arm7t and the BL thumb instruction?

arm7t and the BL thumb instruction?

[Brandon Warhurst]

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Here is the problem I'm having:  As I step through ARM code I successfully switch from ARM mode to Thumb mode.  However, my first instruction is a BL <someaddress> instruction.  I have stepped through SID watching this instruction execute.  Everything appears fine except that just as I should be executing the instruction, I look at the structure which contains the offset that the BL instruction contained and everything appears to be zero.  This leads to the instruction which executes the branch, however, it just branches to the next instruction, which is obviously wrong unless someaddress points to the next instruction (which it does not in my case).

Here's the question:  Is the BL instruction fully implemented?

bpw.

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Re: arm7t and the BL thumb instruction?

[Frank Ch. Eigler]

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Hi -

On Mon, May 05, 2003 at 10:56:20AM -0400, Brandon Warhurst wrote:
> Here is the problem I'm having:  As I step through ARM code I successfully
> switch from ARM mode to Thumb mode.  However, my first instruction is a
> BL <someaddress> instruction.  I have stepped through SID watching this
> instruction execute.  [...]

Using the "--trace-extract" may tell you almost as much as
stepping through it.

> Here's the question:  Is the BL instruction fully implemented?

In Arm mode, I see a BL instruction, but not one in Thumb mode.
In the latter, a branch-with-link is expressed as consecutive
"bl-hi" and "bl-lo" instructions.

What does "objdump -dr" say on the arm/thumb elf file?

- FChE

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Re: arm7t and the BL thumb instruction?

[Frank Ch. Eigler]

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Hi -

> sid.conf:42: component type sid-control-tksm unknown
> sid.conf:50: component type bridge-tcl unknown
> sid.conf:90: component tksm not found
> sid.conf:94: component tksm not found
> sid.conf:110: component tcl-event-consumer not found
> sid.conf:111: component tcl-event-consumer not found
> sid.conf:112: component tcl-event-consumer not found
> Configuration error.  Aborting.
> 
> Can you tell me what might be going on here?  the Tk/Tcl stuff compiled.
> The library is there.. Is there some environment variable I need to set?

If you are running an installed sid out of the directory given at
configure-time (using --prefix), you should not need to set any
environment variables.  Otherwise, you may need a variety -
TCL_PACKAGE_PATH, SID_EXEC_PREFIX.


- FChE

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Re: arm7t and the BL thumb instruction?

[Frank Ch. Eigler]

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Hi -

> [...] I think I might have located the problem, but am not sure.  If
> I read the code correctly, the Thumb decoder always makes
> entire_insn = base_insn >> 16 ... and if you are
> expecting the next instruction to appear in the upper end of base_insn this
> might make sense.  But if it for some reason appeared in the lower end of
> base_insn, you would throw away the instruction before anything got a chance
> to be executed.  [...]

Yikes.  I guess the thumb part hasn't been tested after it was last
regenerated.  I can fix this, though don't have any arm+thumb
elf binaries handy - do you?

- FChE

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