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Rev	Author	Line No.	Line
2	-	1	`/*`
		2	`* Far call, absolute indirect.`
		3	`* The argument is the offset.`
		4	`* We use a global structure for the jump params,`
		5	`* so this is not reentrant or thread safe.`
		6	`*/`
		7
		8	`#include "mem.h"`
		9
		10	`#define SSOVERRIDE BYTE $0x36`
		11	`#define CSOVERRIDE BYTE $0x2E`
		12	`#define RETF BYTE $0xCB`
		13
		14	`GLOBL apmjumpstruct+0(SB), $8`
		15
		16	`TEXT fortytwo(SB), $0`
		17	`MOVL $42, AX`
		18	`RETF`
		19
		20	`TEXT getcs(SB), $0`
		21	`PUSHL CS`
		22	`POPL AX`
		23	`RET`
		24
		25	`TEXT apmfarcall(SB), $0`
		26	`/*`
		27	`* We call push and pop ourselves.`
		28	`* As soon as we do the first push or pop,`
		29	`* we can't use FP anymore.`
		30	`*/`
		31	`MOVL off+4(FP), BX`
		32	`MOVL seg+0(FP), CX`
		33	`MOVL BX, apmjumpstruct+0(SB)`
		34	`MOVL CX, apmjumpstruct+4(SB)`
		35
		36	`/* load necessary registers from Ureg */`
		37	`MOVL ureg+8(FP), DI`
		38	`MOVL 28(DI), AX`
		39	`MOVL 16(DI), BX`
		40	`MOVL 24(DI), CX`
		41	`MOVL 20(DI), DX`
		42
		43	`/* save registers, segments */`
		44	`PUSHL DS`
		45	`PUSHL ES`
		46	`PUSHL FS`
		47	`PUSHL GS`
		48	`PUSHL BP`
		49	`PUSHL DI`
		50
		51	`/*`
		52	`* paranoia: zero the segments, since it's the`
		53	`* BIOS's responsibility to initialize them.`
		54	`* (trick picked up from Linux driver).`
		55	`PUSHL DX`
		56	`XORL DX, DX`
		57	`PUSHL DX`
		58	`POPL DS`
		59	`PUSHL DX`
		60	`POPL ES`
		61	`PUSHL DX`
		62	`POPL FS`
		63	`PUSHL DX`
		64	`POPL GS`
		65	`POPL DX`
		66	`*/`
		67
		68	`PUSHL $APMDSEG`
		69	`POPL DS`
		70
		71	`/*`
		72	`* The actual call.`
		73	`*/`
		74	`CSOVERRIDE; BYTE $0xFF; BYTE $0x1D`
		75	`LONG $apmjumpstruct+0(SB)`
		76
		77	`/* restore segments, registers */`
		78	`POPL DI`
		79	`POPL BP`
		80	`POPL GS`
		81	`POPL FS`
		82	`POPL ES`
		83	`POPL DS`
		84
		85	`PUSHFL`
		86	`POPL 64(DI)`
		87
		88	`/* store interesting registers back in Ureg */`
		89	`MOVL AX, 28(DI)`
		90	`MOVL BX, 16(DI)`
		91	`MOVL CX, 24(DI)`
		92	`MOVL DX, 20(DI)`
		93	`MOVL SI, 4(DI)`
		94
		95	`PUSHFL`
		96	`POPL AX`
		97	`ANDL $1, AX /* carry flag */`
		98	`RET`

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(root)/os/branches/feature_unix/sys/src/9/pc/apmjump.s – Rev 2