[RFC 4/5] ARM: P2V: introduce phys_to_virt/virt_to_phys runtime patching
From: Jamie Iles <hidden>
Date: 2011-02-09 12:17:01
Subsystem:
arm port, the rest · Maintainers:
Russell King, Linus Torvalds
Hi Russell, I haven't been using the runtime patching, but building picoxcell based off of todays next I'm seeing a pretty harmless warning. Fixup below. Jamie On Tue, Jan 04, 2011 at 08:23:18PM +0000, Russell King - ARM Linux wrote:
This idea came from Nicolas, Eric Miao produced an initial version, which was then rewritten into this. Patch the physical to virtual translations at runtime. As we modify the code, this makes it incompatible with XIP kernels, but on allows is to achieve this with minimal loss of performance. As many translations are of the form: physical = virtual + (PHYS_OFFSET - PAGE_OFFSET) virtual = physical - (PHYS_OFFSET - PAGE_OFFSET) we generate an 'add' instruction for __virt_to_phys(), and a 'sub' instruction for __phys_to_virt(). We calculate at run time (PHYS_OFFSET - PAGE_OFFSET) by comparing the address prior to MMU initialization with where it should be once the MMU has been initialized, and place this constant into the above add/sub instructions. Once we have (PHYS_OFFSET - PAGE_OFFSET), we can calcuate the real PHYS_OFFSET as PAGE_OFFSET is a build-time constant, and save this for the C-mode PHYS_OFFSET variable definition to use. At present, we are unable to support Realview with Sparsemem enabled as this uses a complex mapping function, and MSM as this requires a constant which will not fit in our math instruction. Signed-off-by: Russell King <redacted> --- arch/arm/Kconfig | 14 +++++++++ arch/arm/include/asm/memory.h | 55 ++++++++++++++++++++++++++++-------- arch/arm/kernel/head.S | 63 +++++++++++++++++++++++++++++++++++++++++ arch/arm/kernel/module.c | 23 ++++++++++++++- arch/arm/kernel/setup.c | 2 +- arch/arm/kernel/vmlinux.lds.S | 4 ++ 6 files changed, 147 insertions(+), 14 deletions(-)
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quoted hunk ↗ jump to hunk
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c index 0c1bb68..6a42e17 100644 --- a/arch/arm/kernel/module.c +++ b/arch/arm/kernel/module.c@@ -276,12 +276,28 @@ struct mod_unwind_map { const Elf_Shdr *txt_sec; }; +static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr, + const Elf_Shdr *sechdrs, const char *name) +{ + const Elf_Shdr *s, *se; + const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; + + for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++) + if (strcmp(name, secstrs + s->sh_name) == 0) + return s; + + return NULL; +} + +extern void fixup_pv_table(const void *, unsigned long); + int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs, struct module *mod) { + const Elf_Shdr *s = NULL; #ifdef CONFIG_ARM_UNWIND const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; - const Elf_Shdr *s, *sechdrs_end = sechdrs + hdr->e_shnum; + const Elf_Shdr *sechdrs_end = sechdrs + hdr->e_shnum; struct mod_unwind_map maps[ARM_SEC_MAX]; int i;@@ -323,6 +339,11 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs, maps[i].txt_sec->sh_addr, maps[i].txt_sec->sh_size); #endif +#ifdef CONFIG_ARM_PATCH_PHYS_VIRT + s = find_mod_section(hdr, sechdrs, ".pv_table"); + if (s) + fixup_pv_table((void *)s->sh_addr, s->sh_size); +#endif
If we don't have CONFIG_ARM_PATCH_PHYS_VIRT defined then we get: arch/arm/kernel/module.c:272: warning: ?find_mod_section? defined but not used 8<------
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index 74e25ab..ba65805 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c@@ -269,6 +269,7 @@ struct mod_unwind_map { const Elf_Shdr *txt_sec; }; +#ifdef CONFIG_ARM_PATCH_PHYS_VIRT static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs, const char *name) {
@@ -281,6 +282,7 @@ static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr, return NULL; } +#endif extern void fixup_pv_table(const void *, unsigned long);