[PATCH v3 4/8] [ppc] Process dynamic relocations for kernel
Suzuki K. Poulose
suzuki at in.ibm.com
Mon Nov 14 16:43:04 EST 2011
The following patch implements the dynamic relocation processing for
PPC32 kernel. relocate() accepts the target virtual address and relocates
the kernel image to the same.
Currently the following relocation types are handled :
R_PPC_RELATIVE
R_PPC_ADDR16_LO
R_PPC_ADDR16_HI
R_PPC_ADDR16_HA
The last 3 relocations in the above list depends on value of Symbol indexed
whose index is encoded in the Relocation entry. Hence we need the Symbol
Table for processing such relocations.
Note: The GNU ld for ppc32 produces buggy relocations for relocation types
that depend on symbols. The value of the symbols with STB_LOCAL scope
should be assumed to be zero. - Alan Modra
Changes since v2:
* Flush the d-cache'd instructions and invalidate the i-cache to reflect
the processed instructions.(Reported by: Josh Poimboeuf)
Signed-off-by: Suzuki K. Poulose <suzuki at in.ibm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe at linux.vnet.ibm.com>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Alan Modra <amodra at au1.ibm.com>
Cc: Kumar Gala <galak at kernel.crashing.org>
Cc: linuxppc-dev <linuxppc-dev at lists.ozlabs.org>
---
arch/powerpc/Kconfig | 41 ++++---
arch/powerpc/Makefile | 6 +
arch/powerpc/kernel/Makefile | 2
arch/powerpc/kernel/reloc_32.S | 207 +++++++++++++++++++++++++++++++++++++
arch/powerpc/kernel/vmlinux.lds.S | 8 +
5 files changed, 243 insertions(+), 21 deletions(-)
create mode 100644 arch/powerpc/kernel/reloc_32.S
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 076782d..a976f75 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -855,23 +855,30 @@ config DYNAMIC_MEMSTART
load address. When this option is enabled, the compile time physical
address CONFIG_PHYSICAL_START is ignored.
-# Mapping based RELOCATABLE is moved to DYNAMIC_MEMSTART
-# config RELOCATABLE
-# bool "Build a relocatable kernel (EXPERIMENTAL)"
-# depends on EXPERIMENTAL && ADVANCED_OPTIONS && FLATMEM && (FSL_BOOKE || PPC_47x)
-# help
-# This builds a kernel image that is capable of running at the
-# location the kernel is loaded at, without any alignment restrictions.
-#
-# One use is for the kexec on panic case where the recovery kernel
-# must live at a different physical address than the primary
-# kernel.
-#
-# Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address
-# it has been loaded at and the compile time physical addresses
-# CONFIG_PHYSICAL_START is ignored. However CONFIG_PHYSICAL_START
-# setting can still be useful to bootwrappers that need to know the
-# load location of the kernel (eg. u-boot/mkimage).
+ This option is overridden by RELOCATABLE.
+
+config RELOCATABLE
+ bool "Build a relocatable kernel (EXPERIMENTAL)"
+ depends on EXPERIMENTAL && ADVANCED_OPTIONS && FLATMEM
+ help
+ This builds a kernel image that is capable of running at the
+ location the kernel is loaded at, without any alignment restrictions.
+ This feature is a superset of DYNAMIC_MEMSTART, and hence overrides
+ it.
+
+ One use is for the kexec on panic case where the recovery kernel
+ must live at a different physical address than the primary
+ kernel.
+
+ Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address
+ it has been loaded at and the compile time physical addresses
+ CONFIG_PHYSICAL_START is ignored. However CONFIG_PHYSICAL_START
+ setting can still be useful to bootwrappers that need to know the
+ load address of the kernel (eg. u-boot/mkimage).
+
+config RELOCATABLE_PPC32
+ def_bool y
+ depends on PPC32 && RELOCATABLE
config PAGE_OFFSET_BOOL
bool "Set custom page offset address"
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 57af16e..435ecb8 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -63,9 +63,9 @@ override CC += -m$(CONFIG_WORD_SIZE)
override AR := GNUTARGET=elf$(CONFIG_WORD_SIZE)-powerpc $(AR)
endif
-LDFLAGS_vmlinux-yy := -Bstatic
-LDFLAGS_vmlinux-$(CONFIG_PPC64)$(CONFIG_RELOCATABLE) := -pie
-LDFLAGS_vmlinux := $(LDFLAGS_vmlinux-yy)
+LDFLAGS_vmlinux-y := -Bstatic
+LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
+LDFLAGS_vmlinux := $(LDFLAGS_vmlinux-y)
CFLAGS-$(CONFIG_PPC64) := -mminimal-toc -mtraceback=no -mcall-aixdesc
CFLAGS-$(CONFIG_PPC32) := -ffixed-r2 -mmultiple
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index ce4f7f1..ee728e4 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -85,6 +85,8 @@ extra-$(CONFIG_FSL_BOOKE) := head_fsl_booke.o
extra-$(CONFIG_8xx) := head_8xx.o
extra-y += vmlinux.lds
+obj-$(CONFIG_RELOCATABLE_PPC32) += reloc_32.o
+
obj-$(CONFIG_PPC32) += entry_32.o setup_32.o
obj-$(CONFIG_PPC64) += dma-iommu.o iommu.o
obj-$(CONFIG_KGDB) += kgdb.o
diff --git a/arch/powerpc/kernel/reloc_32.S b/arch/powerpc/kernel/reloc_32.S
new file mode 100644
index 0000000..a45438e
--- /dev/null
+++ b/arch/powerpc/kernel/reloc_32.S
@@ -0,0 +1,207 @@
+/*
+ * Code to process dynamic relocations for PPC32.
+ *
+ * Copyrights (C) IBM Corporation, 2011.
+ * Author: Suzuki Poulose <suzuki at in.ibm.com>
+ *
+ * - Based on ppc64 code - reloc_64.S
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <asm/ppc_asm.h>
+
+/* Dynamic section table entry tags */
+DT_RELA = 7 /* Tag for Elf32_Rela section */
+DT_RELASZ = 8 /* Size of the Rela relocs */
+DT_RELAENT = 9 /* Size of one Rela reloc entry */
+
+STN_UNDEF = 0 /* Undefined symbol index */
+STB_LOCAL = 0 /* Local binding for the symbol */
+
+R_PPC_ADDR16_LO = 4 /* Lower half of (S+A) */
+R_PPC_ADDR16_HI = 5 /* Upper half of (S+A) */
+R_PPC_ADDR16_HA = 6 /* High Adjusted (S+A) */
+R_PPC_RELATIVE = 22
+
+/*
+ * r3 = desired final address
+ */
+
+_GLOBAL(relocate)
+
+ mflr r0 /* Save our LR */
+ bl 0f /* Find our current runtime address */
+0: mflr r12 /* Make it accessible */
+ mtlr r0
+
+ lwz r11, (p_dyn - 0b)(r12)
+ add r11, r11, r12 /* runtime address of .dynamic section */
+ lwz r9, (p_rela - 0b)(r12)
+ add r9, r9, r12 /* runtime address of .rela.dyn section */
+ lwz r10, (p_st - 0b)(r12)
+ add r10, r10, r12 /* runtime address of _stext section */
+ lwz r13, (p_sym - 0b)(r12)
+ add r13, r13, r12 /* runtime address of .dynsym section */
+
+ /*
+ * Scan the dynamic section for RELA, RELASZ entries
+ */
+ li r6, 0
+ li r7, 0
+ li r8, 0
+1: lwz r5, 0(r11) /* ELF_Dyn.d_tag */
+ cmpwi r5, 0 /* End of ELF_Dyn[] */
+ beq eodyn
+ cmpwi r5, DT_RELA
+ bne relasz
+ lwz r7, 4(r11) /* r7 = rela.link */
+ b skip
+relasz:
+ cmpwi r5, DT_RELASZ
+ bne relaent
+ lwz r8, 4(r11) /* r8 = Total Rela relocs size */
+ b skip
+relaent:
+ cmpwi r5, DT_RELAENT
+ bne skip
+ lwz r6, 4(r11) /* r6 = Size of one Rela reloc */
+skip:
+ addi r11, r11, 8
+ b 1b
+eodyn: /* End of Dyn Table scan */
+
+ /* Check if we have found all the entries */
+ cmpwi r7, 0
+ beq done
+ cmpwi r8, 0
+ beq done
+ cmpwi r6, 0
+ beq done
+
+
+ /*
+ * Work out the current offset from the link time address of .rela
+ * section.
+ * cur_offset[r7] = rela.run[r9] - rela.link [r7]
+ * _stext.link[r12] = _stext.run[r10] - cur_offset[r7]
+ * final_offset[r3] = _stext.final[r3] - _stext.link[r12]
+ */
+ subf r7, r7, r9 /* cur_offset */
+ subf r12, r7, r10
+ subf r3, r12, r3 /* final_offset */
+
+ subf r8, r6, r8 /* relaz -= relaent */
+ /*
+ * Scan through the .rela table and process each entry
+ * r9 - points to the current .rela table entry
+ * r13 - points to the symbol table
+ */
+
+ /*
+ * Check if we have a relocation based on symbol
+ * r5 will hold the value of the symbol.
+ */
+applyrela:
+ lwz r4, 4(r9)
+ srwi r5, r4, 8 /* ELF32_R_SYM(r_info) */
+ cmpwi r5, STN_UNDEF /* sym == STN_UNDEF ? */
+ beq get_type /* value = 0 */
+ /* Find the value of the symbol at index(r5) */
+ slwi r5, r5, 4 /* r5 = r5 * sizeof(Elf32_Sym) */
+ add r12, r13, r5 /* r12 = &__dyn_sym[Index] */
+
+ /*
+ * GNU ld has a bug, where dynamic relocs based on
+ * STB_LOCAL symbols, the value should be assumed
+ * to be zero. - Alan Modra
+ */
+ /* XXX: Do we need to check if we are using GNU ld ? */
+ lbz r5, 12(r12) /* r5 = dyn_sym[Index].st_info */
+ extrwi r5, r5, 4, 24 /* r5 = ELF32_ST_BIND(r5) */
+ cmpwi r5, STB_LOCAL /* st_value = 0, ld bug */
+ beq get_type /* We have r5 = 0 */
+ lwz r5, 4(r12) /* r5 = __dyn_sym[Index].st_value */
+
+get_type:
+ /* r4 holds the relocation type */
+ extrwi r4, r4, 8, 24 /* r4 = ((char*)r4)[3] */
+
+ /* R_PPC_RELATIVE */
+ cmpwi r4, R_PPC_RELATIVE
+ bne hi16
+ lwz r4, 0(r9) /* r_offset */
+ lwz r0, 8(r9) /* r_addend */
+ add r0, r0, r3 /* final addend */
+ stwx r0, r4, r7 /* memory[r4+r7]) = (u32)r0 */
+ b nxtrela /* continue */
+
+ /* R_PPC_ADDR16_HI */
+hi16:
+ cmpwi r4, R_PPC_ADDR16_HI
+ bne ha16
+ lwz r4, 0(r9) /* r_offset */
+ lwz r0, 8(r9) /* r_addend */
+ add r0, r0, r3
+ add r0, r0, r5 /* r0 = (S+A+Offset) */
+ extrwi r0, r0, 16, 0 /* r0 = (r0 >> 16) */
+ b store_half
+
+ /* R_PPC_ADDR16_HA */
+ha16:
+ cmpwi r4, R_PPC_ADDR16_HA
+ bne lo16
+ lwz r4, 0(r9) /* r_offset */
+ lwz r0, 8(r9) /* r_addend */
+ add r0, r0, r3
+ add r0, r0, r5 /* r0 = (S+A+Offset) */
+ extrwi r5, r0, 1, 16 /* Extract bit 16 */
+ extrwi r0, r0, 16, 0 /* r0 = (r0 >> 16) */
+ add r0, r0, r5 /* Add it to r0 */
+ b store_half
+
+ /* R_PPC_ADDR16_LO */
+lo16:
+ cmpwi r4, R_PPC_ADDR16_LO
+ bne nxtrela
+ lwz r4, 0(r9) /* r_offset */
+ lwz r0, 8(r9) /* r_addend */
+ add r0, r0, r3
+ add r0, r0, r5 /* r0 = (S+A+Offset) */
+ extrwi r0, r0, 16, 16 /* r0 &= 0xffff */
+ /* Fall through to */
+
+ /* Store half word */
+store_half:
+ sthx r0, r4, r7 /* memory[r4+r7] = (u16)r0 */
+
+nxtrela:
+ /*
+ * We have to flush the modified instructions to the
+ * main storage from the d-cache. And also, invalidate the
+ * cached instructions in i-cache which has been modified.
+ *
+ * We delay the msync / isync operation till the end, since
+ * we won't be executing the modified instructions until
+ * we return from here.
+ */
+ dcbst r4,r7
+ icbi r4,r7
+ cmpwi r8, 0 /* relasz = 0 ? */
+ ble done
+ add r9, r9, r6 /* move to next entry in the .rela table */
+ subf r8, r6, r8 /* relasz -= relaent */
+ b applyrela
+
+done:
+ msync /* Wait for the flush to finish */
+ isync /* Discard prefetched instructions */
+ blr
+
+p_dyn: .long __dynamic_start - 0b
+p_rela: .long __rela_dyn_start - 0b
+p_sym: .long __dynamic_symtab - 0b
+p_st: .long _stext - 0b
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 920276c..710a540 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -170,7 +170,13 @@ SECTIONS
}
#ifdef CONFIG_RELOCATABLE
. = ALIGN(8);
- .dynsym : AT(ADDR(.dynsym) - LOAD_OFFSET) { *(.dynsym) }
+ .dynsym : AT(ADDR(.dynsym) - LOAD_OFFSET)
+ {
+#ifdef CONFIG_RELOCATABLE_PPC32
+ __dynamic_symtab = .;
+#endif
+ *(.dynsym)
+ }
.dynstr : AT(ADDR(.dynstr) - LOAD_OFFSET) { *(.dynstr) }
.dynamic : AT(ADDR(.dynamic) - LOAD_OFFSET)
{
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