linux-kernel - [PATCH v2 3/8] KVM: arm64: Add symbol at the beginning of each hyp section

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Message-Id: <20210105180541.65031-4-dbrazdil@google.com>
Date:   Tue,  5 Jan 2021 18:05:36 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     kvmarm@...ts.cs.columbia.edu
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Brazdil <dbrazdil@...gle.com>
Subject: [PATCH v2 3/8] KVM: arm64: Add symbol at the beginning of each hyp section

Generating hyp relocations will require referencing positions at a given
offset from the beginning of hyp sections. Since the final layout will
not be determined until the linking of `vmlinux`, modify the hyp linker
script to insert a symbol at the first byte of each hyp section to use
as an anchor. The linker of `vmlinux` will place the symbols together
with the sections.

Signed-off-by: David Brazdil <dbrazdil@...gle.com>
---
 arch/arm64/include/asm/hyp_image.h | 29 +++++++++++++++++++++++++++--
 arch/arm64/kvm/hyp/nvhe/hyp.lds.S  |  4 ++--
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/hyp_image.h b/arch/arm64/include/asm/hyp_image.h
index daa1a1da539e..f97b774b58f4 100644
--- a/arch/arm64/include/asm/hyp_image.h
+++ b/arch/arm64/include/asm/hyp_image.h
@@ -7,6 +7,9 @@
 #ifndef __ARM64_HYP_IMAGE_H__
 #define __ARM64_HYP_IMAGE_H__
 
+#define HYP_CONCAT(a, b)	__HYP_CONCAT(a, b)
+#define __HYP_CONCAT(a, b)	a ## b
+
 /*
  * KVM nVHE code has its own symbol namespace prefixed with __kvm_nvhe_,
  * to separate it from the kernel proper.
@@ -21,9 +24,31 @@
  */
 #define HYP_SECTION_NAME(NAME)	.hyp##NAME
 
+/* Symbol defined at the beginning of each hyp section. */
+#define HYP_SECTION_SYMBOL_NAME(NAME) \
+	HYP_CONCAT(__hyp_section_, HYP_SECTION_NAME(NAME))
+
+/*
+ * Helper to generate linker script statements starting a hyp section.
+ *
+ * A symbol with a well-known name is defined at the first byte. This
+ * is used as a base for hyp relocations (see gen-hyprel.c). It must
+ * be defined inside the section so the linker of `vmlinux` cannot
+ * separate it from the section data.
+ */
+#define BEGIN_HYP_SECTION(NAME)				\
+	HYP_SECTION_NAME(NAME) : {			\
+		HYP_SECTION_SYMBOL_NAME(NAME) = .;
+
+/* Helper to generate linker script statements ending a hyp section. */
+#define END_HYP_SECTION					\
+	}
+
 /* Defines an ELF hyp section from input section @NAME and its subsections. */
-#define HYP_SECTION(NAME) \
-	HYP_SECTION_NAME(NAME) : { *(NAME NAME##.*) }
+#define HYP_SECTION(NAME)			\
+	BEGIN_HYP_SECTION(NAME)			\
+		*(NAME NAME##.*)		\
+	END_HYP_SECTION
 
 /*
  * Defines a linker script alias of a kernel-proper symbol referenced by
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index cfdc59b4329b..cd119d82d8e3 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -22,7 +22,7 @@ SECTIONS {
 	 * alignment for when linking into vmlinux.
 	 */
 	. = ALIGN(PAGE_SIZE);
-	HYP_SECTION_NAME(.data..percpu) : {
+	BEGIN_HYP_SECTION(.data..percpu)
 		PERCPU_INPUT(L1_CACHE_BYTES)
-	}
+	END_HYP_SECTION
 }
-- 
2.29.2.729.g45daf8777d-goog