[PATCH v2 1/7] riscv: Add kexec trampoline text section to vmlinux.lds.S

[fangyu.yu@linux.alibaba.com]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

When CONFIG_KEXEC_CORE is enabled, add a dedicated .kexec.tramp.text
area to the RISC-V kernel linker script.

This introduces a KEXEC_TRAMP_TEXT linker snippet in image-vars.h and
uses it from vmlinux.lds.S to:
  - align both the start and the end to PAGE_SIZE
  - define __kexec_tramp_text_start/__kexec_tramp_text_end
  - KEEP all .kexec.tramp.text* input sections
  - ASSERT the trampoline text fits within one page

The end-of-section page alignment guarantees that the trampoline page,
which is later identity-mapped as PAGE_KERNEL_EXEC, contains nothing but
the trampoline code and padding (no shared neighbour data).

When kexec is disabled, KEXEC_TRAMP_TEXT expands to nothing.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
 arch/riscv/kernel/image-vars.h  | 14 ++++++++++++++
 arch/riscv/kernel/vmlinux.lds.S |  1 +
 2 files changed, 15 insertions(+)

diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
index 3bd9d06a8b8f..35ee3f059afa 100644
--- a/arch/riscv/kernel/image-vars.h
+++ b/arch/riscv/kernel/image-vars.h
@@ -34,4 +34,18 @@ __efistub_sysfb_primary_display	= sysfb_primary_display;
 
 #endif
 
+#ifdef CONFIG_KEXEC_CORE
+#define KEXEC_TRAMP_TEXT						\
+		. = ALIGN(PAGE_SIZE);					\
+		__kexec_tramp_text_start = .;				\
+		KEEP(*(.kexec.tramp.text))				\
+		KEEP(*(.kexec.tramp.text.*))				\
+		__kexec_tramp_text_end = .;				\
+		ASSERT((__kexec_tramp_text_end - __kexec_tramp_text_start) <= PAGE_SIZE,  \
+			".kexec.tramp.text exceeds 4K");				\
+		. = ALIGN(PAGE_SIZE);
+#else
+#define KEXEC_TRAMP_TEXT /* nothing */
+#endif
+
 #endif /* __RISCV_KERNEL_IMAGE_VARS_H */
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 1f4f8496941a..fc7758e5b819 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -41,6 +41,7 @@ SECTIONS
 		ENTRY_TEXT
 		IRQENTRY_TEXT
 		SOFTIRQENTRY_TEXT
+		KEXEC_TRAMP_TEXT
 		_etext = .;
 	}
 
-- 
2.50.1