Reworked VC4 relocations and some of the instruction encoding to be actually correct. Now generating what could be real code!

--HG--
branch : dtrg-videocore

mach/vc4/as/mach5.c

@@ -7,6 +7,11 @@
 
 #define maskx(v, x) (v & ((1<<(x))-1))
 
+static void toobig(void)
+{
+	serror("offset too big to encode into instruction");
+}
+
 /* Assemble an ALU instruction where rb is a register. */
 
 void alu_instr_reg(quad op, int cc, int rd, int ra, int rb)
@@ -90,6 +95,7 @@ void misc_instr_lit(quad op, int cc, int rd, int ra, quad value)
 
 void branch_instr(int bl, int cc, struct expr_t* expr)
 {
+	quad pc = DOTVAL;
 	quad type = expr->typ & S_TYP;
 
 	/* Sanity checking. */
@@ -114,7 +120,7 @@ void branch_instr(int bl, int cc, struct expr_t* expr)
 			/* The VC4 branch instructions express distance in 2-byte
 			 * words. */
 
-			int d = (expr->val - DOTVAL) / 2;
+			int d = (expr->val - pc) / 2;
 
         	/* We now know the worst case for the instruction layout. At
         	 * this point we can emit the instructions, which may shrink
@@ -126,7 +132,7 @@ void branch_instr(int bl, int cc, struct expr_t* expr)
         	     * close enough to the program counter, we can use a short-
         	     * form instruction. */
 
-        	    if ((d >= -128) && (d < 127))
+        	    if (fitx(d, 7))
         	    {
 					emit2(B16(00011000,00000000) | (cc<<7) | (d&0x7f));
 					break;
@@ -140,15 +146,25 @@ void branch_instr(int bl, int cc, struct expr_t* expr)
 
 			if (bl)
 			{
-				quad v = d & 0x07ffffff;
+				quad v, hiv, lov;
-				quad hiv = v >> 23;
+
-				quad lov = v & 0x007fffff;
+				if (!fitx(d, 27))
+					toobig();
+
+				v = maskx(d, 27);
+				hiv = v >> 23;
+				lov = v & 0x007fffff;
 				emit2(B16(10010000,10000000) | (lov>>16) | (hiv<<8));
 				emit2(B16(00000000,00000000) | (lov&0xffff));
 			}
 			else
 			{
-				quad v = d & 0x007fffff;
+				quad v;
+
+				if (!fitx(d, 23))
+					toobig();
+
+				v = maskx(d, 23);
 				emit2(B16(10010000,00000000) | (cc<<8) | (v>>16));
 				emit2(B16(00000000,00000000) | (v&0xffff));
 			}
@@ -334,6 +350,8 @@ void mem_postincr_instr(quad opcode, int cc, int rd, int rs)
 
 void mem_address_instr(quad opcode, int rd, struct expr_t* expr)
 {
+	static const char sizes[] = {4, 2, 1, 2};
+	int size = sizes[opcode];
 	quad type = expr->typ & S_TYP;
 
 	/* Sanity checking. */
@@ -354,10 +372,7 @@ void mem_address_instr(quad opcode, int rd, struct expr_t* expr)
 		case 1:
 		case 2:
 		{
-			/* The VC4 branch instructions express distance in 2-byte
+			int d = expr->val - DOTVAL;
-			 * words. */
-
-			int d = (expr->val - DOTVAL) / 2;
 
         	/* We now know the worst case for the instruction layout. At
         	 * this point we can emit the instructions, which may shrink
@@ -365,25 +380,31 @@ void mem_address_instr(quad opcode, int rd, struct expr_t* expr)
 
 			if (type == DOTTYP)
 			{
+				int scaledd = d/size;
+
         	    /* This is a reference to an address within this section. If
         	     * it's close enough to the program counter, we can use a
         	     * shorter instruction. */
 
-				if (fitx(d, 16))
+				if (fitx(scaledd, 16))
 				{
                     emit2(B16(10101010,00000000) | (opcode<<5) | (rd<<0));
-                    emit2(d);
+                    emit2(scaledd);
                     return;
                 }
 			}
 
 			/* Otherwise we need the full 48 bits. */
 
-            if (!fitx(d, 27))
-                serror("offset too big to encode into instruction");
-
 			newrelo(expr->typ, RELOVC4|RELPC);
 
+			/* VC4 relocations store the PC-relative delta into the
+			 * destination section in the instruction data. The linker will
+			 * massage this, and scale it appropriately. */
+
+            if (!fitx(d, 27))
+				toobig();
+
             emit2(B16(11100111,00000000) | (opcode<<5) | (rd<<0));
             emit4((31<<27) | maskx(d, 27));
 			break;
@@ -493,8 +514,19 @@ void lea_stack_instr(int rd, long va, int rs)
 
 void lea_address_instr(int rd, struct expr_t* expr)
 {
-	newrelo(expr->typ, RELOVC4);
+	quad pc = DOTVAL;
+	quad type = expr->typ & S_TYP;
+
+	if (type == S_ABS)
+		serror("can't use absolute addresses here");
+
+	newrelo(expr->typ, RELOVC4|RELPC);
+
+	/* VC4 relocations store the PC-relative delta into the
+	 * destination section in the instruction data. The linker will
+	 * massage this, and scale it appropriately. */
+
 	emit2(B16(11100101,00000000) | (rd<<0));
-	emit4(expr->val);
+	emit4(expr->val - pc);
 }
 

mach/vc4/libem/dummy.s

@@ -7,3 +7,8 @@
  */
 
 #include "videocore.h"
+
+.define	__dummy
+.sect .data
+__dummy:
+

plat/rpi/boot.s

@@ -16,6 +16,10 @@
 .sect .text
 
 begtext:
+	lea r15, begtext
+	st sp, .returnsp
+	st lr, .returnlr
+
 #if 0
 	! Wipe the bss. (I'm a little suprised that __m_a_i_n doesn't do this.)
 	
@@ -33,6 +37,12 @@ begtext:
 #endif
 	b __m_a_i_n
 
+.define __exit
+__exit:
+	ld sp, .returnsp
+	ld lr, .returnlr
+	b lr
+
 ! Define symbols at the beginning of our various segments, so that we can find
 ! them. (Except .text, which has already been done.)
 
@@ -47,3 +57,9 @@ begtext:
 .comm .trppc, 4
 .comm .ignmask, 4
 .comm _errno, 4
+
+! We store the stack pointer and return address on entry so that we can
+! cleanly exit.
+
+.comm .returnsp, 4
+.comm .returnlr, 4

util/led/relocate.c

@@ -8,6 +8,7 @@ static char rcsid[] = "$Id$";
 
 #include <stdlib.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <assert.h>
 #include "out.h"
 #include "const.h"
@@ -44,6 +45,65 @@ static long read4(char* addr, int type)
 		return ((long)word1 << (2 * WIDTH)) + word0;
 }
 
+/* VideoCore 4 fixups are complex as we need to patch the instruction in
+ * one of several different ways (depending on what the instruction is).
+ */
+
+static long get_vc4_valu(char* addr)
+{
+	uint16_t opcode = read2(addr, 0);
+
+	if ((opcode & 0xff00) == 0xe700)
+	{
+		/* ld<w> rd, $+o:  [1110 0111 ww 0 d:5] [11111 o:27]
+		 * st<w> rd, $+o:  [1110 0111 ww 1 d:5] [11111 o:27]
+		 */
+
+		int32_t value = read4(addr+2, 0);
+		value &= 0x07ffffff;
+		value = value<<5>>5;
+		return value;
+	}
+
+	if ((opcode & 0xf080) == 0x9000)
+	{
+		/* b<cc> $+o*2:  [1001 cccc 0ooo oooo] [oooo oooo oooo oooo]
+		 * Yes, big-endian (the first 16 bits is the MSB).
+		 */
+
+		uint32_t value = read4(addr, RELWR);
+		value &= 0x007fffff;
+		value = value<<9>>9;
+		value *= 2;
+		return value;
+	}
+
+	if ((opcode & 0xf080) == 0x9080)
+	{
+		/* bl $+o*2:  [1001 oooo 1ooo oooo] [oooo oooo oooo oooo]
+		 * Yes, big-endian (the first 16 bits is the MSB).
+		 * (Note that o is split.)
+		 */
+
+		int32_t value = read4(addr, RELWR);
+		int32_t lov = value & 0x007fffff;
+		int32_t hiv = value & 0x0f000000;
+		value = lov | (hiv>>1);
+		value = value<<5>>5;
+		value *= 2;
+		return value;
+	}
+
+	if ((opcode & 0xffe0) == 0xe500)
+	{
+        /* lea: [1110 0101 000 d:5] [o:32] */
+
+        return read4(addr+2, 0);
+    }
+
+	assert(0 && "unrecognised VC4 instruction");
+}
+
 /*
  * The bits in type indicate how many bytes the value occupies and what
  * significance should be attributed to each byte.
@@ -65,21 +125,7 @@ getvalu(addr, type)
 	case RELOH2:
 		return read2(addr, type) << 16;
 	case RELOVC4:
-	{
+		return get_vc4_valu(addr);
-		long i = read4(addr, type);
-		if (i & 0x00800000)
-		{
-            /* Branch instruction. */
-            return (i<<9)>>9;
-		}
-		else
-		{
-			/* Branch-link instruction. */
-			long hi = (i<<4)>>28;
-			long lo = (i & 0x007fffff);
-			return lo | (hi<<23);
-		}
-	}
 	default:
 		fatal("bad relocation size");
 	}
@@ -123,6 +169,60 @@ static void write4(long valu, char* addr, int type)
 	}
 }
 
+/* VideoCore 4 fixups are complex as we need to patch the instruction in
+ * one of several different ways (depending on what the instruction is).
+ */
+
+static void put_vc4_valu(char* addr, long value)
+{
+	uint16_t opcode = read2(addr, 0);
+
+	if ((opcode & 0xff00) == 0xe700)
+	{
+		/* ld<w> rd, o, (pc):  [1110 0111 ww 0 d:5] [11111 o:27]
+		 * st<w> rd, o, (pc):  [1110 0111 ww 1 d:5] [11111 o:27]
+		 */
+
+		uint32_t v = read4(addr+2, 0);
+		v &= 0xf8000000;
+		v |= value & 0x07ffffff;
+		write4(v, addr+2, 0);
+	}
+	else if ((opcode & 0xf080) == 0x9000)
+	{
+		/* b<cc> dest:  [1001 cccc 0ooo oooo] [oooo oooo oooo oooo]
+		 * Yes, big-endian (the first 16 bits is the MSB).
+		 */
+
+		uint32_t v = read4(addr, RELWR);
+		v &= 0xff800000;
+		v |= (value/2) & 0x007fffff;
+		write4(v, addr, RELWR);
+	}
+	else if ((opcode & 0xf080) == 0x9080)
+	{
+		/* bl dest:  [1001 oooo 1ooo oooo] [oooo oooo oooo oooo]
+		 * Yes, big-endian (the first 16 bits is the MSB).
+		 * (Note that o is split.)
+		 */
+
+		uint32_t v = read4(addr, RELWR);
+		uint32_t lovalue = (value/2) & 0x007fffff;
+		uint32_t hivalue = (value/2) & 0x07800000;
+		v &= 0xf0800000;
+		v |= lovalue | (hivalue<<1);
+		write4(v, addr, RELWR);
+	}
+	else if ((opcode & 0xffe0) == 0xe500)
+	{
+        /* lea: [1110 0101 000 d:5] [o:32] */
+
+		write4(value, addr+2, 0);
+    }
+    else
+		assert(0 && "unrecognised VC4 instruction");
+}
+
 /*
  * The bits in type indicate how many bytes the value occupies and what
  * significance should be attributed to each byte.
@@ -156,27 +256,8 @@ putvalu(valu, addr, type)
 		write2(valu>>16, addr, type);
 		break;
 	case RELOVC4:
-	{
+		put_vc4_valu(addr, valu);
-		long i = read4(addr, type);
-		if (i & 0x00800000)
-		{
-			/* Branch instruction. */
-			unsigned v = (valu/2) & 0x007fffff;
-			i &= ~0x007fffff;
-			i |= v;
-		}
-		else
-		{
-			/* Branch-link instruction. */
-	        unsigned v = (valu/2) & 0x07ffffff;
-	        unsigned hiv = v >> 23;
-	        unsigned lov = v & 0x007fffff;
-			i &= ~0x0f7fffff;
-			i |= (lov>>16) | (hiv<<24);
-		}
-		write4(i, addr, type);
 		break;
-	}
 	default:
 		fatal("bad relocation size");
 	}