Skip to main content

IAR Embedded Workbench for Arm 9.70.x

Creating assembler source with CFI support

In this section:

The recommended way to create an assembler language routine that handles call frame information correctly is to start with an assembler language source file created by the compiler.

  1. Start with suitable C source code, for example:

    int F(int);
int cfiExample(int i)
{
  return i + F(i);
}

  2. Compile the C source code, and make sure to create a list file that contains call frame information—the CFI directives.

    Danger

    On the command line, use the option -lA.

    Caution

    In the IDE, choose Project>Options>C/C++ Compiler>List and make sure the suboption Include call frame information is selected.

    For the source code in this example, the list file in 32-bit mode looks like this.

            NAME Cfi

        RTMODEL "__SystemLibrary", "DLib"

        EXTERN F

            PUBLIC cfiExample
        
        CFI Names cfiNames0
        CFI StackFrame CFA R13 DATA
        CFI Resource R0:32, R1:32, R2:32, R3:32, R4:32, R5:32, R6:32, R7:32
        CFI Resource R8:32, R9:32, R10:32, R11:32, R12:32, R13:32, R14:32
        CFI EndNames cfiNames0
        
            CFI Common cfiCommon0 Using cfiNames0
        CFI CodeAlign 4
        CFI DataAlign 4
        CFI ReturnAddress R14 CODE
        CFI CFA R13+0
        CFI R0 Undefined
        CFI R1 Undefined
        CFI R2 Undefined
        CFI R3 Undefined
        CFI R4 SameValue
        CFI R5 SameValue
        CFI R6 SameValue
        CFI R7 SameValue
        CFI R8 SameValue
        CFI R9 SameValue
        CFI R10 SameValue
        CFI R11 SameValue
        CFI R12 Undefined
        CFI R14 SameValue
        CFI EndCommon cfiCommon0
        

            SECTION `.text`:CODE:NOROOT(2)
        CFI Block cfiBlock0 Using cfiCommon0
        CFI Function cfiExample
        ARM
    cfiExample:
        PUSH     {R4,LR}
        CFI R14 Frame(CFA, -4)
        CFI R4 Frame(CFA, -8)
        CFI CFA R13+8
        MOVS     R4,R0
        MOVS     R0,R4
        BL       F
        ADDS     R0,R0,R4
        POP      {R4,PC}          ;; return
        CFI EndBlock cfiBlock0

        END

    Note

    The header file Common.i contains the macros CFI_NAMES_BLOCK, CFI_COMMON_ARM, and CFI_COMMON_Thumb, which declare a typical names block and a typical common block. These two macros declare several resources, both concrete and virtual.