Hello,
I'm currently working with Contiki, on a platform that uses a
MSP430F1611 uC.
I'm using the git branch of mspgcc4, with gcc version 4.4.5 and libc
version ti_20101114.
Here are excerpts of the source code i'm trying to compile, preprocessed
using the -E option:
################
void *packetbuf_dataptr(void);
struct cxmac_hdr {
uint8_t dispatch;
uint8_t type;
};
struct cxmac_hdr *hdr;
hdr = packetbuf_dataptr();
if(hdr->dispatch == 0 && hdr->type == 0x13) {
[...]
}
################
The packetbuf_dataptr() function returns a pointer inside a byte array.
The index of the returned pointer depends of the length of the header of
a received packet.
So, even if the byte array that is used to store the packet is aligned
on an even address, the returned pointer can be an odd address if the
header length length is odd.
When compiling with -O0, everything's fine, as byte variants of the mov,
tst and cmp instructions are used:
################
601c: b0 12 a0 88 call #0x88a0
6020: 84 4f 1c 00 mov r15, 28(r4) ;0x001c(r4)
6024: 1f 44 1c 00 mov 28(r4), r15 ;0x001c(r4)
6028: 6f 4f mov.b @r15, r15
602a: 4f 93 tst.b r15
602c: 1b 20 jnz $+56 ;abs 0x6064
602e: 1f 44 1c 00 mov 28(r4), r15 ;0x001c(r4)
6032: 5f 4f 01 00 mov.b 1(r15), r15 ;0x0001(r15)
6036: 7f 90 13 00 cmp.b #19, r15 ;#0x0013
603a: 14 20 jnz $+42 ;abs 0x6064
################
But when compiling with -Os, the two tests inside the if condition are
merged into one single cmp instruction:
################
567c: b0 12 8a 6a call #0x6a8a
5680: bf 90 00 13 cmp #4864, 0(r15) ;#0x1300, 0x0000(r15)
5684: 00 00
5686: 0d 20 jnz $+28 ;abs 0x56a2
################
And in the event that r15 contains an odd address, its LSB is discarded,
and the comparison is done against wrong bytes of the array.
I believe this is a bug, but I'm not really familiar with gcc internals.
Should I fill in a bug report ? Do you need additional details ?
Is there an optimization option I could disable without too many side
effects (I still need the size optimization for the code to fit on the
uC)?
Best regards,
Alexandre Boeglin
------------------------------------------------------------------------------
Beautiful is writing same markup. Internet Explorer 9 supports
standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 & L3.
Spend less time writing and rewriting code and more time creating great
experiences on the web. Be a part of the beta today
http://p.sf.net/sfu/msIE9-sfdev2dev
_______________________________________________
Mspgcc-users mailing list
Mspgcc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/mspgcc-users
