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5e: enable VFP emulation by default, doubles only need to be 4 byte aligned

this adds -F flag to 5e (same as 5l) to disable VFP emulation
and makes VFP emulation the default.

--- a/sys/man/1/5e

+++ b/sys/man/1/5e

@@ -4,7 +4,7 @@

 .SH SYNOPSIS

 .B 5e

 [

-.B -npb

+.B -npbF

 ]

 .I text

 [

@@ -92,6 +92,9 @@

 instead of

 .I sysfatal.

 See below.

+.TP

+.B -F

+Disable emulation of VFP floating point instructions.

 .SH SOURCE

 .B /sys/src/cmd/5e

 .SH SEE ALSO

@@ -108,13 +111,6 @@

 notes.

 Obscure opcodes, in particular uncommon operations on R15, are not implemented.

-Careless use of the

-.B LDREX

-and

-.B STREX

-instructions can lead to deadlock, while the

-.I ARM Architecture Reference Manual

-indicates a real processor will exhibit undefined behavior in these cases.

 Accesses spanning segment boundaries will be treated as page faults.

 Many syscalls such as

--- a/sys/src/cmd/5e/5e.c

+++ b/sys/src/cmd/5e/5e.c

@@ -4,6 +4,7 @@

 #include "dat.h"

 #include "fns.h"

+int vfp = 1;

 int nflag, pflag, bflag;

 Ref nproc;

@@ -49,7 +50,7 @@

 static void

 usage(void)

 {

-	fprint(2, "usage: 5e [-npbf] text [...]\n");

+	fprint(2, "usage: 5e [-npbF] text [...]\n");

 	exits(nil);

 }

@@ -105,6 +106,7 @@

 	case 'p': pflag++; break;

 	case 'b': bflag++; break;

 	case 'f': vfp = 1; break;

+	case 'F': vfp = 0; break;

 	default: usage();

 	} ARGEND;

 	if(argc < 1)

--- a/sys/src/cmd/5e/vfp.c

+++ b/sys/src/cmd/5e/vfp.c

@@ -55,7 +55,7 @@

 	sz = instr & (1<<8);

 	if((instr & (1<<23)) == 0)

 		off = -off;

-	ea = vaddr(evenaddr(P->R[n] + off, sz ? 7 : 3), 8, &seg);

+	ea = vaddr(evenaddr(P->R[n] + off, 3), sz ? 8 : 4, &seg);

 	switch((instr>>20)&0x3){

 	case 0:

 		if(sz)