Re: [arm-gnu] thumb code calling arm subroutine causes undefined insn exception

[Richard Earnshaw <rearnsha@xxxxxxx>]

On Wed, 2010-04-28 at 16:54 +0200, 42Bastian wrote:
> Am 28.04.2010 16:02, schrieb Andrew Kohlsmith (mailing lists account):
> > On Sunday 25 April 2010 10:43:51 pm Mark Mitchell wrote:
> >> Andrew Kohlsmith (mailing lists account) wrote:
> >>> Since I am already using -mcpu=arm7tdmi, would this indicate that there
> >>> is a bug in the compiler wherein it is assuming that the BLX instruction
> >>> exists on the ARM7TDMI/TDMI-S?
> >>
> >> Please post your exact options for all of (a) code compiled with
> >> GCC/G++, (b) code assembled with GAS, (c) link line.
> >
> > Actually some further inspection seems to lead to the conclusion that
> > incorrect bootup code (in my case it's using msr in thumb mode) causes the
> > linker to become confused.
> >
> > -A.
> >
> > boot.s:
> > ------------------
> > .equ MIN_STACK,         0x0004          /* enough for a RET */
> > .equ IRQ_STACK_LEN,     0x0080          /* 128 words */
> > .equ STACK_LEN,         0x0200          /* 512 words */
> >
> > /* .text is used instead of .section .text so it works with arm-aout too. */
> >
> >         .text
> >         .code 32
> >
> >         .align  0
> >
> >         .extern main
> >         .global start
> >         .global endless_loop
> >
> > start:
> >         ldr r0, =thumb_start + 1                /* +1 to set LSB to
> identify
> > destination as thumb code */
> >         bx r0
> 
> >
> >         .code 16
> 
> You should add
> 	.thumb_func
> and then omit the above +1
> 
> >
> > thumb_start:
> 

.thumb_func shouldn't be needed these days.

However, you probably want to add a 
	.type thumb_start, %function 
directive.

R.