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6c: extern register fix (import from patch/6c-extreg)

to make it easy to use normal libraries (such as libdraw, libsec, and libmp)
with the kernel, which uses extern register, don't stray into the external
register set when allocating values to registers.

--- a/amd64/include/u.h

+++ b/amd64/include/u.h

@@ -10,7 +10,7 @@

 typedef unsigned long	usize;

 typedef	ushort		Rune;

 typedef union FPdbleword FPdbleword;

-typedef uvlong		jmp_buf[2];

+typedef uintptr		jmp_buf[2];

 #define	JMPBUFSP	0

 #define	JMPBUFPC	1

 #define	JMPBUFDPC	0

--- a/sys/src/cmd/6c/reg.c

+++ b/sys/src/cmd/6c/reg.c

@@ -50,6 +50,8 @@

 	lastr = R;

 	nvar = 0;

 	regbits = RtoB(D_SP) | RtoB(D_AX) | RtoB(D_X0);

+	if(REGEXT)

+		regbits |= RtoB(REGEXT) | RtoB(REGEXT-1);

 	for(z=0; z<BITS; z++) {

 		externs.b[z] = 0;

 		params.b[z] = 0;

--- a/sys/src/cmd/6c/txt.c

+++ b/sys/src/cmd/6c/txt.c

@@ -1,5 +1,7 @@

 #include "gc.h"

+static	int	resvreg[nelem(reg)];

+

 void

 ginit(void)

 {

@@ -94,6 +96,7 @@

 	if(0)

 		com64init();

+	memset(reg, 0, sizeof(reg));

 	for(i=0; i<nelem(reg); i++) {

 		reg[i] = 1;

 		if(i >= D_AX && i <= D_R15 && i != D_SP)

@@ -101,6 +104,10 @@

 		if(i >= D_X0 && i <= D_X7)

 			reg[i] = 0;

 	}

+	/* keep two external registers */

+	reg[REGEXT] = 1;

+	reg[REGEXT-1] = 1;

+	memmove(resvreg, reg, sizeof(resvreg));

 }

 void

@@ -111,10 +118,10 @@

 	reg[D_SP]--;

 	for(i=D_AX; i<=D_R15; i++)

-		if(reg[i])

+		if(reg[i] && !resvreg[i])

 			diag(Z, "reg %R left allocated", i);

 	for(i=D_X0; i<=D_X7; i++)

-		if(reg[i])

+		if(reg[i] && !resvreg[i])

 			diag(Z, "reg %R left allocated", i);

 	while(mnstring)

 		outstring("", 1L);

@@ -179,7 +186,7 @@

 	n = 0;

 	for(i=D_AX; i<=D_R15; i++)

-		if(reg[i] == 0)

+		if(reg[i] == 0 && !resvreg[i])

 			n++;

 	return n;

 }

@@ -337,7 +344,7 @@

 				goto out;

 		}

 		for(i=D_AX; i<=D_R15; i++)

-			if(reg[i] == 0)

+			if(reg[i] == 0 && !resvreg[i])

 				goto out;

 		diag(tn, "out of fixed registers");

 		goto err;

@@ -350,7 +357,7 @@

 				goto out;

 		}

 		for(i=D_X0; i<=D_X7; i++)

-			if(reg[i] == 0)

+			if(reg[i] == 0 && !resvreg[i])

 				goto out;

 		diag(tn, "out of float registers");

 		goto out;

--- a/sys/src/cmd/6l/span.c

+++ b/sys/src/cmd/6l/span.c

@@ -668,6 +668,9 @@

 	rex &= (0x40 | Rxr);

 	v = a->offset;

+	if ((vlong)v != a->offset) 

+		print("asmandsz: Trying to emit %#ullx and 32 bits is not sufficient\n",

+			a->offset);

 	t = a->type;

 	if(a->index != D_NONE) {

 		if(t >= D_INDIR) {

-- 

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