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Added some notes about how the JIT works

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David Anderson 2004-09-16 20:31:38 +00:00
parent 2f1de39dd3
commit c90d922443
1 changed files with 22 additions and 1 deletions
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23
amxmodx/JIT/jits.asm
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@ -153,6 +153,7 @@ _dbgcode: resd 1
_dbgaddr: resd 1
_dbgparam: resd 1
_dbgname: resd 1
;usertags and userdata are 16 bytes on AMX Mod X
_usertags1: resd 1 ; 4 = AMX_USERNUM (#define'd in amx.h)
_usertags2: resd 1 ; 4 = AMX_USERNUM (#define'd in amx.h)
_usertags3: resd 1 ; 4 = AMX_USERNUM (#define'd in amx.h)
@ -277,6 +278,14 @@ AMX_FLAG_RELOC equ 8000h ; jump/call addresses relocated
;
; This is the work horse of the whole JIT: It actually copies the code.
; Notes from ~dvander (with help of dJeyL)
; This takes a source and ending address pointer in the assembled JIT code.
; Then it subtracts them and copies the code in between.
; The last parameter is the number of bytes the opcode is so it can jump
; to the next one.
; Also note that the "in between" code is NEVER executed during the compile
; phase of the JIT. It's only assembled in memory, and copied into the
; final output bytecode by this function.
%macro GO_ON 2-3 4
mov esi, %1 ;get source address of JIT code
mov ecx,%2-%1 ;get number of bytes to copy
@ -292,6 +301,8 @@ AMX_FLAG_RELOC equ 8000h ; jump/call addresses relocated
; Nasm can't handle the determination of the maximum code size as was done
; in the Masm implementation, since it only does two passes. This macro is
; called *after* the code for each Small instruction.
; Notes by ~dvander: This just substracts a label's ip from the current ip.
; Therefore you get an instant size check - see RELOC
%macro CHECKCODESIZE 1
%if MAXCODESIZE < $-%1
%assign MAXCODESIZE $-%1
@ -302,6 +313,11 @@ AMX_FLAG_RELOC equ 8000h ; jump/call addresses relocated
; Modify the argument of an x86 instruction with the Small opcode's parameter
; before copying the code.
;
; Notes by ~dvander (thanks to dJeyL) - this will take an address and modify
; the dword at it. Since the JIT copies already assembled code, you see
; things like "call 12345678h". This is an arbitrary value as putval
; will modify it in memory and then GO_ON will add it to the program.
; It is important to get the putval address right - it's in bytes.
%macro putval 1
mov eax,[ebx+4]
mov dword [%1],eax
@ -310,7 +326,12 @@ AMX_FLAG_RELOC equ 8000h ; jump/call addresses relocated
;
; Add an entry to the table of addresses which have to be relocated after the
; code compilation is done.
;
; Notes by ~dvander: This is sort of what amx_BrowseRelocate() does, although
; relocation is actually done after code generation (this just adds to a
; table). Like putval, this takes in an address and marks it to be
; rewritten. It is a good idea to just use labels to find relocation
; offsets (see OP_CALL and OP_RETN). After code generation, this table
; is browsed and the correct threaded jumps are placed.
%macro RELOC 1-2 ; adr, dest
mov ebp,[reloc_num]
%if %0 < 2