Integer and Non-scalar Parameters

Article
06/30/2006

In most circumstances, the first four 32-bit words of integer or nonscalar arguments are passed in registers R4-R7. The remaining words are placed on the stack frame, starting at a displacement of 16 bytes from the stack pointer. Parameter passing is based on the SH-3 calling sequence specification. For more information about calling sequence specifications, see SH-3 Calling Sequence Specification, SH3-DSP Calling Sequence Specifications, and SH-4 Calling Sequence Specification. For a complete description of the SH-3 or SH-4 calling standard, see the Hitachi SH-3 Calling Standard or the Hitachi SH-4 Calling Standard.

The following example shows how to access parameters from registers and local argument stack space according to the calling standards.

__asm(
   "add     R4,R5         ; add first two numbers\n"
   "add     R5,R6         ; add third number\n"
   "add     R6,R7         ; add fourth number\n"
   "mov.l   @(16,SP), R0  ; retrieve fifth number\n"
   "add     R0,R7         ; add fifth number\n"
   "mov.l   @(20,SP), R0  ; get address of result\n"
   "mov.l   R7,@R0         ; save results"
   ,num1    // passed in R4
   ,num2    // passed in R5
   ,num3    // passed in R6
   ,1000    // passed in R7
   ,0xFFFF  // passed in stack at a displacement of 16 bytes from SP
   ,&result // passed in stack at a displacement of 20 bytes from SP
   );

For the preceding example, the compiler places num1 in R4, num2 in R5, num3 in R6, and 1000 in R7. The remaining arguments 0xffff and &result will be placed in the stack frame.

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Integer and Non-scalar Parameters

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