Add support for 64-bit PowerPC kernels to be directly loaded by kexec, which

is used as the bootloader on a number of PPC64 platforms. This involves the
following pieces:
- Making the first instruction a valid kernel entry point, since kexec
  ignores the ELF entry value. This requires a separate section and linker
  magic to prevent the linker from filling the beginning of the section
  with stubs.
- Adding an entry point at 0x60 past the first instruction for systems
  lacking firmware CPU shutdown support (notably PS3).
- Linker script changes to support the above.

MFC after:	1 month

sys/conf/ldscript.powerpc64

@@ -8,8 +8,12 @@ SEARCH_DIR(/usr/lib);
 PROVIDE (__stack = 0);
 SECTIONS
 {
-  /* Read-only sections, merged into text segment: */
 
+  /* Low-address wrapper for bootloaders (kexec/kboot) that can't parse ELF */
+  . = kernbase - 0x100;
+  .kboot : { *(.text.kboot) }
+
+  /* Read-only sections, merged into text segment: */
   . = kernbase;
   PROVIDE (begin = .);
 
@@ -28,6 +32,9 @@ SECTIONS
   .interpX    : { *(.interp) 	} : NONE
   /DISCARD/   : { *(.interp)	} 
 
+  /* Also delete notes */
+  /DISCARD/   : { *(.note.*)	} 
+
   .hash          : { *(.hash)		}
   .dynsym        : { *(.dynsym)		}
   .dynstr        : { *(.dynstr)		}

sys/powerpc/aim/locore64.S

@@ -61,6 +61,47 @@ GLOBAL(tmpstk)
 
 TOC_ENTRY(tmpstk)
 
+/*
+ * Entry point for bootloaders that do not fully implement ELF and start
+ * at the beginning of the image (kexec, notably). In its own section so
+ * that it ends up before any linker-generated call stubs and actually at
+ * the beginning of the image. kexec on some systems also enters at
+ * (start of image) + 0x60, so put a spin loop there.
+ */
+	.section ".text.kboot", "x", @progbits
+kbootentry:
+	b __start
+. = kbootentry + 0x40	/* Magic address used in platform layer */
+	.global smp_spin_sem
+ap_kexec_spin_sem:
+	.long   -1
+. = kbootentry + 0x60	/* Entry point for kexec APs */
+ap_kexec_start:		/* At 0x60 past start, copied to 0x60 by kexec */
+	/* r3 set to CPU ID by kexec */
+
+	/* Invalidate icache for low-memory copy and jump there */
+	li	%r0,0x80
+	dcbst	0,%r0
+	sync
+	icbi	0,%r0
+	isync
+	ba	0x78			/* Absolute branch to next inst */
+
+1:	or	31,31,31		/* yield */
+	sync
+	lwz	%r1,0x40(0)		/* Spin on ap_kexec_spin_sem */
+	cmpw	%r1,%r3			/* Until it equals our CPU ID */
+	bne	1b
+	
+	/* Released */
+	or	2,2,2			/* unyield */
+	ba	EXC_RST
+
+
+/*
+ * Now start the real text section
+ */
+
 	.text
 	.globl	btext
 btext:

sys/powerpc/include/vmparam.h

@@ -108,7 +108,7 @@
 #endif
 
 #ifdef AIM
-#define	KERNBASE		0x00100000UL	/* start of kernel virtual */
+#define	KERNBASE		0x00100100UL	/* start of kernel virtual */
 
 #ifndef __powerpc64__
 #define	VM_MIN_KERNEL_ADDRESS	((vm_offset_t)KERNEL_SR << ADDR_SR_SHFT)