Skip to main content

IAR Embedded Workbench for RISC-V 3.40

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 looks like this.

            EXTERN F

        PUBLIC cfiExample
        
          CFI Names cfiNames0
          CFI StackFrame CFA sp DATA
          CFI Resource ra:32, sp:32, gp:32, tp:32, t0:32, t1:32,
                       t2:32, s0:32
          CFI Resource s1:32, a0:32, a1:32, a2:32, a3:32, a4:32,
                       a5:32, a6:32
          CFI Resource a7:32, s2:32, s3:32, s4:32, s5:32, s6:32,
                       s7:32, s8:32
          CFI Resource s9:32, s10:32, s11:32, t3:32, t4:32,
                       t5:32, t6:32
          CFI VirtualResource ?RET:32
          CFI EndNames cfiNames0
              CFI Common cfiCommon0 Using cfiNames0
          CFI CodeAlign 1
          CFI DataAlign 1
          CFI ReturnAddress ?RET CODE
          CFI CFA sp+0
          CFI ra SameValue
          CFI gp SameValue
          CFI tp SameValue
          CFI t0 Undefined
          CFI t1 Undefined
          CFI t2 Undefined
          CFI s0 SameValue
          CFI s1 SameValue
          CFI a0 Undefined
          CFI a1 Undefined
          CFI a2 Undefined
          CFI a3 Undefined
          CFI a4 Undefined
          CFI a5 Undefined
          CFI a6 Undefined
          CFI a7 Undefined
          CFI s2 SameValue
          CFI s3 SameValue
          CFI s4 SameValue
          CFI s5 SameValue
          CFI s6 SameValue
          CFI s7 SameValue
          CFI s8 SameValue
          CFI s9 SameValue
          CFI s10 SameValue
          CFI s11 SameValue
          CFI t3 Undefined
          CFI t4 Undefined
          CFI t5 Undefined
          CFI t6 Undefined
          CFI ?RET ra
          CFI EndCommon cfiCommon0
            SECTION `.text`:CODE:REORDER:NOROOT(2)
          CFI Block cfiBlock0 Using cfiCommon0
          CFI Function cfiExample
        CODE
cfiExample:
        //              ‑‑‑‑‑‑‑‑‑‑ prologue ‑‑‑‑‑‑‑‑‑‑
        addi      sp, sp, -0x10
          CFI CFA sp+16
        sw        ra, 0xc(sp)
          CFI ?RET Frame(CFA, -4)
        sw        s0, 0x8(sp)
          CFI s0 Frame(CFA, -8)
        //              ‑‑‑‑‑‑‑‑‑‑   body   ‑‑‑‑‑‑‑‑‑‑
        mv        s0, a0
        
          CFI FunCall F
        call      F
        add       a0, s0, a0
        //              ‑‑‑‑‑‑‑‑‑‑ epilogue ‑‑‑‑‑‑‑‑‑‑
        lw        ra, 0xc(sp)
          CFI ?RET ra
        lw        s0, 0x8(sp)
          CFI s0 SameValue
        addi      sp, sp, 0x10
          CFI CFA sp+0
        ret
          CFI EndBlock cfiBlock0
            SECTION `.iar_vfe_header`:DATA:NOALLOC:NOROOT(2)
        SECTION_TYPE SHT_PROGBITS, 0
        DATA
        DC32 0

        END

    Note

    The header file iarCfi.m defines a names block, and provides the macro CfiCom that declares a typical common block. This macro declares several resources, both concrete and virtual.