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From: Linus Walleij <linus.walleij@linaro.org>
To: linux-arm-kernel@lists.infradead.org,
	Russell King <linux@armlinux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Ard Biesheuvel <ardb@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: [PATCH 1/3] ARM: Split KERNEL_OFFSET from PAGE_OFFSET
Date: Mon, 17 May 2021 16:57:17 +0200	[thread overview]
Message-ID: <20210517145719.110966-2-linus.walleij@linaro.org> (raw)
In-Reply-To: <20210517145719.110966-1-linus.walleij@linaro.org>

We want to be able to compile the kernel into an address different
from PAGE_OFFSET (start of lowmem) + TEXT_OFFSET, so start to pry
apart the address of where the kernel is located from the address
where the lowmem is located by defining and using KERNEL_OFFSET in
a few key places.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 arch/arm/include/asm/memory.h | 8 +++++++-
 arch/arm/kernel/head.S        | 3 +--
 arch/arm/kernel/vmlinux.lds.S | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index a711322d9f40..a5f1d1826a98 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -20,8 +20,14 @@
 #endif
 #include <asm/kasan_def.h>
 
-/* PAGE_OFFSET - the virtual address of the start of the kernel image */
+/*
+ * PAGE_OFFSET: the virtual address of the start of lowmem, memory above
+ *   the virtual address range for userspace.
+ * KERNEL_OFFSET: the virtual address of the start of the kernel image.
+ *   we may further offset this with TEXT_OFFSET in practice.
+ */
 #define PAGE_OFFSET		UL(CONFIG_PAGE_OFFSET)
+#define KERNEL_OFFSET		(PAGE_OFFSET)
 
 #ifdef CONFIG_MMU
 
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 7f62c5eccdf3..4e2daaa7636a 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -23,7 +23,6 @@
 #if defined(CONFIG_DEBUG_LL) && !defined(CONFIG_DEBUG_SEMIHOSTING)
 #include CONFIG_DEBUG_LL_INCLUDE
 #endif
-
 /*
  * swapper_pg_dir is the virtual address of the initial page table.
  * We place the page tables 16K below KERNEL_RAM_VADDR.  Therefore, we must
@@ -31,7 +30,7 @@
  * the least significant 16 bits to be 0x8000, but we could probably
  * relax this restriction to KERNEL_RAM_VADDR >= PAGE_OFFSET + 0x4000.
  */
-#define KERNEL_RAM_VADDR	(PAGE_OFFSET + TEXT_OFFSET)
+#define KERNEL_RAM_VADDR	(KERNEL_OFFSET + TEXT_OFFSET)
 #if (KERNEL_RAM_VADDR & 0xffff) != 0x8000
 #error KERNEL_RAM_VADDR must start at 0xXXXX8000
 #endif
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index f7f4620d59c3..20c4f6d20c7a 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -47,7 +47,7 @@ SECTIONS
 #endif
 	}
 
-	. = PAGE_OFFSET + TEXT_OFFSET;
+	. = KERNEL_OFFSET + TEXT_OFFSET;
 	.head.text : {
 		_text = .;
 		HEAD_TEXT
-- 
2.31.1


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  reply	other threads:[~2021-05-17 15:02 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-17 14:57 [PATCH 0/3] Split lowmem and kernel mappings Linus Walleij
2021-05-17 14:57 ` Linus Walleij [this message]
2021-05-17 14:57 ` [PATCH 2/3] ARM: Define kernel physical section start and end Linus Walleij
2021-05-17 14:57 ` [PATCH 3/3] ARM: Map the lowmem and kernel separately Linus Walleij
2021-07-30 20:22   ` Nishanth Menon
2021-07-30 22:40     ` Linus Walleij
2021-08-03 10:27       ` Grygorii Strashko
2021-08-03 10:49         ` Russell King (Oracle)
2021-08-03 11:34           ` Linus Walleij
2021-08-04 10:05           ` Linus Walleij
2021-08-04 10:36             ` Russell King (Oracle)
2021-08-04 13:12               ` Linus Walleij

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