[PATCH] RISC-V: Fix VDSO build for !MMU

[Palmer Dabbelt <palmer@dabbelt.com>]

From: Palmer Dabbelt <palmerdabbelt@google.com>

We don't have a VDSO for the !MMU configurations, so don't try to build
one.

Fixes: fde9c59aebaf ("riscv: explicitly use symbol offsets for VDSO")
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
 arch/riscv/Makefile           | 2 ++
 arch/riscv/include/asm/vdso.h | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index e026b2d0a5a4..83ee0e71204c 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -108,9 +108,11 @@ PHONY += vdso_install
 vdso_install:
 	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
 
+ifeq ($(CONFIG_MMU),y)
 prepare: vdso_prepare
 vdso_prepare: prepare0
 	$(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso include/generated/vdso-offsets.h
+endif
 
 ifneq ($(CONFIG_XIP_KERNEL),y)
 ifeq ($(CONFIG_RISCV_M_MODE)$(CONFIG_SOC_CANAAN),yy)
diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index d8d003c2b5a3..893e47195e30 100644
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -8,6 +8,13 @@
 #ifndef _ASM_RISCV_VDSO_H
 #define _ASM_RISCV_VDSO_H
 
+
+/*
+ * All systems with an MMU have a VDSO, but systems without an MMU don't
+ * support shared libraries and therefor don't have one.
+ */
+#ifdef CONFIG_MMU
+
 #include <linux/types.h>
 #include <generated/vdso-offsets.h>
 
@@ -19,6 +26,8 @@ struct vdso_data {
 #define VDSO_SYMBOL(base, name)							\
 	(void __user *)((unsigned long)(base) + __vdso_##name##_offset)
 
+#endif /* CONFIG_MMU */
+
 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
 
 #endif /* _ASM_RISCV_VDSO_H */
-- 
2.33.0.259.gc128427fd7-goog