Abstracted assembler
From ScienceZero
Most low level details can be found in ARM Architecture Reference Manual ARMv8.
Contents
Goals
- Let the compiler allocate registers
- Make it possible to use readable variable names in a safe way
- Add a thin level of abstraction that does not require a full compiler to generate good code
Open questions
- What is the default data size, 32 or 64 bit?
- Pros for 32-bit:
- ints are usually 32-bit in C and C++, even on 64-bit machines so may be more in line with developer expectations
- may yield faster code
- Pros for 64-bit:
- Address locations / pointers need to be 64-bit, so 64-bit int may make it easier / more logical to do address / pointer calculations
- Attempt to use a 32-bit int as a pointer should probably give a compiler error. With 64-bit ints, such errors may be more rare
- Pros for 32-bit:
- How to specify floating-point operations?
- Options:
- Number with . infers float
- myvar = 1.0
- .f forces float
- myvar.f = 1
- Number with . infers float
- Options:
- How to handle expressions involving float?
- Options:
- Handle like in C and C++, where any int that becomes involved in float calculation is "upgraded" to a float first and the result becomes float
- Options:
- Which instruction sets should be supported?
- Options:
- Any that the underlying assembler support. So, anything that appears to be instructions is just passed through to the assembler after name to register resolve
- Options:
- How to specify SIMD operations?
- Options:
- Use language support for assembly instruction pass through and use SIMD instructions directly
- Options:
- What is the simplest type system that will work?
Language features
bit slicing
index index
a = n.[10..2]
index lsb
a = n.[10..]
msb index
a = n.[..2]
index count
a = n.[10,2]
msb-index index
a = n.[-2..] strip the two most significant bits
index
bit = n.[index]
Common operators
Using python operator precedence with assembly style additions ( ) Custom order of operations, a = (a + b) * c Arithmetic + addition <+> addition and set condition codes on result - * / Comparisons = < > <= >= <> Bitwise logical Normal Alternative? & and | or ^ eor &~ bic |~ orn ^~ eon ~ not Shifts Normal High precedence << lsl >> lsr >>> asr >|> ror
Built in functions
clz count leading zeros cls count leading signs rbit mirror bits rev swap endian cnt population count max min swap adr returns the address of a label Conditional functions true false CSEL cond x y select x | y CSINC cond x y select increment x+1 | y CSINV cond x y select inversion ~x | y CSNEG cond x y select negation -x | y CINC cond x increment x+1 | x CINV cond x invert ~x | x CNEG cond x negate -x | x CSET cond set 1 | 0 CSETM cond set mask -1 | 0
Program flow
< reg-list = > label <reg-list>
Function call
return <reg-list>
Return from function with zero or more variables
again
Jump to the top of the loop
break
Jump to after the end of the loop
bcc
Conditional branch to a label
while cond
Execute the loop zero or more times while cond = true
dowhile cond
Execute the loop one or more times while cond = true
match
for x
for x = 1 to y
if then else
Conditional
<op> set condition flags on the result of op, a = b <+> c a = b > c ? 10 : 20 a = 10 if b > c else 20 a = if b > c then 10 else 20
<le> returns -1 if the condition flags matches the condition for Less than or equal otherwise 0. <c> returns the Carry flag as 0 or 1
.
Condition flags
N Negative - The most significant bit of the result, 1 if the result is negative otherwise 0. Z Zero - 1 if the result of the instruction is zero, 0 otherwise. C Carry - 1 if the instruction results in a carry condition, for example an unsigned overflow that is the result of an addition. V Overflow - 1 if the instruction results in an overflow condition, for example a signed overflow that is the result of an addition.
Mnemonic Condition Exactly opposite AL Always Any NOP CC Carry clear C=0 CS CS Carry set C=1 CC EQ Equal Z=1 NE GE Greater than or equal N=V LT GT Greater than N=V and Z=0 LE HI Higher (unsigned) C=1 and Z=0 LS LE Less than or equal N<>V or Z=1 GT LS Lower or same (unsigned) C=0 or Z=1 HI LT Less than N<>V GE MI Negative N=1 PL NE Not equal Z=0 EQ PL Positive N=0 MI VC Overflow clear V=0 VS VS Overflow set V=1 VC LO Lower (unsigned) Alias for CC HS HS Higher/same (unsigned) Alias for CS LO
Memory access
[adr].32 = 0
[adr].64 = {xpos,ypos} Multiple variables
b = [addr].s16
b = [addr1 + addr2].s16
arr[idx].64 = [addr2]
arr[idx]!64 = [addr2] Increment idx by 8
push {var-list} Access the system stack
pop {var-list}
Labels
Everything that starts on the first character on a line is a label. Labels are local to the function they are defined in. To reach other labels a fully qualified name is required.
label x = 3
notalabel
a = adr bootloader.var2 ; Fully qualified label name
Data structures
String Array BitArray List Hastable Set Tree
Memory manager
Implementation
Examples
Print value in hexadecimal
toHexStringNLZ: clz x11,x0 subs x11,x11,#64 sub x1,x1,x11,asr #2 cinc x1,x1,eq strb wzr,[x1] .loop: ubfx x10,x0,#0,#4 cmp x10,#9 add x10,x10,#'0' add x11,x10,#7 csel x11,x10,x11,ls strb w11,[x1,#-1]! lsr x0,x0,#4 cbne x0,.loop ret
tohhex adr number
leadingZeros = clz number
remainingBits = 64 - leadingZeros
remainingDigits = remainingBits / 4
adr = adr + remainingDigits
if remainingDigits = 0
adr += 1
[adr].8 = 0
dowhile number <> 0
digit = number.[3..0]
number = number >> 4
if digit <= 9
digit = digit + '0'
else
digit = digit + '0' + 7
adr -= 1
[adr].8 = digit
tohhex adr number
leadingZeros = clz number
remainingBits = 64 <-> leadingZeros
remainingDigits = remainingBits / 4
adr = adr + remainingDigits
adr = <eq> ? adr + 1 : adr
[adr].8 = 0
dowhile number <> 0
digit = number.[3..0]
number = number >> 4
if digit <= 9
digit = digit + '0'
else
digit = digit + '0' + 7
adr -= 1
[adr].8 = digit
Add with carry
x = y + z + <c>
