Convert Linux ARM Assembly Code for iOS
While getting OCaml 4.00.0 working on iOS a couple of years ago, I learned quite a lot about the differences between the Linux ARM assembler and the iOS ARM assembler. This information was hard-won: documentation for the iOS assembler seems rare to nonexistent (email me if you know where to find it). So I spent many hours reading the source code of as(1) at Apple’s open source site.
To capture what I found out and to apply it consistently, I wrote a Python script that converts ARM assembly code from the Linux format to the required iOS format. It contains all the wisdom I’ve accumulated so far.
Recently I’ve begun working with OCaml 4.01.0 on iOS, and I’ve found that the script holds up extremely well. In fact, so far no changes have been required; the script seems to be working just as well with the current toolchain as it did with the old one a couple of years ago!
I’m publishing here the latest version of the script, which I call arm-as-to-ios. I wrote the script specifically to convert the hand-written ARM assembly files of the OCaml runtime to work on iOS; however it does some conversions that aren’t required for the OCaml-on-iOS project.
I hope the script might help other people who need to port ARM assembly code from Linux to iOS. Granted, there probably aren’t a lot of people doing this. But if you are, maybe the script will be a useful starting point or at least a careful list of differences between the assemblers.
Keep in mind that the script can’t translate all possible assembly files. It makes many heuristic assumptions that work for me, and will probably be pretty close in many cases. If you have a specific set of assembly files to translate, you can probably adapt the script to work for you (but, no guarantees). To make a universal tool would take far more time than I can spend right now.
The output of the script is upward compatible. By this I mean that a converted assembly file works in its originally supported Linux environments as well as in iOS. This means that the converted assembly files can in theory be sent “upstream” to maintainers (if they’re comfortable with supporting iOS and/or the extra complexity of the code).
The current version of arm-as-to-ios is 1.4.0. In its current form, it does the following conversions:
Declare the ARM architecture for iOS with a
.machinepseudo-op. The possibilities arearmv6andarmv7.Specify that
armv7code should use the more space-efficient Thumb encoding in iOS.Generate declarations for functions, similar to the
.typepseudo-op for Linux assemblers. It appears that Apple requires.thumb_funcdeclarations only for Thumb functions. Other symbols are apparently assumed to be ARM functions. To make this work upward-compatibly, I define an assembly macro named.funtypethat is expanded properly in the different environments.Make sure that global symbols have the right format. For Linux, they look like “
abc”. For iOS, they look like “_abc” (with a leading underscore). To support upward compatibility, this is handled by a cpp macro namedGlo()that generates the proper symbol form for each environment.Make sure that assembler-local symbols have the right format. For Linux assemblers, they look like “
.Lxxx”. For the iOS assembler, they look like “Lxxx”. To support upward compatibly, this is handled by a cpp macro namedLoc()that generates the proper symbol form for each environment.Replace uses of
=value notation by explicit loads from memory. The Linux ARM assemblers interpretldr rM, =value to mean that the value should be loaded into register M immediately (usingmov) if possible, and loaded from memory (usingldrwith PC-relative addressing) otherwise. The Apple assembler seems not to support this, soarm-as-to-iosreplaces uses of=value with explicit memory loads, emitting the pool of values into the.textsegment at the end of the file.Convert jump tables (for the
tbhinstruction) to a form that works with the iOS assembler. The form commonly used in Linux generates a bad jump table under iOS—apparently the iOS assembler interprets the expressions differently.Convert “dot relative” expressions to a form that the iOS assembler correctly treats as assembly-time constants. This is a workaround for what looks very much like an iOS assembler bug that prevents incremental linking of the generated object files. (Or possibly it’s a bug in the iOS linker.) Details of the problem and the workaround are given in my blog post OCaml 4.00.0 on iOS: Progress Report. You can also see an example of this conversion below.
Remove uses of two pseudo-ops,
.typeand.size, when assembling for iOS. They aren’t supported by Apple’s assembler. This is done by defining null assembly macros for them.Define a macro
cbzwhen using ARM encodings for iOS. Thecbzinstruction is Thumb-only. The definition replaces it with a pair of ARM instructions.
You can download the script here:
The full text of the script is also included at the end of this post.
This is the fourth version of arm-as-to-ios, which seems to work for the OCaml 4.01.0 release as well as the 4.00.0 release that I wrote it for originally. But most likely it will change over time. As I make changes, I’ll keep the linked script up to date. If there are significant changes I’ll make another post about them.
If you want to try out arm-as-to-ios, copy and paste the lines from the end of this post into a file named arm-as-to-ios, or download it from the above link. Mark it as a script with chmod:
$ chmod +x arm-as-to-iosTo use the script, specify the name of an ARM assembly file. If no files are given, the script processes its standard input.
The following small example demonstrates the translations that arm-as-to-ios performs. Here is a small file of Linux ARM assembly code:
.syntax unified
.text
.align 2
.globl example
.type example, %function
example:
sub r10, r10, 8
cmp r10, r11
bcc 1f
bx lr
1:
ldr r7, =last_return_address
str lr, [r7]
bl .Lcall_gc
ldr lr, [r7]
b example
.Lcall_gc:
ldr r12, =bottom_of_stack
str sp, [r12]
bl garbage_collection
bx lr
/* Jump table fragment */
.Ljump:
tbh [pc, r4, lsl #1]
.short (.Ltest1-.)/2+0
.short (.Ltest2-.)/2+1
.short (.Ltest3-.)/2+2
.Ltest1:
ldr r4, [r4]
.Ltest2:
str r6, [sp, 8]
.Ltest3:
str r8, [r12]
/* Dot relative (frame table fragment) */
.word .L200000 - . + 0xfc000000
.long 0x1c9080
.thumb_func example
.word example
.short 8
.short 0
.L200000:
.asciz "example.ml"If you run arm-as-to-ios on this file, you get the following output that works for both Linux and iOS assemblers:
.syntax unified
/* Apple compatibility macros */
#if defined(SYS_macosx)
#define Glo(s) _##s
#define Loc(s) L##s
#if defined(MODEL_armv6)
.machine armv6
.macro .funtype
.endm
.macro cbz
cmp $0, #0
beq $1
.endm
#else
.machine armv7
.thumb
.macro .funtype
.thumb_func $0
.endm
#endif
.macro .type
.endm
.macro .size
.endm
#else
#define Glo(s) s
#define Loc(s) .L##s
.macro .funtype symbol
.type \symbol, %function
.endm
#endif
/* End Apple compatibility macros */
.text
.align 2
.globl Glo(example)
.funtype Glo(example)
Glo(example):
sub r10, r10, 8
cmp r10, r11
bcc 1f
bx lr
1:
ldr r7, Loc(Plast_return_address)
str lr, [r7]
bl Loc(call_gc)
ldr lr, [r7]
b Glo(example)
Loc(call_gc):
ldr r12, Loc(Pbottom_of_stack)
str sp, [r12]
bl Glo(garbage_collection)
bx lr
/* Jump table fragment */
Loc(jump):
tbh [pc, r4, lsl #1]
Loc(B27):
.short (Loc(test1)-Loc(B27))/2
.short (Loc(test2)-Loc(B27))/2
.short (Loc(test3)-Loc(B27))/2
Loc(test1):
ldr r4, [r4]
Loc(test2):
str r6, [sp, 8]
Loc(test3):
str r8, [r12]
/* Dot relative (frame table fragment) */
DR40 = Loc(200000) - . + 0xfc000000
.word DR40
.long 0x1c9080
.thumb_func Glo(example)
.word Glo(example)
.short 8
.short 0
Loc(200000):
.asciz "example.ml"
/* Pool of addresses loaded into registers */
.text
.align 2
Loc(Plast_return_address):
.long Glo(last_return_address)
Loc(Pbottom_of_stack):
.long Glo(bottom_of_stack)The output consists of a fixed prefix followed by the translation of the input file, followed by the pool of values to be loaded into registers.
The following shows a successful assembly for iOS of the arm.S file from OCaml 4.01.0, with the toolchain from Xcode 5.1.1 (OS X 10.9.2).
(Note: the arm.S from 4.01.0 requires a few changes that aren’t suited to arm-as-to-ios as a generally useful tool. To stay honest, I make the changes below using sed.)
$ HIDEOUT=/Applications/Xcode.app/Contents/Developer
$ TOOLCHAIN=$HIDEOUT/Toolchains/XcodeDefault.xctoolchain
$ CLANG=$TOOLCHAIN/usr/bin/clang
$ sed -i '' '/^#if defined(SYS_linux_eabihf)$/s/$/ || defined(SYS_macosx)/' arm.S
$ arm-as-to-ios arm.S > armcompat.S
$ $CLANG -no-integrated-as -arch armv7 -DSYS_macosx -c armcompat.S
$ file armcompat.o
armcompat.o: Mach-O object arm
$ otool -tv armcompat.o | head
armcompat.o:
(__TEXT,__text) section
_caml_call_gc:
00000000 f8dfc1e0 ldr.w r12, [pc, #0x1e0]
00000004 f8cce000 str.w lr, [r12]
00000008 f8dfc1dc ldr.w r12, [pc, #0x1dc]
0000000c f8ccd000 str.w sp, [r12]
00000010 ed2d0b10 vpush {d0, d1, d2, d3, d4, d5, d6, d7}
00000014 e92d50ff push.w {r0, r1, r2, r3, r4, r5, r6, r7, r12, lr}
00000018 f8dfc1d0 ldr.w r12, [pc, #0x1d0]The following shows the compatible file being generated and assembled under Debian ARMEL (ARM-based Linux system). Note that the generated file armcompat.S is identical to the above—the output of arm-as-to-ios is a single file that works in both environments.
$ sed -i '/^#if defined(SYS_linux_eabihf)$/s/$/ || defined(SYS_macosx)/' arm.S
$ ./arm-as-to-ios arm.S > armcompat.S
$ gcc -c -DSYS_linux_eabihf -c armcompat.S
$ file armcompat.o
armcompat.o: ELF 32-bit LSB relocatable, ARM, version 1 (SYSV), not stripped
$ objdump -d armcompat.o | grep -v '^$' | head
armcompat.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <caml_call_gc>:
0: f8df c1e0 ldr.w ip, [pc, #480] ; 1e4 <caml_system__code_end>
4: f8cc e000 str.w lr, [ip]
8: f8df c1dc ldr.w ip, [pc, #476] ; 1e8 <caml_system__code_end+0x4>
c: f8cc d000 str.w sp, [ip]
10: ed2d 0b10 vpush {d0-d7}
14: e92d 50ff stmdb sp!, {r0, r1, r2, r3, r4, r5, r6, r7, ip, lr}
18: f8df c1d0 ldr.w ip, [pc, #464] ; 1ec <caml_system__code_end+0x8>If you have any corrections, improvements, or encouragements, leave them below or email me at jeffsco@psellos.com. I’d be very pleased to hear if the script has been helpful to anyone.
Posted by: Jeffrey
Appendix
#!/usr/bin/env python
#
# arm-as-to-ios Modify ARM assembly code for the iOS assembler
#
# Copyright (c) 2012 Psellos http://psellos.com/
# Licensed under the MIT License:
# http://www.opensource.org/licenses/mit-license.php
#
# Resources for running OCaml on iOS: http://psellos.com/ocaml/
#
import sys
import re
VERSION = '1.4.0'
# Character classes for expression lexing.
#
g_ccid0 = '[$.A-Z_a-z\x80-\xff]' # Beginning of id
g_ccid = '[$.0-9A-Z_a-z\x80-\xff]' # Later in id
def ccc(cc): # Complement the class
if cc[1] == '^':
return cc[0] + cc[2:]
return cc[0] + '^' + cc[1:]
def ccce(cc): # Complement the class, include EOL
return '(?:' + ccc(cc) + '|$)'
# Prefixes for pooled symbol labels and jump table base labels. They're
# in the space of Linux assembler local symbols. Later rules will
# modify them to the Loc() form.
#
g_poolpfx = '.LP'
g_basepfx = '.LB'
def exists(p, l):
for l1 in l:
if p(l1):
return True
return False
def forall(p, l):
for l1 in l:
if not p(l1):
return False
return True
def add_prefix(instrs):
# Add compatibility macros for all systems, plus hardware
# definitions and compatibility macros for iOS.
#
# All systems:
#
# Glo() cpp macro for making global symbols (xxx vs _xxx)
# Loc() cpp macro for making local symbols (.Lxxx vs Lxxx)
# .funtype Expands to .thumb_func for iOS armv7 (null for armv6)
# Expands to .type %function for others
#
# iOS:
#
# .machine armv6/armv7
# .thumb (for armv7)
# cbz Expands to cmp/beq for armv6 (Thumb-only instr)
# .type Not supported by Apple assembler
# .size Not supported by Apple assembler
#
defre = '#[ \t]*if.*def.*SYS' # Add new defs near first existing ones
skipre = '$|\.syntax[ \t]' # Skip comment lines (and .syntax)
for i in range(len(instrs)):
if re.match(defre, instrs[i][1]):
break
else:
i = 0
for i in range(i, len(instrs)):
if not re.match(skipre, instrs[i][1]):
break
instrs[i:0] = [
('', '', '\n'),
('/* Apple compatibility macros */', '', '\n'),
('', '#if defined(SYS_macosx)', '\n'),
('', '#define Glo(s) _##s', '\n'),
('', '#define Loc(s) L##s', '\n'),
('', '#if defined(MODEL_armv6)', '\n'),
(' ', '.machine armv6', '\n'),
(' ', '.macro .funtype', '\n'),
(' ', '.endm', '\n'),
(' ', '.macro cbz', '\n'),
(' ', 'cmp $0, #0', '\n'),
(' ', 'beq $1', '\n'),
(' ', '.endm', '\n'),
('', '#else', '\n'),
(' ', '.machine armv7', '\n'),
(' ', '.thumb', '\n'),
(' ', '.macro .funtype', '\n'),
(' ', '.thumb_func $0', '\n'),
(' ', '.endm', '\n'),
('', '#endif', '\n'),
(' ', '.macro .type', '\n'),
(' ', '.endm', '\n'),
(' ', '.macro .size', '\n'),
(' ', '.endm', '\n'),
('', '#else', '\n'),
('', '#define Glo(s) s', '\n'),
('', '#define Loc(s) .L##s', '\n'),
(' ', '.macro .funtype symbol', '\n'),
(' ', '.type \\symbol, %function', '\n'),
(' ', '.endm', '\n'),
('', '#endif', '\n'),
('/* End Apple compatibility macros */', '', '\n'),
('', '', '\n')
]
return instrs
# Regular expression for modified ldr lines
#
g_ldre = '(ldr[ \t][^,]*,[ \t]*)=(([^ \t\n@,/]|/(?!\*))*)(.*)'
def explicit_address_loads(instrs):
# Linux assemblers allow the following:
#
# ldr rM, =symbol
#
# which loads rM with [mov] (immediately) if possible, or creates an
# entry in memory for the symbol value and loads it PC-relatively
# with [ldr].
#
# The Apple assembler doesn't seem to support this notation. If the
# value is a suitable constant, it emits a valid [mov]. Otherwise
# it seems to emit an invalid [ldr] that always generates an error.
# (At least I have not been able to make it work). So, change uses
# of =symbol to explicit PC-relative loads.
#
# This requires a pool containing the addresses to be loaded. For
# now, we just keep track of it ourselves and emit it into the text
# segment at the end of the file.
#
syms = {}
result = []
def repl1((syms, result), (a, b, c)):
global g_poolpfx
global g_ldre
(b1, b2, b3) = parse_iparts(b)
mo = re.match(g_ldre, b3, re.DOTALL)
if mo:
if mo.group(2) not in syms:
syms[mo.group(2)] = len(syms)
psym = mo.group(2)
if psym[0:2] == '.L':
psym = psym[2:]
newb3 = mo.group(1) + g_poolpfx + psym + mo.group(4)
result.append((a, b1 + b2 + newb3, c))
else:
result.append((a, b, c))
return (syms, result)
def pool1(result, s):
global g_poolpfx
psym = s
if psym[0:2] == '.L':
psym = psym[2:]
result.append(('', g_poolpfx + psym + ':', '\n'))
result.append((' ', '.long ' + s, '\n'))
return result
reduce(repl1, instrs, (syms, result))
if len(syms) > 0:
result.append(('', '', '\n'))
result.append(('/* Pool of addresses loaded into registers */',
'', '\n'))
result.append(('', '', '\n'))
result.append((' ', '.text', '\n'))
result.append((' ', '.align 2', '\n'))
reduce(pool1, sorted(syms, key=syms.get), result)
return result
def global_symbols(instrs):
# The form of a global symbol differs between Linux assemblers and
# the Apple assember:
#
# Linux: xxx
# Apple: _xxx
#
# Change occurrences of global symbols to use the Glo() cpp macro
# defined in our prefix.
#
# We consider a symbol to be global if:
#
# a. It appears in a .globl declaration; or
# b. It is referenced, has global form, and is not defined
#
glosyms = set()
refsyms = set()
defsyms = set()
result = []
def findglo1 (glosyms, (a, b, c)):
if re.match('#', b):
# Preprocessor line; nothing to do
return glosyms
(b1, b2, b3) = parse_iparts(b)
mo = re.match('(\.globl)' + ccce(g_ccid), b3)
if mo:
tokens = parse_expr(b3[len(mo.group(1)):])
if forall(lambda t: token_type(t) in ['space', 'id', ','], tokens):
for t in tokens:
if token_type(t) == 'id':
glosyms.add(t)
return glosyms
def findref1 ((refsyms, skipct), (a, b, c)):
def looksglobal(s):
if re.match('(r|a|v|p|c|cr|f|s|d|q|mvax|wcgr)[0-9]+$', s, re.I):
return False # numbered registers
if re.match('(wr|sb|sl|fp|ip|sp|lr|pc)$', s, re.I):
return False # named registers
if re.match('(fpsid|fpscr|fpexc|mvfr1|mvfr0)$', s, re.I):
return False # more named registers
if re.match('(mvf|mvd|mvfx|mvdx|dspsc)$', s, re.I):
return False # even more named registers
if re.match('(wcid|wcon|wcssf|wcasf|acc)$', s, re.I):
return False # even more named registers
if re.match('\.$|\.L|[0-9]|#', s):
return False # dot, local symbol, or number
if re.match('(asl|lsl|lsr|asr|ror|rrx)$', s, re.I):
return False # shift names
return True
if re.match('#', b):
# Preprocessor line; nothing to do
return (refsyms, skipct)
# Track nesting of .macro/.endm. For now, we don't look for
# global syms in macro defs. (Avoiding scoping probs etc.)
#
if skipct > 0 and re.match('\.(endm|endmacro)' + ccce(g_ccid), b):
return (refsyms, skipct - 1)
if re.match('\.macro' + ccce(g_ccid), b):
return (refsyms, skipct + 1)
if skipct > 0:
return (refsyms, skipct)
if re.match('\.(type|size|syntax|arch|fpu)' + ccce(g_ccid), b):
return (refsyms, skipct)
(b1, b2, b3) = parse_iparts(b)
rtokens = parse_rexpr(b3)
if len(rtokens) > 1 and rtokens[1] == '.req':
# .req has atypical syntax; no symbol refs there anyway
return (refsyms, skipct)
for t in rtokens[1:]:
if token_type(t) == 'id' and looksglobal(t):
refsyms.add(t)
return (refsyms, skipct)
def finddef1(defsyms, (a, b, c)):
if re.match('#', b):
# Preprocessor line
return defsyms
(b1, b2, b3) = parse_iparts(b)
rtokens = parse_rexpr(b3)
if b1 != '':
defsyms.add(b1)
if len(rtokens) > 1 and rtokens[1] == '.req':
defsyms.add(rtokens[0])
return defsyms
def repl1((glosyms, result), (a, b, c)):
if re.match('#', b):
# Preprocessor line
result.append((a, b, c))
return (glosyms, result)
toglo = lambda s: 'Glo(' + s + ')'
(b1, b2, b3) = parse_iparts(b)
tokens = parse_expr(b3)
if b1 in glosyms:
b1 = toglo(b1)
for i in range(len(tokens)):
if token_type(tokens[i]) == 'id' and tokens[i] in glosyms:
tokens[i] = toglo(tokens[i])
result.append((a, b1 + b2 + ''.join(tokens), c))
return (glosyms, result)
reduce(findglo1, instrs, glosyms)
reduce(findref1, instrs, (refsyms, 0))
reduce(finddef1, instrs, defsyms)
glosyms |= (refsyms - defsyms)
reduce(repl1, instrs, (glosyms, result))
return result
def local_symbols(instrs):
# The form of a local symbol differs between Linux assemblers and
# the Apple assember:
#
# Linux: .Lxxx
# Apple: Lxxx
#
# Change occurrences of local symbols to use the Loc() cpp macro
# defined in our prefix.
#
lsyms = set()
result = []
def find1 (lsyms, (a, b, c)):
mo = re.match('(\.L[^ \t:]*)[ \t]*:', b)
if mo:
lsyms.add(mo.group(1))
return lsyms
def repl1((lsyms, result), (a, b, c)):
matches = list(re.finditer('\.L[^ \t@:,+*/\-()]+', b))
if matches != []:
matches.reverse()
newb = b
for mo in matches:
if mo.group() in lsyms:
newb = newb[0:mo.start()] + \
'Loc(' + mo.group()[2:] + ')' + \
newb[mo.end():]
result.append((a, newb, c))
else:
result.append((a, b, c))
return (lsyms, result)
reduce(find1, instrs, lsyms)
reduce(repl1, instrs, (lsyms, result))
return result
def funtypes(instrs):
# Linux assemblers accept declarations like this:
#
# .type symbol, %function
#
# For Thumb functions, the Apple assembler wants to see:
#
# .thumb_func symbol
#
# Handle this by converting declarations to this:
#
# .funtype symbol
#
# Our prefix defines an appropriate .funtype macro for each
# environment.
#
result = []
def repl1(result, (a, b, c)):
mo = re.match('.type[ \t]+([^ \t,]*),[ \t]*%function', b)
if mo:
result.append((a, '.funtype ' + mo.group(1), c))
else:
result.append((a, b, c))
return result
reduce(repl1, instrs, result)
return result
def jump_tables(instrs):
# Jump tables for Linux assemblers often look like this:
#
# tbh [pc, rM, lsl #1]
# .short (.Labc-.)/2+0
# .short (.Ldef-.)/2+1
# .short (.Lghi-.)/2+2
#
# The Apple assembler disagrees about the meaning of this code,
# producing jump tables that don't work. Convert to the following:
#
# tbh [pc, rM, lsl #1]
# .LBxxx:
# .short (.Labc-.LBxxx)/2
# .short (.Ldef-.LBxxx)/2
# .short (.Lghi-.LBxxx)/2
#
# In fact we just convert sequences of .short pseudo-ops of the
# right form. There's no requirement that they follow a tbh
# instruction.
#
baselabs = []
result = []
def short_match(seq, op):
# Determine whether the op is a .short of the form that needs to
# be converted: .short (symbol-.)/2+k. If so, return a pair
# containing the symbol and the value of k. If not, return
# None. The short can only be converted if there were at least
# k other .shorts in sequence before the current one. A summary
# of the previous .shorts is in seq.
#
# (A real parser would do a better job, but this was quick to
# get working.)
#
sp = '([ \t]|/\*.*?\*/)*' # space
sp1 = '([ \t]|/\*.*?\*/)+' # at least 1 space
spe = '([ \t]|/\*.*?\*/|@[^\n]*)*$' # end-of-instr space
expr_re0 = (
'\.short' + sp + '\(' + sp + # .short (
'([^ \t+\-*/@()]+)' + sp + # symbol
'-' + sp + '\.' + sp + '\)' + sp + # -.)
'/' + sp + '2' + spe # /2 END
)
expr_re1 = (
'\.short' + sp + '\(' + sp + # .short (
'([^ \t+\-*/@()]+)' + sp + # symbol
'-' + sp + '\.' + sp + '\)' + sp + # -.)
'/' + sp + '2' + sp + # /2
'\+' + sp + # +
'((0[xX])?[0-9]+)' + spe # k END
)
expr_re2 = (
'\.short' + sp1 + # .short
'((0[xX])?[0-9]+)' + sp + # k
'\+' + sp + '\(' + sp + # +(
'([^ \t+\-*/@()]+)' + sp + # symbol
'-' + sp + '\.' + sp + '\)' + sp + # -.)
'/' + sp + '2' + spe # /2 END
)
mo = re.match(expr_re0, op)
if mo:
return(mo.group(3), 0)
mo = re.match(expr_re1, op)
if mo:
k = int(mo.group(11), 0)
if k > len(seq):
return None
return (mo.group(3), k)
mo = re.match(expr_re2, op)
if mo:
k = int(mo.group(2), 0)
if k > len(seq):
return None
return (mo.group(7), k)
return None
def conv1 ((baselabs, shortseq, label, result), (a, b, c)):
# Convert current instr (a,b,c) if it's a .short of the right
# form that spans a previous sequence of .shorts.
#
(b1, b2, b3) = parse_iparts(b)
if b3 == '':
# No operation: just note label if present.
result.append((a, b, c))
if re.match('\.L.', b1):
return (baselabs, shortseq, b1, result)
return (baselabs, shortseq, label, result)
if not re.match('.short[ \t]+[^ \t@]', b3):
# Not a .short: clear shortseq and label
result.append((a, b, c))
return (baselabs, [], '', result)
# We have a .short: figure out the label if any
if re.match('\.L', b1):
sl = b1
else:
sl = label
mpair = short_match(shortseq, b3)
if not mpair:
# A .short, but not of right form
shortseq.append((len(result), sl))
result.append((a, b, c))
return (baselabs, shortseq, '', result)
# OK, we have a .short to convert!
(sym, k) = mpair
shortseq.append((len(result), sl))
# Figure out base label (create one if necessary).
bx = len(shortseq) - 1 - k
bl = shortseq[bx][1]
if bl == '':
bl = g_basepfx + str(shortseq[bx][0])
shortseq[bx] = (shortseq[bx][0], bl)
baselabs.append(shortseq[bx])
op = '.short\t(' + sym + '-' + bl + ')/2'
result.append ((a, b1 + b2 + op, c))
return (baselabs, shortseq, '', result)
# Convert, accumulate result and new labels.
reduce(conv1, instrs, (baselabs, [], '', result))
# Add labels created here to the instruction stream.
baselabs.reverse()
for (ix, lab) in baselabs:
result[ix:0] = [('', lab + ':', '\n')]
# That does it
return result
def dot_relative(instrs):
# The Apple assembler (or possibly the linker) has trouble with code
# that looks like this:
#
# .word .Label - . + 0x80000000
# .word 0x1966
# .Label:
# .word 0x1967
#
# One way to describe the problem is that the assembler marks the
# first .word for relocation when in fact it's an assembly-time
# constant. Translate to the following form, which doesn't generate
# a relocation marking:
#
# DR0 = .Label - . + 0x80000000
# .word DR0
# .word 0x1966
# .Label:
# .word 0x1967
#
prefix = 'DR'
pseudos = '(\.byte|\.short|\.word|\.long|\.quad)'
result = []
def tok_ok(t):
return t in ['.', '+', '-', '(', ')'] or \
token_type(t) in ['space', 'locid', 'number']
def dotrel_match(expr):
# Determine whether the expression is one that needs to be
# translated.
tokens = parse_expr(expr)
return forall(tok_ok, tokens) and \
exists(lambda t: token_type(t) == 'locid', tokens) and \
exists(lambda t: token_type(t) == 'number', tokens) and \
exists(lambda t: t == '-', tokens) and \
exists(lambda t: t == '.', tokens)
def conv1(result, (a, b, c)):
if re.match('#', b):
# Preprocessor line
result.append((a, b, c))
else:
(b1, b2, b3) = parse_iparts(b)
mo = re.match(pseudos + ccce(g_ccid), b3)
if mo:
p = mo.group(1)
expr = b3[len(p):]
if dotrel_match(expr):
sym = prefix + str(len(result))
instr = sym + ' =' + expr
result.append(('', instr, '\n'))
result.append((a, b1 + b2 + p + ' ' + sym, c))
else:
result.append((a, b, c))
else:
result.append((a, b, c))
return result
reduce(conv1, instrs, result)
return result
def read_input():
# Concatenate all the input files into a string.
#
def fnl(s):
if s == '' or s[-1] == '\n':
return s
else:
return s + '\n'
if len(sys.argv) < 2:
return fnl(sys.stdin.read())
else:
input = ""
for f in sys.argv[1:]:
try:
fd = open(f)
input = input + fnl(fd.read())
fd.close()
except:
sys.stderr.write('arm-as-to-ios: cannot open ' + f + '\n')
return input
def parse_instrs(s):
# Parse the string into assembly instructions, also noting C
# preprocessor lines. Each instruction is represented as a triple:
# (space/comments, instruction, end). The end is either ';' or
# '\n'.
#
def goodmo(mo):
if mo == None:
# Should never happen
sys.stderr.write('arm-as-to-ios: internal parsing error\n')
sys.exit(1)
cpp_re = '([ \t]*)(#([^\n]*\\\\\n)*[^\n]*[^\\\\\n])\n'
comment_re = '[ \t]*#[^\n]*'
instr_re = (
'(([ \t]|/\*.*?\*/|@[^\n]*)*)' # Spaces & comments
'(([ \t]|/\*.*?\*/|[^;\n])*)' # "Instruction"
'([;\n])' # End
)
instrs = []
while s != '':
if re.match('[ \t]*#[ \t]*(if|ifdef|elif|else|endif|define)', s):
mo = re.match(cpp_re, s)
goodmo(mo)
instrs.append((mo.group(1), mo.group(2), '\n'))
elif re.match('[ \t]*#', s):
mo = re.match(comment_re, s)
goodmo(mo)
instrs.append((mo.group(0), '', '\n'))
else:
mo = re.match(instr_re, s, re.DOTALL)
goodmo(mo)
instrs.append((mo.group(1), mo.group(3), mo.group(5)))
s = s[len(mo.group(0)):]
return instrs
def parse_iparts(i):
# Parse an instruction into smaller parts, returning a triple of
# strings (label, colon, operation). The colon part also contains
# any surrounding spaces and comments (making the label and the
# operation cleaner to process).
#
# (Caller warrants that the given string doesn't start with space or
# a comment. This is true for strings returned by the instruction
# parser.)
#
lab_re = (
'([^ \t:/@]+)' # Label
'(([ \t]|/\*.*?\*/|@[^\n]*)*)' # Spaces & comments
':' # Colon
'(([ \t]|/\*.*?\*/|@[^\n]*)*)' # Spaces & comments
'([^\n]*)' # Operation
)
if len(i) > 0 and i[0] == '#':
# C preprocessor line; treat as operation.
return ('', '', i)
mo = re.match(lab_re, i)
if mo:
return (mo.group(1), mo.group(2) + ':' + mo.group(4), mo.group(6))
# No label, just an operation
return ('', '', i)
def parse_expr(s):
# Parse a string into a sequence of tokens. A segment of white
# space (including comments) is treated as a token, so that the
# tokens can be reassembled into the string again.
#
result = []
while s != '':
mo = re.match('([ \t]|/\*.*?\*/|@.*)+', s)
if not mo:
# Glo(...) and Loc(...) are single tokens
mo = re.match('(Glo|Loc)\([^()]*\)', s)
if not mo:
mo = re.match('"([^\\\\"]|\\\\.)*"', s)
if not mo:
mo = re.match(g_ccid0 + g_ccid + '*', s)
if not mo:
mo = re.match('[0-9]+[bf]', s)
if not mo:
mo = re.match('0[Xx][0-9a-fA-F]+|[0-9]+', s)
if not mo:
mo = re.match('.', s)
result.append(mo.group(0))
s = s[len(mo.group(0)):]
return result
def parse_rexpr(s):
# Like parse_expr(), but return only "real" tokens, not the
# intervening space.
#
return filter(lambda t: token_type(t) != 'space', parse_expr(s))
def token_type(t):
# Determine the type of a token. Caller warrants that it was
# returned by parse_expr() or parse_rexpr().
#
if re.match('[ \t]|/\*|@', t):
return 'space'
if re.match('Glo\(', t):
return 'gloid'
if re.match('Loc\(', t):
return 'locid'
if re.match('"', t):
return 'string'
if re.match(g_ccid0, t):
return 'id'
if re.match('[0-9]+[bf]', t):
return 'label'
if re.match('[0-9]', t):
return 'number'
return t # Sui generis
def debug_parse(a, b, c):
# Show results of instuction stream parse.
#
(b1, b2, b3) = parse_iparts(b)
newb = '{' + b1 + '}' + '{' + b2 + '}' + '{' + b3 + '}'
sys.stdout.write('{' + a + '}' + newb + c)
def main():
instrs = parse_instrs(read_input())
instrs = explicit_address_loads(instrs)
instrs = funtypes(instrs)
instrs = jump_tables(instrs)
instrs = global_symbols(instrs)
instrs = local_symbols(instrs)
instrs = dot_relative(instrs)
instrs = add_prefix(instrs)
for (a, b, c) in instrs:
sys.stdout.write(a + b + c)
main()