WCC+NASM+WLINK: strange error addressing CONST data (wrong/even addressing)

[Algia71]

Hello
I'm porting a tiny experimental 80286 kernel from pure assembler (NASM) to assembler+C (NASM+OW). Boot sector code loads the BIN kernel at address 0x010000 and jumps to that address.

The kernel code, after segs/stack initialization, prints a message: when addressing the message (char*), sometimes the first char is skipped: the print function (puts) begins to print from the 2nd char onwards. Other times, everythng is OK: the string is printed starting from the 1st char.

Expected output:
Hello!

Actual output:
ello!

I discovered that the behaviour depends on the lenght in bytes of the code (text): when everything works, just adding a single (or uneven number of) nop instruction somewhere in the code (C or ASM doesn't matter) produces the wrong behaviour. And vice versa. [nop takes only one byte]

Inspecting the assembler code (with WDISM or NDISASM), it seems that WLINK resolves the address of the string message always rounding to even addresses.

I'm a very newbie with OW, so it's highly probable that I'm missing something in the linker parameters; or in the segment specifiers of ASM and C code. Any help will be welcome.

ASM startup code is:

start_:
    cli
    mov ax, 0x1000
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov sp, 0xFFFE
    mov bp, sp

    call main_

_halt:
    hlt
    jmp _halt

C code is:

void puts( char* s )
{
    while( *s )
        putc( *s++ );
}

void main( void )
{
    puts( "Hello!" );
}

Then I have a simple BIOS helper function:

global _putc
_putc:
    push bp
    mov bp, sp

    push ax
    push bx

    mov ah, 0x0E
    mov al, [bp+4]
    mov bh, 0
    mov bl, 0
    int 0x10

    pop bx
    pop ax

    pop bp
    ret

NASM command lines are:

nasm -f obj os/src/start.asm -o os/obj/start.obj
nasm -f obj os/src/bios.asm -o os/obj/bios.obj

OW command lines are:

wcc -d0 -wx -we -ecc -ei -zpw -2 -od -zl -zld -zls -s os/src/main.c -fo=os/obj/main.obj
wlink @os.lnk

os.lnk:

FILE os/obj/start.obj
FILE os/obj/main.obj
FILE os/obj/bios.obj
FORMAT RAW BIN
NAME os/bin/os.bin
OPTION NODEFAULTLIBS
OPTION START=start_
OPTION MAP=os/lst/os.map
OPTION VERBOSE

[Algia71]

I'm using OW 1.9 so I posted in the wrong place.

[jmalak]

It is general issue with linker.
Try to generate linker map file and check symbol addresses.
Also check segments alignment attribute because you mix segments from various tools.
Anyway you can use OW 2.0 linker with OW1.9 in case that it is bug in OW 1.9 linker.

[Algia71]

Thanks for the answer.

I discovered this post: it describes exactly my case. It seems that the linker bug was resolved in February 2019 in OW 2.0.

[Algia71]

For the sake of completeness: I recompiled and linked with Open Watcom 2.0 and it worked as expected.