Thread (19 messages) 19 messages, 4 authors, 2011-11-11

[PATCH v2 3/5] [44x] Enable CONFIG_RELOCATABLE for PPC44x

From: Suzuki K. Poulose <hidden>
Date: 2011-10-25 11:54:26
Subsystem: linux for powerpc (32-bit and 64-bit), the rest · Maintainers: Madhavan Srinivasan, Michael Ellerman, Linus Torvalds

The following patch adds relocatable support for PPC44x kernel.

This enables two types of relocatable kernel support for PPC44x.

1) The old style, mapping based- which restricts the load address to 256M
   aligned.

2) The new approach based on processing dynamic relocation entries -
   CONFIG_RELOCATABLE_PPC32_PIE


In case of CONFIG_RELOCATABLE_PPC32_PIE :

We find the runtime address of _stext and relocate ourselves based
on the following calculation.

	virtual_base = ALIGN(KERNELBASE,256M) +
			MODULO(_stext.run,256M)

relocate() is called with the Effective Virtual Base Address (as
shown below)

            | Phys. Addr| Virt. Addr |
Page (256M) |------------------------|
Boundary    |           |            |
            |           |            |
            |           |            |
Kernel Load |___________|_ __ _ _ _ _|<- Effective
Addr(_stext)|           |      ^     |Virt. Base Addr
            |           |      |     |
            |           |      |     |
            |           |reloc_offset|
            |           |      |     |
            |           |      |     |
            |           |______v_____|<-(KERNELBASE)%256M
            |           |            |
            |           |            |
            |           |            |
Page(256M)  |-----------|------------|
Boundary    |           |            |

The virt_phys_offset is updated accordingly, i.e,

	virt_phys_offset = effective. kernel virt base - kernstart_addr

I have tested the patches on 440x platforms only. However this should
work fine for PPC_47x also, as we only depend on the runtime address
and the current TLB XLAT entry for the startup code, which is available
in r25. I don't have access to a 47x board yet. So, it would be great if
somebody could test this on 47x.

Signed-off-by: Suzuki K. Poulose <redacted>
Cc:	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:	Kumar Gala <redacted>
Cc:	Tony Breeds <redacted>
Cc:	Josh Boyer <redacted>
Cc:	linuxppc-dev <redacted>
---

 arch/powerpc/Kconfig           |    4 +
 arch/powerpc/kernel/head_44x.S |  110 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 108 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 016f863..1cedcda 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -843,7 +843,7 @@ config LOWMEM_CAM_NUM
 
 config RELOCATABLE
 	bool "Build a relocatable kernel (EXPERIMENTAL)"
-	depends on EXPERIMENTAL && ADVANCED_OPTIONS && FLATMEM && (FSL_BOOKE || PPC_47x)
+	depends on EXPERIMENTAL && ADVANCED_OPTIONS && FLATMEM && (FSL_BOOKE || 44x)
 	help
 	  This builds a kernel image that is capable of running at the
 	  location the kernel is loaded at (some alignment restrictions may
@@ -862,7 +862,7 @@ config RELOCATABLE
 config RELOCATABLE_PPC32_PIE
 	bool "Compile the kernel with dynamic relocations (EXPERIMENTAL)"
 	default n
-	depends on PPC32 && RELOCATABLE
+	depends on PPC32 && RELOCATABLE && 44x
 	help
 	  This option builds the kernel with dynamic relocations(-pie). Enables
 	  the kernel to be loaded at any address for BOOKE processors, removing
diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index b725dab..213759e 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -64,6 +64,35 @@ _ENTRY(_start);
 	mr	r31,r3		/* save device tree ptr */
 	li	r24,0		/* CPU number */
 
+#ifdef CONFIG_RELOCATABLE_PPC32_PIE
+/*
+ * Relocate ourselves to the current runtime address.
+ * This is called only by the Boot CPU.
+ * "relocate" is called with our current runtime virutal
+ * address.
+ * r21 will be loaded with the physical runtime address of _stext
+ */
+	bl	0f				/* Get our runtime address */
+0:	mflr	r21				/* Make it accessible */
+	addis	r21,r21,(_stext - 0b)@ha
+	addi	r21,r21,(_stext - 0b)@l 	/* Get our current runtime base */
+
+	/*
+	 * We have the runtime (virutal) address of our base.
+	 * We calculate our shift of offset from a 256M page.
+	 * We could map the 256M page we belong to at PAGE_OFFSET and
+	 * get going from there.
+	 */
+	lis	r4,KERNELBASE@h
+	ori	r4,r4,KERNELBASE@l
+	rlwinm	r6,r21,0,4,31			/* r6 = PHYS_START % 256M */
+	rlwinm	r5,r4,0,4,31			/* r5 = KERNELBASE % 256M */
+	subf	r3,r5,r6			/* r3 = r6 - r5 */
+	add	r3,r4,r3			/* Required Virutal Address */
+
+	bl	relocate
+#endif
+
 	bl	init_cpu_state
 
 	/*
@@ -88,14 +117,66 @@ _ENTRY(_start);
 
 #ifdef CONFIG_RELOCATABLE
 	/*
+	 * When we reach here :
 	 * r25 will contain RPN/ERPN for the start address of memory
-	 *
-	 * Add the difference between KERNELBASE and PAGE_OFFSET to the
-	 * start of physical memory to get kernstart_addr.
+	 * r21 contain the physical address of _stext in case of PIE
 	 */
 	lis	r3,kernstart_addr@ha
 	la	r3,kernstart_addr@l(r3)
 
+#ifdef CONFIG_RELOCATABLE_PPC32_PIE
+	/*
+	 * Compute the kernstart_addr.
+	 * kernstart_addr => (r6,r8)
+	 * kernstart_addr & ~0xfffffff => (r6,r7)
+	 */
+	rlwinm	r6,r25,0,28,31	/* ERPN. Bits 32-35 of Address */
+	rlwinm	r7,r25,0,0,3	/* RPN - assuming 256 MB page size */
+	rlwinm	r8,r21,0,4,31	/* r8 = (_stext & 0xfffffff) */
+	or	r8,r7,r8	/* Compute the lower 32bit of kernstart_addr */
+
+	/* Store kernstart_addr */
+	stw	r6,0(r3)	/* higher 32bit */
+	stw	r8,4(r3)	/* lower 32bit  */
+
+	/*
+	 * Compute the virt_phys_offset :
+	 * virt_phys_offset = stext.run - kernstart_addr
+	 *
+	 * stext.run = (KERNELBASE & ~0xfffffff) + (kernstart_addr & 0xfffffff)
+	 * When we relocate, we have :
+	 *
+	 *	(kernstart_addr & 0xfffffff) = (stext.run & 0xfffffff)
+	 *
+	 * hence:
+	 *  virt_phys_offset = (KERNELBASE & ~0xfffffff) - (kernstart_addr & ~0xfffffff)
+	 *
+	 */
+
+	/* KERNELBASE&~0xfffffff => (r4,r5) */
+	li	r4, 0		/* higer 32bit */
+	lis	r5,KERNELBASE@h
+	rlwinm	r5,r5,0,0,3	/* Align to 256M, lower 32bit */
+
+	/*
+	 * 64bit subtraction.
+	 */
+	subfc	r5,r7,r5
+	subfe	r4,r6,r4
+
+	/* Store virt_phys_offset */
+	lis	r3,virt_phys_offset@ha
+	la	r3,virt_phys_offset@l(r3)
+
+	stw	r4,0(r3)
+	stw	r5,4(r3)
+#else
+	/* Old style mapping based relocation */
+
+	/*
+	 * Add the difference between KERNELBASE and PAGE_OFFSET to the
+	 * start of physical memory to get kernstart_addr.
+	 */
 	lis	r4,KERNELBASE@h
 	ori	r4,r4,KERNELBASE@l
 	lis	r5,PAGE_OFFSET@h
@@ -108,7 +189,9 @@ _ENTRY(_start);
 
 	stw	r6,0(r3)
 	stw	r7,4(r3)
-#endif
+#endif	/* CONFIG_RELOCATABLE_PPC32_PIE */
+
+#endif /* CONFIG_RELOCATABLE */
 
 /*
  * Decide what sort of machine this is and initialize the MMU.
@@ -801,11 +884,30 @@ skpinv:	addi	r4,r4,1				/* Increment */
  * Configure and load pinned entry into TLB slot 63.
  */
 
+#ifdef CONFIG_RELOCATABLE
+	/*
+	 * Stores the XLAT entry for this code at r25.
+	 * Uses the mapping where we are loaded.
+	 */
+
+	tlbre	r25,r23,PPC44x_TLB_XLAT		/* Read our XLAT entry in r25 */
+
+	/* PAGEID fields for mapping */
+	lis	r3,KERNELBASE@h
+	rlwinm	r3,r3,0,0,3			/* Round to 256M page boundary */
+
+	/* Use the current XLAT entry */
+	mr	r4,r25
+#else
+
+
 	lis	r3,PAGE_OFFSET@h
 	ori	r3,r3,PAGE_OFFSET@l
 
 	/* Kernel is at the base of RAM */
 	li r4, 0			/* Load the kernel physical address */
+#endif
+
 
 	/* Load the kernel PID = 0 */
 	li	r0,0
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