[fpc-devel] Arm Thumb2 - Stellaris status
David Welch
dwelch at dwelch.com
Sat Aug 20 22:24:34 CEST 2011
thumb2 is an extension to thumb not arm, you can mix thumb and arm in T
variants like the v4T v5T and anything after that v6 on up, except for
the cortex-m variants which are thumb+thumb2 only and cannot execute ARM
32 bit instructions (yes thumb2 32 bit thumb extensions but nothing from
the ARM instruction set).
Here is an example of the problem I am seeing:
took a clean copy from svn
svn co http://svn.freepascal.org/svn/fpc/trunk fpc
cd fpc
make clean buildbase installbase CROSSINSTALL=1 OS_TARGET=embedded
CPU_TARGET=arm INSTALL_PREFIX=/fpcarm
---- test.pp ----
procedure Wait(d : dword);
begin
while d<>0 do
dec(d);
end;
begin
while true do
begin
Wait($20000);
end;
end.
---- test.pp ----
./compiler/ppcrossarm -Parm -Tembedded -Wpstm32f103re -Cpcortexm3 test.pp
Free Pascal Compiler version 2.7.1 [2011/08/20] for arm
Copyright (c) 1993-2011 by Florian Klaempfl and others
Target OS: Embedded
Compiling test.pp
Assembling program
Linking test
/opt/embarm/arm-embedded-ld: warning: library search path
"/usr/local/lib/fpc/2.7.1/units/arm-embedded/rtl/" is unsafe for
cross-compilation
14 lines compiled, 0.0 sec
then dumped the binary:
08000000 <_START-0x158>:
8000000: 2000fffc strdcs pc, [r0], -ip
8000004: 08000405 stmdaeq r0, {r0, r2, sl}
8000008: 08000405 stmdaeq r0, {r0, r2, sl}
800000c: 08000405 stmdaeq r0, {r0, r2, sl}
8000010: 08000405 stmdaeq r0, {r0, r2, sl}
8000014: 08000405 stmdaeq r0, {r0, r2, sl}
8000018: 08000405 stmdaeq r0, {r0, r2, sl}
...
08000194 <PASCALMAIN>:
8000194: 46ec mov ip, sp
8000196: e92d 4800 stmdb sp!, {fp, lr}
800019a: f1ac 0b04 sub.w fp, ip, #4
800019e: b08a sub sp, #40 ; 0x28
80001a0: f000 f844 bl 800022c <FPC_INITIALIZEUNITS>
80001a4: e004 b.n 80001b0 <PASCALMAIN+0x1c>
80001a6: bf00 nop
80001a8: f44f 3000 mov.w r0, #131072 ; 0x20000
80001ac: f7ff ffd8 bl 8000160 <P$PROGRAM_WAIT$LONGWORD>
80001b0: e7fa b.n 80001a8 <PASCALMAIN+0x14>
80001b2: f000 f8ff bl 80003b4 <FPC_DO_EXIT>
80001b6: 46dd mov sp, fp
80001b8: b001 add sp, #4
80001ba: e91d 8800 ldmdb sp, {fp, pc}
80001be: bf00 nop
...
08000404 <STM32F103__FPC_START>:
8000404: e59f103c ldr r1, [pc, #60] ; 8000448 <STM32F103__FPC_START+0x44>
8000408: e59f203c ldr r2, [pc, #60] ; 800044c <STM32F103__FPC_START+0x48>
800040c: e59f303c ldr r3, [pc, #60] ; 8000450 <STM32F103__FPC_START+0x4c>
8000410: e1520003 cmp r2, r3
8000414: 94910004 ldrls r0, [r1], #4
First off 0x08000405 implies a thumb target but it is not thumb code, it
is arm code so 0x08000404 would be correct but that is still wrong
because cores with that vector table (cortex-m) cannot execute arm
instructions.
Looking at that first instruction in the reset handler
08000404 <STM32F103__FPC_START>:
8000404: e59f103c ldr r1, [pc, #60] ; 8000448 <STM32F103__FPC_START+0x44>
IPUBWL
1110 01011001 r15, r1, 0x03C
And that was properly decoded by objdump, immediate offset rn+offset12,
load, word sized, etc.
PC is 0x800040C at that time so load address is 0x800040C+0x03C = 0x8000448
You can tell both by 32 bit numbers in the dump but the dominance of an
0xE as the first nibble also implies these are arm instructions not
thumb (need to see a long chunk of code to see the pattern). Had they
been thumb instructions but decoded wrong by the disassembler then the
first and fourth nibbles would have been dominated by like 6's and 7's
or at least would stand out compared to the other
nibbles.
if we decode this as thumb/thumb2
0xE59F
//B(2) unconditional branch
if((inst&0xF800)==0xE000)
{
rb=(inst>>0)&0x7FF;
if(rb&(1<<10)) rb|=(~0)<<11;
rb<<=1;
rb+=pc;
rb+=2;
write_register(15,rb);
return(0);
}
1110010110011111
11100 10110011111
...11111110110011111
...111111101100111110
...11 1111 1011 0011 1110
pc = 0x405+4 = 0x409
pc + 0x...FFB3E =
0x409 - (0x4C1 + 1) = 0x7FFFF47
Unconditional branch to 0x07FFFF47 so it is a valid instruction, but
doesnt make much sense
This does though, the start code from stm32f103.pp
.globl _start
.text
_start:
// Copy initialized data to ram
ldr r1,.L_etext
ldr r2,.L_data
ldr r3,.L_edata
.Lcopyloop:
cmp r2,r3
ittt ls
ldrls r0,[r1],#4
strls r0,[r2],#4
bls .Lcopyloop
The instructions the assembler was able to encode it did:
8000404: e59f103c ldr r1, [pc, #60]
8000408: e59f203c ldr r2, [pc, #60]
800040c: e59f303c ldr r3, [pc, #60]
8000410: e1520003 cmp r2, r3
8000414: 94910004 ldrls r0, [r1], #4
....
8000448: 08000468 stmdaeq r0, {r3, r5, r6, sl}
800044c: 20000000 andcs r0, r0, r0
8000450: 20000048 andcs r0, r0, r8, asr
0x08000468 is the word aligned address for the end of the text segment
and 0x20000000 the beginning of text for this example so that is correct
as well.
and interestingly the ittt ls instruction is discarded.
The code from stm32f103.pp
ldr r1,.L_etext
ldr r2,.L_data
ldr r3,.L_edata
.Lcopyloop:
cmp r2,r3
ittt ls
ldrls r0,[r1],#4
strls r0,[r2],#4
bls .Lcopyloop
when assembled should look like this
00000000 <.text>:
0: 4904 ldr r1, [pc, #16] ; (14 <.text+0x14>)
2: 4a05 ldr r2, [pc, #20] ; (18 <.text+0x18>)
4: 4b05 ldr r3, [pc, #20] ; (1c <.text+0x1c>)
6: 429a cmp r2, r3
8: bf9e ittt ls
a: f851 0b04 ldrls.w r0, [r1], #4
e: f842 0b04 strls.w r0, [r2], #4
12: e7f8 bls.n 6 <.text+0x6>
14: 00000001 andeq r0, r0, r1
18: 00000002 andeq r0, r0, r2
1c: 00000003 andeq r0, r0, r3
with different addresses of course...when assembled for thumb.
So it doesnt look like that is happening
Pascal main is definitely thumb+thumb2.
08000194 <PASCALMAIN>:
8000194: 46ec mov ip, sp
8000196: e92d 4800 stmdb sp!, {fp, lr}
800019a: f1ac 0b04 sub.w fp, ip, #4
800019e: b08a sub sp, #40 ; 0x28
More info about my setup:
svn info
URL: http://svn.freepascal.org/svn/fpc/trunk
Repository Root: http://svn.freepascal.org/svn/fpc
Repository UUID: 3ad0048d-3df7-0310-abae-a5850022a9f2
Revision: 18278
Node Kind: directory
Schedule: normal
Last Changed Author: florian
Last Changed Rev: 18278
Last Changed Date: 2011-08-19 18:06:52 -0400 (Fri, 19 Aug 2011)
Ubuntu 10.4 or something like that 64 bit host.
Linux dwelch-desktop 2.6.32-33-generic #72-Ubuntu SMP Fri Jul 29
21:07:13 UTC 2011 x86_64 GNU/Linux
fpc is what you apt-get so probably a little behind but stable in the
eyes of ubuntu or debian.
fpc
Free Pascal Compiler version 2.4.0-2ubuntu1.10.04 [2011/06/17] for x86_64
Copyright (c) 1993-2009 by Florian Klaempfl
/usr/lib/fpc/2.4.0/ppcx64 [options] <inputfile> [options]
Put + after a boolean switch option to enable it, - to di
GNU assembler (Sourcery G++ Lite 2011.03-42) 2.20.51.20100809
Copyright 2010 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `arm-none-eabi'.
So what did I do wrong? and what is the unsafe thing about?
Thanks,
David
On 08/20/2011 11:23 AM, Jeppe Græsdal Johansen wrote:
> Den 20-08-2011 16:46, David Welch skrev:
>> I was hoping for thumb support but I now see that the choices are
>> limited to arm and thumb+thumb2 (without any separation between thumb
>> and thumb2). Actually thumb2 wasnt working for me, I got an arm+thumb2
>> mix, so I will ride this along for a while and see what comes up,
>> otherwise limit my use to ARM targets, or start working on a thumb
>> backend. Adding backends as well as arm embedded are of interest to me
>> so I may work on a little of both.
> Why thumb support? The choices are indeed currently only either ARM or
> Thumb2(which is Thumb+32 bit extensions). Thumb2 is a variable length
> instruction set that looks like an arm+thumb mix, so I guarantee you
> that it works :)
> _______________________________________________
> fpc-devel maillist - fpc-devel at lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-devel
> .
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