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* [Bug sim/18407] New: Bfin simulator - error in handling >>> (S), when shift value > 16
@ 2015-05-13 11:02 igorr at gitatechnologies dot com
  2015-05-13 11:06 ` [Bug sim/18407] " igorr at gitatechnologies dot com
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: igorr at gitatechnologies dot com @ 2015-05-13 11:02 UTC (permalink / raw)
  To: gdb-prs

https://sourceware.org/bugzilla/show_bug.cgi?id=18407

            Bug ID: 18407
           Summary: Bfin simulator - error in handling >>> (S), when shift
                    value > 16
           Product: gdb
           Version: 7.9
            Status: NEW
          Severity: normal
          Priority: P2
         Component: sim
          Assignee: unassigned at sourceware dot org
          Reporter: igorr at gitatechnologies dot com
                CC: vapier at gentoo dot org
  Target Milestone: ---

1. Let's compile the following code:
$ cat > test1.s
        .global __start
__start:
        LINK 0xc ;
        R1 = 2 ;
        R1 = R1 >>> 1;
        R1 = 2;
        R1 = R1 >> 1;
        R1 = 2;
        R1 = R1 >>> 1 (S);
        R1 = 2;
        .byte 0x82, 0xc6, 0xf9, 0x43 ;
        UNLINK;
        RTS;
$ bfin-linux-uclibc-gcc -nostdlib test1.s -o test1

2. Run objdump on it:
bfin-linux-uclibc-objdump -d test1

test1:     file format elf32-bfinfdpic

Disassembly of section .text:

00000074 <__start>:
  74:   00 e8 03 00     LINK 0xc;               /* (12) */
  78:   11 60           R1 = 0x2 (X);           /*              R1=0x2(  2) */
  7a:   82 c6 f9 03     R1 = R1 >>> 0x1;
  7e:   11 60           R1 = 0x2 (X);           /*              R1=0x2(  2) */
  80:   82 c6 f9 83     R1 = R1 >> 0x1;
  84:   11 60           R1 = 0x2 (X);           /*              R1=0x2(  2) */
  86:   82 c6 f9 43     R1 = R1 << 0x3f (S);
  8a:   11 60           R1 = 0x2 (X);           /*              R1=0x2(  2) */
  8c:   82 c6 f9 43     R1 = R1 << 0x3f (S);
  90:   01 e8 00 00     UNLINK;
  94:   10 00           RTS;

3. Bug/Feature (binutils?) R1 = R1 >>> 1(S) is displayed as R1 = R1 << 0x3f
(S);

4. Let's compile and run this code on VisualDSP++ environment simulator. 
in all 4 cases R1 will get the value 0x1 after the shift

5. Let's run the same test in bfin-simulator:
$ bfin-linux-uclibc-gdb test1
GNU gdb (GDB) 7.9
...<skip>
Reading symbols from test1...(no debugging symbols found)...done.
(gdb) b *0x74
Breakpoint 1 at 0x74
(gdb) set disassemble-next-line on
(gdb) target sim
Connected to the simulator.
(gdb) load
Loading section .text, size 0x24 lma 0x74
Start address 0x74
Transfer rate: 288 bits in <1 sec.
(gdb) r
Starting program: ./test1 

Breakpoint 1, 0x00000074 in _start ()
=> 0x00000074 <_start+0>:       00 e8 03 00     LINK 0xc;               /* (12)
*/
(gdb) display/x $r1
1: /x $r1 = 0x0
(gdb) si
0x00000078 in _start ()
=> 0x00000078 <_start+4>:       11 60   R1 = 0x2 (X);           /*             
R1=0x2(  2) */
1: /x $r1 = 0x0
(gdb) si
0x0000007a in _start ()
=> 0x0000007a <_start+6>:       82 c6 f9 03     R1 = R1 >>> 0x1;
1: /x $r1 = 0x2
(gdb) si
0x0000007e in _start ()
=> 0x0000007e <_start+10>:      11 60   R1 = 0x2 (X);           /*             
R1=0x2(  2) */
1: /x $r1 = 0x1
(gdb) si
0x00000080 in _start ()
=> 0x00000080 <_start+12>:      82 c6 f9 83     R1 = R1 >> 0x1;
1: /x $r1 = 0x2
(gdb) si
0x00000084 in _start ()
=> 0x00000084 <_start+16>:      11 60   R1 = 0x2 (X);           /*             
R1=0x2(  2) */
1: /x $r1 = 0x1
(gdb) si
0x00000086 in _start ()
=> 0x00000086 <_start+18>:      82 c6 f9 43     R1 = R1 << 0x3f (S);
1: /x $r1 = 0x2
(gdb) si
0x0000008a in _start ()
=> 0x0000008a <_start+22>:      11 60   R1 = 0x2 (X);           /*             
R1=0x2(  2) */
1: /x $r1 = 0x7fffffff
(gdb) 

6. Bug. After the last shift R1 should be equal to 0x1. Saturated shift Right
is treated as saturated shift left.

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^ permalink raw reply	[flat|nested] 7+ messages in thread
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Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-05-13 11:02 [Bug sim/18407] New: Bfin simulator - error in handling >>> (S), when shift value > 16 igorr at gitatechnologies dot com
2015-05-13 11:06 ` [Bug sim/18407] " igorr at gitatechnologies dot com
2015-05-13 11:12 ` igorr at gitatechnologies dot com
2015-05-13 16:02 ` vapier at gentoo dot org
2015-05-13 16:16 ` igorr at gitatechnologies dot com
2015-05-13 16:56 ` vapier at gentoo dot org
2015-10-11  7:43 ` cvs-commit at gcc dot gnu.org

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