Re: [68332ABB] Odd and Odder

[brynn at tiny dot net]

Mark Palmerino wrote:
[snip]


It looks like the compiler is trying to pack the constants on byte boundarys.
there is a switch that you can tell it to align things on word boundarys, 
you might try that.

As to why that breaks it,  I would guess there is some CPUtype=M68K  define
that is missing, and packing constants on word boundarys would result if it
were in there.  Just a guess.


> If the referenced string is an odd number of characters, the program does
> *not* bomb.  For example, the following works:
> 
> lcd_print("123");
> 
> And the following does not work:
> 
> lcd_print("12");
> 
> The following works:
> 
> lcd_print("12\0");  //That's a backslash-zero for a Null, is interpreted as
> 1 char
> 
> And the following does not work:
> 
> lcd_print("123\0");
> 
> I'm guessing this gives credence to this being an 'alignment' problem.
> Unfortunately, I don't know what to do about it.
> 
> Here is a simple test c program:
> 
> #include <string.h>
> #include <stdio.h>
> 
> int main(void) {
>       int i;
>       char someText[256];
> 
>       strcpy(someText,"12");
> }
> 
> and here is the assembly that is produced by m68k-elf-gcc -S test.c
> 
>       .file   "alcdtest.c"
> gcc2_compiled.:
> .globl __main
> .section        .rodata
> .LC0:
>       .string "12"
> .text
> .globl main
>       .type    main,@function
> main:
>       link.w %a6,#-260
>       jsr __main
>       pea .LC0
>       move.l %a6,%d0
>       add.l #-260,%d0
>       move.l %d0,-(%sp)
>       jsr strcpy
>       addq.l #8,%sp
> .L2:
>       unlk %a6
>       rts
> .Lfe1:
>       .size    main,.Lfe1-main
>       .ident  "GCC: (GNU) 2.95.2 19991024 (release)"
> 
> When compiled and downloaded, this program bombs with the following output
> from cpu32bug:
> 
> Exception: Address Error
> Format/Vector=C00C
> SSW=00D6  Fault Addr.=00090CB9  Data=00007FEC  Cur. PC=00090120  Cnt.
> Reg.=0001
> PC   =00090126 SR   =2704=TR:OFF_S_7_..Z..   VBR  =00000000
> SFC  =5=SD     DFC  =5=SD     USP  =0000FC00 SSP* =00007FD4
> D0   =00000000 D1   =01D6FFFF D2   =00000000 D3   =00000000
> D4   =00000000 D5   =00000000 D6   =00000000 D7   =00000000
> A0   =0000315E A1   =00003156 A2   =0000315A A3   =00000000
> A4   =00000000 A5   =00000000 A6   =00007FF8 A7   =00007FD4
> 00090126 48780000           PEA.L       ($0).W
> 
> Now, if I change the string from "12" to "123", the program does not bomb.
> 
> I tried compiling with -fno-writable-strings and this made no difference.
> Also, if I do the following with char const, the program bombs:
> 
> char const footext[] = "12";
> .
> .
> .
> strcpy(someText,footext);
> 
> However, building the string up in the following manner, does work
> regardless of the number of characters that end up in the string:
> 
> int main(void) {
>       int i;
>       char someText[256];
>       char footext[256];
> 
> footext[0] = '1';
> footext[1] = '2';
> footext[2] = '3';
> footext[3] = '4';
> footext[4] = '\0';
> 
>       strcpy(someText,footext);
> }
> 
> So, with this new information, does anyone have any ideas for how to fix the
> problem?
> 
> Again, many, many thanks!
> 
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> 
> 
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