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[RFT,v2,13/23] x86/linkage: Add SYM_PIC_ALIAS() macro helper to emit symbol aliases

Message ID 20250504095230.2932860-38-ardb+git@google.com
State New
Headers show
Series x86: strict separation of startup code | expand

Commit Message

Ard Biesheuvel May 4, 2025, 9:52 a.m. UTC 
From: Ard Biesheuvel <ardb@kernel.org>

Startup code that may execute from the early 1:1 mapping of memory will
be confined into its own address space, and only be permitted to access
ordinary kernel symbols if this is known to be safe.

Introduce a macro helper SYM_PIC_ALIAS() that emits a __pi_ prefixed
alias for a symbol, which allows startup code to access it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/include/asm/linkage.h | 10 ++++++++++
 1 file changed, 10 insertions(+)
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Patch

diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h
index b51d8a4673f5..9d38ae744a2e 100644
--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -141,5 +141,15 @@ 
 #define SYM_FUNC_START_WEAK_NOALIGN(name)		\
 	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)
 
+/*
+ * Expose 'sym' to the startup code in arch/x86/boot/startup/, by emitting an
+ * alias prefixed with __pi_
+ */
+#ifdef __ASSEMBLER__
+#define SYM_PIC_ALIAS(sym)	SYM_ALIAS(__pi_ ## sym, sym, SYM_L_GLOBAL)
+#else
+#define SYM_PIC_ALIAS(sym)	extern typeof(sym) __PASTE(__pi_, sym) __alias(sym)
+#endif
+
 #endif /* _ASM_X86_LINKAGE_H */