41.5. Opcodes

Computes the higher 16 bits of the given expression and stores it into the immediate operand field of the given instruction. For example:

mulhi hi0(here - there), r5, r6

computes the difference between the address of labels 'here' and 'there', takes the upper 16 bits of this difference, shifts it down 16 bits and then mutliplies it by the lower 16 bits in register 5, putting the result into register 6.

Computes the lower 16 bits of the given expression and stores it into the immediate operand field of the given instruction. For example:

addi lo(here - there), r5, r6

computes the difference between the address of labels 'here' and 'there', takes the lower 16 bits of this difference and adds it to register 5, putting the result into register 6.

Computes the higher 16 bits of the given expression and then adds the value of the most significant bit of the lower 16 bits of the expression and stores the result into the immediate operand field of the given instruction. For example the following code can be used to compute the address of the label 'here' and store it into register 6:

movhi hi(here), r0, r6 movea lo(here), r6, r6

The reason for this special behaviour is that movea performs a sign extension on its immediate operand. So for example if the address of 'here' was 0xFFFFFFFF then without the special behaviour of the hi() pseudo-op the movhi instruction would put 0xFFFF0000 into r6, then the movea instruction would takes its immediate operand, 0xFFFF, sign extend it to 32 bits, 0xFFFFFFFF, and then add it into r6 giving 0xFFFEFFFF which is wrong (the fifth nibble is E). With the hi() pseudo op adding in the top bit of the lo() pseudo op, the movhi instruction actually stores 0 into r6 (0xFFFF + 1 = 0x0000), so that the movea instruction stores 0xFFFFFFFF into r6 - the right value.

Computes the 32 bit value of the given expression and stores it into the immediate operand field of the given instruction (which must be a mov instruction). For example:

mov hilo(here), r6

computes the absolute address of label 'here' and puts the result into register 6.

Computes the offset of the named variable from the start of the Small Data Area (whoes address is held in register 4, the GP register) and stores the result as a 16 bit signed value in the immediate operand field of the given instruction. For example:

ld.w sdaoff(_a_variable)[gp],r6

loads the contents of the location pointed to by the label '_a_variable' into register 6, provided that the label is located somewhere within +/- 32K of the address held in the GP register. [Note the linker assumes that the GP register contains a fixed address set to the address of the label called '__gp'. This can either be set up automatically by the linker, or specifically set by using the -defsym __gp=<value> command line option].

Computes the offset of the named variable from the start of the Tiny Data Area (whoes address is held in register 30, the EP register) and stores the result as a 4,5, 7 or 8 bit unsigned value in the immediate operand field of the given instruction. For example:

sld.w tdaoff(_a_variable)[ep],r6

loads the contents of the location pointed to by the label '_a_variable' into register 6, provided that the label is located somewhere within +256 bytes of the address held in the EP register. [Note the linker assumes that the EP register contains a fixed address set to the address of the label called '__ep'. This can either be set up automatically by the linker, or specifically set by using the -defsym __ep=<value> command line option].

Computes the offset of the named variable from address 0 and stores the result as a 16 bit signed value in the immediate operand field of the given instruction. For example:

movea zdaoff(_a_variable),zero,r6

puts the address of the label '_a_variable' into register 6, assuming that the label is somewhere within the first 32K of memory. (Strictly speaking it also possible to access the last 32K of memory as well, as the offsets are signed).

Computes the offset of the named variable from the start of the Call Table Area (whoes address is helg in system register 20, the CTBP register) and stores the result a 6 or 16 bit unsigned value in the immediate field of then given instruction or piece of data. For example:

callt ctoff(table_func1)

will put the call the function whoes address is held in the call table at the location labeled 'table_func1'.

Indicates that the following sequence of instructions is a long call to function name. The linker will attempt to shorten this call sequence if name is within a 22bit offset of the call. Only valid if the -mrelax command line switch has been enabled.

Indicates that the following sequence of instructions is a long jump to label name. The linker will attempt to shorten this code sequence if name is within a 22bit offset of the jump. Only valid if the -mrelax command line switch has been enabled.