ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Coding Practices
5.58 Identification of software floating-point division-by-zero errors
The C library helper function _fp_trapveneer() is called whenever an exception occurs. On
entry into this function, the state of the registers is unchanged from when the exception
occurred. Therefore, to find the address of the function in the application code that contains the
arithmetic operation that resulted in the exception, a breakpoint can be placed on the function
_fp_trapveneer() and LR can be inspected.
For example, suppose the C code of Example 5-7 is compiled from the command line using the
string:
armcc --fpmode ieee_full
When the assembly language code produced by the compiler is disassembled, the debugger
produces the output shown in Example 5-8.
Example 5-7 Trapped division-by-zero error
#include
#include
int main(void)
{ float a, b, c;
// Trap the Invalid Operation exception and untrap all other exceptions:
__ieee_status(FE_IEEE_MASK_ALL_EXCEPT, FE_IEEE_MASK_DIVBYZERO);
c = 0;
a = b / c;
printf("b / c = %f, ", a); // trap division-by-zero error
return 0;
}
Example 5-8 Disassembly of division by zero error
main:
00008080 E92D4010 PUSH {r4,lr}
00008084 E3A01C02 MOV r1,#0x200
00008088 E3A00C9F MOV r0,#0x9f00
0000808C EB000F1A BL __ieee_status
00008090 E59F0020 LDR r0,0x80b8
00008094 E3A01000 MOV r1,#0
00008098 EB000DEA BL _fdiv
0000809C EB000DBD BL _f2d
000080A0 E1A02000 MOV r2,r0
000080A4 E1A03001 MOV r3,r1
000080A8 E28F000C ADR r0,{pc}+0x14 ; 0x80bc
000080AC EB000006 BL __0printf
000080B0 E3A00000 MOV r0,#0
000080B4 E8BD8010 POP {r4,pc}
000080B8 40A00000 0x00 0x00 0xA0 '@'
000080BC 202F2062 'b' ' ' '/' ' '
000080C0 203D2063 'c' ' ' '=' ' '
000080C4 202C6625 '%' 'f' ',' ' '
000080C8 00000000 0x00 0x00 0x00 0x00
Placing a breakpoint on _fp_trapveneer and executing the disassembly in the debug monitor
produces:
ARM DUI 0375C Copyright © 2007-2008, 2011 ARM. All rights reserved. 5-74
ID061811
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