This is the mail archive of the
gdb-prs@sources.redhat.com
mailing list for the GDB project.
sim/1282: Thumb add pc,rn should not word align pc
- From: dmcq at tao-group dot com
- To: gdb-gnats at sources dot redhat dot com
- Date: 14 Jul 2003 12:03:03 -0000
- Subject: sim/1282: Thumb add pc,rn should not word align pc
- Reply-to: dmcq at tao-group dot com
>Number: 1282
>Category: sim
>Synopsis: Thumb add pc,rn should not word align pc
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: change-request
>Submitter-Id: net
>Arrival-Date: Mon Jul 14 12:08:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: dmcq@tao-group.com
>Release: GDB-5.3
>Organization:
>Environment:
I'm running the ARM simulator in my own environment and don't actually use GDB or any *nix.
>Description:
The Thumb 'add pc,rn' instruction should I believe jump to the address of the add op+4+contents of rn. However the simulator rounds the result down to a word boundary. I've tested on an ARM7 processor and it gave me my expected results.
The instruction was used to avoid having fixups or affecting r14 in a long branch.
>How-To-Repeat:
If you could run this thumb subroutine somehow:
.align 4
mov r0,#2
add r15, r0
add r0,#2
add r0, #2
add r0, #2
add r0, #2
mov r15, r14
it should return 6 and not 8.
>Fix:
I've found this using the latest versions in
src/sim/arm
The logical place for a fix is
thumbemu.c 1.5
in the code for 'Format 5' ADD, but it would be out of step with how that's written.
I've attached a proposed fix in diff.txt where the arm2 directory holds the new code for
armemu.c 1.30
armemu.h 1.15
where I instead change the code to only do the rounding down in those thumb operation equivalents that should round down, i.e. ADD rn,pc,#imm and LDR rn,[pc,#imm] - so it is a bit less certain of just affecting what should be affected than doing something in thumbemu.c.
>Release-Note:
>Audit-Trail:
>Unformatted: