Posted on May 17, 2011 at 12:42Hello !
I encountered to following problem with object code for STM32 generated by codesourcery toolchain arm-2008q1, while trying to compile given C file. Here it is its contents:
//strncpy.c
char *strncpy(char *pDest, const char *pSrc, size_t Num)
{ char *pS;
for (pS = pDest;0
*pS++ = *pSrc++; /* Kopiert maximal Num Zeichen von pSrc */
for (; 0
*pS++ = '\0';
return (pDest);
}
//End********************************************************************
Object code generated by codesourcery toolchain is:
080039fc :
80039fc: b500 push {lr}
80039fe: 4696 mov lr, r2
8003a00: b1aa cbz r2, 8003a2e
8003a02: 780b ldrb r3, [r1, #0]
8003a04: b90b cbnz r3, 8003a0a
8003a06: 4602 mov r2, r0
8003a08: e00a b.n 8003a20
8003a0a: 4602 mov r2, r0
8003a0c: 7013 strb r3, [r2, #0]
8003a0e: f11e 3eff adds.w lr, lr, #4294967295 ; 0xffffffff
8003a12: d00c beq.n 8003a2e 8003a14: f102 0201 add.w r2, r2, #1 ; 0x1
8003a18: f811 3f01 ldrb.w r3, [r1, #1]!
8003a1c: 2b00 cmp r3, #0
8003a1e: d1f5 bne.n 8003a0c
8003a20: f04f 0300 mov.w r3, #0 ; 0x0
8003a24: f802 3b01 strb.w r3, [r2], #1
8003a28: f11e 3eff adds.w lr, lr, #4294967295 ; 0xffffffff
8003a2c: d1f8 bne.n 8003a20 8003a2e: bd00 pop {pc}
//**********************************************************************
Used gcc options to compile are :
CFLAGS_DEFAULT = -c -pipe -mthumb -mcpu=cortex-m3 -Wcomment -Wimplicit
-Wreturn-type -Wunused -Wuninitialized
-ffunction-sections -fdata-sections -fomit-frame-pointer
-nostdinc -std=gnu89 -ffreestanding
//*************************************************************************
The problem i get in the code snippet above is fact, that link register(LR) is used as counter variable in loop implementation, which could be seen more precisely in these 2 instructions(marked with bold in in disassembly):
'' adds.w lr, lr, #4294967295 ; 0xffffffff
bne.n 8003a20
''
and
''
8003a0e: f11e 3eff adds.w lr, lr, #4294967295 ; 0xffffffff
8003a12: d00c beq.n 8003a2e
''
When I debug my application, LR value never reaches zero, so I get an hard fault exception(possibly when I reach out beyond onboard memory borders).
Although ''-mthumb -mcpu=cortex-m3'' is used, code generated for loop implementation is very strange to me. I 've looked through object code, generated for loop implementation, and I've never seen such a thing.
Is codesourcery toolchain is responsible for emitting ''uncorrect'' code or gcc options I used are responsible.
I hope somebody can tell me where I get wrong.
