lists this function (correctly) as 0x832f. In the resulting 
binary file (after the objcopy) when I step through it with 
bochs it is actually calling 0x832d, which is the wrong 
address.


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>Comment By: Brian Palmer (disasm)
Date: 2003-04-29 17:16

Message:
Logged In: YES 
user_id=64619

I have tried to recreate this bug using just one assembly 
source file, but I cannot do it. So I am sending you the 
FreeLoader source tree. The only program you need to compile 
FreeLoader besides MinGW is nasm. As long as you have nasm.
exe in your path everything should compile fine. To compile it 
all you need to do is change to the freeldr\freeldr directory 
and run make. All output is placed in freeldr\freeldr\obj\i386. 
freeldr.sys is the name of the binary boot file for FreeLoader.

Program versions:
E:\>make -v
GNU Make version 3.79.1
Built for mingw32
E:\>gcc -v
Reading specs from e:/mingw32/bin/../lib/gcc-lib/mingw32/3.
2/specs
Configured with: ../gcc/configure --with-gcc --with-gnu-ld 
--with-gnu-as --host=
mingw32 --target=mingw32 --prefix=/mingw --enable-threads 
--disable-nls --enable
-languages=f77,c++,objc,ada --disable-win32-registry 
--disable-shared
Thread model: win32
gcc version 3.2 (mingw special 20020817-1)
E:\>ld -v
GNU ld version 2.13.90 20021005
E:\>objcopy -V
GNU objcopy 2.13.90 20021005


More info on the bug:

It is actually linking everything up correctly most of the time. I 
call the switch_to_prot function from many places and I have 
only found one place that has generated the wrong address. If 
you look in freeldr\freeldr\arch\i386\int386.S line 140 you will 
see a call to switch_to_prot. In the map file switch_to_prot is 
at address 0x822f and the generated code for int386.S line 
140 is calling address 0x822d. In the binary freeldr.sys file the 
3 bytes for the instruction at line 140 in int386.S are at offset 
0x6646.

Let me know if you need any more information. My email 
address is br...@sg....

Brian

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Comment By: Danny Smith (dannysmith)
Date: 2003-03-27 23:38

Message:
Logged In: YES 
user_id=11494

What is version of objcopy? 

Please provide self-contained testcase that shows the 
bug. 

Danny

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