Re: arm-elf-as truncates branch offsets w/o warning

[Grant Edwards <grante at visi dot com>]

> ------------------------------testit2.s------------------------------
>      .text
>      .org 0x05000000
>      b    label1
>      nop
>      nop
>      nop
> label1:
>      nop
> --------------------------------------------------------------------

It doesn't appear to be possible to link an object file
produced by assembling the above case (final link failed:
Memory exhausted), so it's probably a moot question whether the
file contains incorrect object code or not.  ;)

However, the other case (non-reloc dest < 0x0400,0000 with
offset too large for the branch instruction) can be linked:

------------------------------testit.s------------------------------
        .text
        .org    0x0020

        b       label1

        .org    0x02001000
label1:
        nop
--------------------------------------------------------------------

The ARM branch instruction can only handle offsets of
-0x2000000 to +0x1ffffff, so the above jump isn't legal, but it
assembles and produces bad code:

$ arm-elf-as -o testit.o testit.s

**** this should have generated an error ****

$ arm-elf-objdump --source testit.o  

testit.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <label1-0x2001000>:
        ...
      20:       ea8003fe        b       fe001020 <label1+0xfc000020>
        ...

02001000 <label1>:
 2001000:       e1a00000        nop                     (mov r0,r0)
 
 
 
$ arm-elf-ld -o testit testit.o 
arm-elf-ld: warning: cannot find entry symbol _start; defaulting to 00008000

$ arm-elf-objdump --source testit  

testit:     file format elf32-littlearm

Disassembly of section .text:

00008000 <label1-0x2001000>:
        ...
    8020:       ea8003f6        b       fe009000 <__bss_end__+0xfbfffefc>
        ...

02009000 <label1>:
 2009000:       e1a00000        nop                     (mov r0,r0)


-- 
Grant Edwards
grante@visi.com