Machine code: Difference between revisions

=={{header|Smalltalk}}==

I agree that this is more harmful than useful. The only target audience are compiler writers and Smalltalk-core developers (of which I guess are not too many around).

Also, this is highly cpu specific, the task is for an x86 and also assuming a particular calling convention; both is probably (definitely) not the case (most, incl. myself are on 64bit machines these days).

Anyway, as a sketch, here is how to do it (I won't waste time in making an x86_64 version for the particular calling convention used on my machine; and yes: it is even different between Unix and Windows systems!):

First we need a way to allocate executable memory (btw. we should probably also care to flush any instruction caches, which I won't go into here);

This is very Smalltalk dialect specific, and probably not supported on other Smalltalks; in ST/X, we can define it as:

{{works with|Smalltalk/X}}

<lang smalltalk>!ExternalBytes class methods!

mapExecutableBytes:size

%{

# include <sys/mman.h>

void *mem;

OBJ retVal;

int nBytes = __intVal(size);

mem = mmap(nil, nBytes, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0);

if (mem != MAP_FAILED) {

RETURN( __MKEXTERNALBYTES_N(mem, nBytes));

}

%}.

self primitiveFailed

! !</lang>

next, we need the correct code; the following presents the x86 version (but do not expect this code to NOT crash the Smalltalk VM, as the calling convention is certainly wrong..)

<lang smalltalk>OperatingSystem getCPUType = #'x86' ifTrue:[

code := #[0x8B 0x44 0x24 0x04 0x03 0x44 0x24 0x08 0xC3].

] ifFalse:[

self error:'unsupported cpu'

].

handle := ExternalBytes mapExecutableBytes:100.

handle replaceFrom:1 with:code.

" dump it (debugging only)... "

e'code at {handle address hexPrintString} is:' printCR.

(handle copyFrom:1 to:50) asByteArray hexPrintString printCR.

" create an ExternalFunction for it "

func := ExternalLibraryFunction new code:handle address.

func name:'unnamed' module:nil returnType:#int argumentTypes:#(int int).

func beCallTypeC.

func printCR.

" now call it "

result := func invokeWithArguments:{10 . 20}

</lang>

With a few more tricks, it is even possible to install that function as a method in a class; but additional code needs to be generated, to assert that the passed data is correctly boxed/unboxed.