I've been working on an experimental port of jolt-burg. The main
difference is that my implementation language is Common Lisp and that my
compiler targets relocatable ELF object files.
Currently I have a compiler that can read sexp input, eg:
(define |main| (lambda ()
((call-c |dlsym| 0 "puts") "hello, dynamic world!")))
and then compile it down to a tree of blocks and instruction objects
(see instruction.lisp or Instruction.st)
BLOCK(--- NIL ---)
| | 0(--- VOID BLOCK --- 369
| | | | | 0(+++ REG CALLI4 ---
| | | | | | 0(+++ REG CNSTP4 --- reloc ---)
| | | | | | 0(+++ REG CNSTI4 --- 0)
| | | | | | 0(+++ REG CNSTP4 --- reloc ---))
| | | | | 0(+++ REG CNSTP4 --- reloc ---))
| | 0(--- VOID BLOCK --- 369
| | | | | 0(+++ REG CALLI4 EBX
| | | | | | 0(+++ REG CNSTP4 EBX reloc ---)
| | | | | | 0(+++ REG CNSTI4 EAX 0)
| | | | | | 0(+++ REG CNSTP4 ECX reloc ---))
| | | | | 0(+++ REG CNSTP4 EAX reloc ---))
This tree is processed by the burg compiler to emit x86 machine code.
(in the diagram we see registers being assigned to the tree nodes)
The last stage is when I collect the machine code generated by the burg
compiler and combine it with data and relocation entries to generate an
ELF object file.
I can then pass this to the unix linker (ld) to produce an executable.
ld --dynamic-linker=/lib/ld-linux.so.2 state/start.o state/hello.state.o
-ldl -lc -o myhello
Here you can see the disassembled elf object file with relocation
entries for the "dlsym" symbol and the "puts" and "hello world" strings.
objdump -d state/hello.state.o -r
Disassembly of section .text:
00000000 <main>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 53 push %ebx
4: 83 ec 14 sub $0x14,%esp
7: bb 00 00 00 00 mov $0x0,%ebx
8: R_386_32 dlsym
c: b8 00 00 00 00 mov $0x0,%eax
11: b9 00 00 00 00 mov $0x0,%ecx
12: R_386_32 _data_286
16: 89 4c 24 04 mov %ecx,0x4(%esp)
1a: 89 04 24 mov %eax,(%esp)
1d: ff d3 call *%ebx
1f: 89 c3 mov %eax,%ebx
21: b8 00 00 00 00 mov $0x0,%eax
22: R_386_32 _data_287
26: 89 04 24 mov %eax,(%esp)
29: ff d3 call *%ebx
2b: 89 c0 mov %eax,%eax
2d: 89 c0 mov %eax,%eax
2f: 83 c4 14 add $0x14,%esp
32: 5b pop %ebx
33: 5d pop %ebp
34: c3 ret
You can view the code at:
http://subvert-the-dominant-paradigm.net/repos/hgwebdir.cgi/bootstrap/
(click manifest to see the files, or run 'hg clone <url>' to get a local
copy)
John Leuner
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