as: M32R-Directives
9.20.2 M32R Directives
----------------------
The Renesas M32R version of 'as' has a few architecture specific
directives:
'low EXPRESSION'
The 'low' directive computes the value of its expression and places
the lower 16-bits of the result into the immediate-field of the
instruction. For example:
or3 r0, r0, #low(0x12345678) ; compute r0 = r0 | 0x5678
add3, r0, r0, #low(fred) ; compute r0 = r0 + low 16-bits of address of fred
'high EXPRESSION'
The 'high' directive computes the value of its expression and
places the upper 16-bits of the result into the immediate-field of
the instruction. For example:
seth r0, #high(0x12345678) ; compute r0 = 0x12340000
seth, r0, #high(fred) ; compute r0 = upper 16-bits of address of fred
'shigh EXPRESSION'
The 'shigh' directive is very similar to the 'high' directive. It
also computes the value of its expression and places the upper
16-bits of the result into the immediate-field of the instruction.
The difference is that 'shigh' also checks to see if the lower
16-bits could be interpreted as a signed number, and if so it
assumes that a borrow will occur from the upper-16 bits. To
compensate for this the 'shigh' directive pre-biases the upper 16
bit value by adding one to it. For example:
For example:
seth r0, #shigh(0x12345678) ; compute r0 = 0x12340000
seth r0, #shigh(0x00008000) ; compute r0 = 0x00010000
In the second example the lower 16-bits are 0x8000. If these are
treated as a signed value and sign extended to 32-bits then the
value becomes 0xffff8000. If this value is then added to
0x00010000 then the result is 0x00008000.
This behaviour is to allow for the different semantics of the 'or3'
and 'add3' instructions. The 'or3' instruction treats its 16-bit
immediate argument as unsigned whereas the 'add3' treats its 16-bit
immediate as a signed value. So for example:
seth r0, #shigh(0x00008000)
add3 r0, r0, #low(0x00008000)
Produces the correct result in r0, whereas:
seth r0, #shigh(0x00008000)
or3 r0, r0, #low(0x00008000)
Stores 0xffff8000 into r0.
Note - the 'shigh' directive does not know where in the assembly
source code the lower 16-bits of the value are going set, so it
cannot check to make sure that an 'or3' instruction is being used
rather than an 'add3' instruction. It is up to the programmer to
make sure that correct directives are used.
'.m32r'
The directive performs a similar thing as the _-m32r_ command line
option. It tells the assembler to only accept M32R instructions
from now on. An instructions from later M32R architectures are
refused.
'.m32rx'
The directive performs a similar thing as the _-m32rx_ command line
option. It tells the assembler to start accepting the extra
instructions in the M32RX ISA as well as the ordinary M32R ISA.
'.m32r2'
The directive performs a similar thing as the _-m32r2_ command line
option. It tells the assembler to start accepting the extra
instructions in the M32R2 ISA as well as the ordinary M32R ISA.
'.little'
The directive performs a similar thing as the _-little_ command
line option. It tells the assembler to start producing
little-endian code and data. This option should be used with care
as producing mixed-endian binary files is fraught with danger.
'.big'
The directive performs a similar thing as the _-big_ command line
option. It tells the assembler to start producing big-endian code
and data. This option should be used with care as producing
mixed-endian binary files is fraught with danger.
Info Catalog
as: M32R-Opts
as: M32R-Dependent
as: M32R-Warnings