[riscv] Allow apply_relocs() to use non-inline relocation records

The address of the compressed relocation records is currently
calculated implicitly relative to the program counter.  This requires
the relocation records to be copied as part of relocation to a new
physical address, so that they can be reapplied (if needed) after
copying iPXE to the new physical address.

Since the relocation destination will never overlap the original iPXE
image, and since the relocation records will not be needed further
after completing relocation, we can avoid the need to copy the records
by passing in a pointer to the relocation records present in the
original iPXE image.

Pass the compressed relocation record address as an explicit parameter
to apply_relocs(), rather than being implicit in the program counter.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/riscv/prefix/libprefix.S

@@ -227,7 +227,9 @@ print_hex_value_alt:
  * records are overlaid with .bss).  It does not require a valid stack
  * pointer.
  *
- * Parameters: none (address is implicit in the program counter)
+ * Parameters: none
+ *
+ *   a0 - Relocation records
  *
  * Returns: none
  *
@@ -241,27 +243,26 @@ print_hex_value_alt:
 apply_relocs:
 	/* Register usage:
 	 *
-	 * a0 - relocation addend
+	 * a0 - current relocation record pointer
 	 * a1 - current relocation target address
-	 * a2 - current relocation record pointer
+	 * a2 - relocation addend
 	 * a3 - current relocation record value
 	 * a4 - number of bits remaining in current relocation record
 	 */
 	la	a1, _prefix
-	la	a2, _edata
 
 	/* Calculate relocation addend */
-	LOADN	a0, prefix_virt
-	sub	a0, a1, a0
+	LOADN	a2, prefix_virt
+	sub	a2, a1, a2
 
 	/* Skip applying relocations if addend is zero */
-	beqz	a0, apply_relocs_done
+	beqz	a2, apply_relocs_done
 	progress " reloc"
 
 apply_relocs_loop:
 	/* Read new relocation record */
-	LOADN	a3, (a2)
-	addi	a2, a2, ( __riscv_xlen / 8 )
+	LOADN	a3, (a0)
+	addi	a0, a0, ( __riscv_xlen / 8 )
 	li	a4, ( __riscv_xlen - 1 )
 
 	/* Consume and apply skip, if present (i.e. if MSB=0) */
@@ -275,7 +276,7 @@ apply_relocs_loop:
 1:	andi	t0, a3, 1
 	beqz	t0, 2f
 	LOADN	t1, (a1)
-	add	t1, t1, a0
+	add	t1, t1, a2
 	STOREN	t1, (a1)
 2:	addi	a1, a1, ( __riscv_xlen / 8 )
 	srli	a3, a3, 1

src/arch/riscv/prefix/sbiprefix.S

@@ -66,6 +66,7 @@ _sbi_start:
 	progress "\nSBI->iPXE"
 
 	/* Apply dynamic relocations */
+	la	a0, _edata
 	call	apply_relocs
 	progress " .reloc"