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Message
From: rachel_cy at hotmail.com<rachel_cy@h...>
Date: Thu Mar 20 20:06:38 CET 2008
Subject: [openrisc] Dead Loop in Generated Image of OR1200
I came across a problem of the generated image with the toolchain built
by the package
of drp-0.6.
Version information of the tools is
gcc 4.2.1
binutils: 2.17-1
uClibc 0.9.28.3
The small C program is attached at the bottom of this message.
I used the compiler of or32-elf-gcc and the command I used to
generated the image is
% or32-elf-gcc -s x.c -o x1
Here are the first few lines of the assembly code:
1 80000000: 18 20 03 00 l.movhi r1,0x300
2 80000004: a8 21 00 00 l.ori r1,r1,0x0
3 80000008: 9c 40 ff f9 l.addi r2,r0,0xfffffff9
4 8000000c: e0 21 10 03 l.and r1,r1,r2
5 80000010: 1b 80 00 01 l.movhi r28,0x1
6 80000014: ab 9c 2f 94 l.ori r28,r28,0x2f94
7 80000018: 1b c0 00 01 l.movhi r30,0x1
8 8000001c: ab de 2f e0 l.ori r30,r30,0x2fe0
9 80000020: d4 1c 00 00 l.sw 0x0(r28),r0
10 80000024: e4 9c f0 00 l.sfltu r28,r30
11 80000028: 13 ff ff fe l.bf 0x80000020
12 8000002c: 9f 9c 00 04 l.addi r28,r28,0x4
13 80000030: 18 60 90 00 l.movhi r3,0x9000
...
... The remaining lines of the assembly code are omitted.
...
The problem of the generated image is
At steps 5 and 6, register r28 is assigned a value of 0x12f94 and
at steps 7 and 8, register r30 is assigned a value of 0x12fe0. And up
to step 11, these values in register r28 and r30 do not change.
Step 10, the instruction l.sfltu compares [r28] to [r30], which should
set the flag bit,
since 0x12f94(r28) is less than 0x12fe0(r30). So the immedately
following instruction l.bf
directs the CPU to PC address 0x80000020, which is step 9. The
instruction at 0x80000020 is
l.sw, which just stores the data addressed by r28 with 0. When step 10
compares [r28] to
[r30] again, and step 11 turns to CPU to step 9 again.
Thus, steps 9, 10 and 11 effectively form a dead loop.
I am looking into the code of insn-output.c, insn-emit.c, emit-rtl.c,
optab.s, etc. But if someone
who is familiar with OR1200 port of GCC would help or point me to which
code I should look, that will be great.
Thank you.
Mark
====================
Attachment:
//------------- x.c ------------------------
1 int main()
2 {
3 int a, b, c, *p = (int *)(0x3fff0);
4
5 a = 0x55;
6 b = 0x88;
7
8 c = a + b;
9
10 *p = c;
11
12 return 0;
13 }
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