Re: [9fans] Strings in acid, what am I missing?

[erik quanstrom <quanstro@quanstro.net>]

> *main:ca\s = *s<integer>*
> *(main:ca\s) = Hello
> *(main:cp\s) = $
>
> The first three values are expected, but when it gets to strings, I
> fail to understand what's happening.  What is the purpose of the
> parenthenses?  Why does 'cp' not give me the correct value and just
> gives me garbage instead?

part of the issue is, c does not have strings.  the other part is that
acid doesn't really understand c.  the reason that the () are required
is that * binds tighter than \s in acid.  one thing that's confusing about
acid is main:ca is an *address* of main:ca, not its value.  so *main:ca
is the pointer into the bss, and main:ca is the address of that pointer.

the reason cp gives you garbage is it's not initialized.  in fact when
i compile this for am64, you can see everthing quite clearly.  it is
optimized away!  (it's a good question why a char* is treated differently
than a char[].  perhaps there is some dark corner of the standard that
implies things.)

acid; asm(main)
main 0x00200028	SUBQ	$0x38,SP
main+0x4 0x0020002c	MOVL	$0xa,x+0x34(SP)		// x = 10
main+0xc 0x00200034	LEAQ	x+0x34(SP),AX		// ip = &x
main+0x11 0x00200039	MOVL	$0x1,ia+0x1c(SP)		// ia[0] = 1
main+0x19 0x00200041	MOVL	$0x2,0x20(SP)		// ia[1] = 2
main+0x21 0x00200049	MOVL	$0x3,0x24(SP)		// ia[2] = 3
main+0x29 0x00200051	MOVB	$0x48,ca+0x16(SP)	// ca[0] = 'H'
main+0x2e 0x00200056	MOVB	$0x65,0x17(SP)		// ca[1] = 'e'
main+0x33 0x0020005b	MOVB	$0x6c,0x18(SP)		// ca[1] = 'l'
main+0x38 0x00200060	MOVB	$0x6c,0x19(SP)		// ca[1] = 'l'
main+0x3d 0x00200065	MOVB	$0x6f,0x1a(SP)		// ca[1] = 'o'
main+0x42 0x0020006a	MOVB	$0x0,0x1b(SP)		// ca[1] = '\0'
main+0x47 0x0020006f	MOVL	$.string(SB),AX
main+0x4c 0x00200074	XORQ	BP,BP			// 1st argument to exits -> 0
main+0x4f 0x00200077	CALL	exits(SB)
main+0x54 0x0020007c	ADDQ	$0x38,SP
main+0x58 0x00200080	RET
_main 0x00200081	SUBQ	$0x90,SP

you can also see this in the compile output:

; tmk q.c
6c -FVTw q.c
warning: q.c:11 auto declared and not used: cp
warning: q.c:10 auto declared and not used: ca
warning: q.c:9 auto declared and not used: ia
warning: q.c:8 auto declared and not used: ip
warning: q.c:8 set and not used: ip
warning: q.c:11 set and not used: cp
6l -o 6.q q.6

- erik