[PATCH v1 4/8] xen/riscv: introduce function for physical offset calculation

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

The function was introduced to not calculate and save physical
offset before MMU is enabled because access to start() is
PC-relative and in case of linker_addr != load_addr it will result
in incorrect value in phys_offset.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/riscv/include/asm/mm.h |  2 ++
 xen/arch/riscv/mm.c             | 18 +++++++++++++++---
 xen/arch/riscv/riscv64/head.S   |  2 ++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 64293eacee..996041ce81 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -11,4 +11,6 @@ void setup_initial_pagetables(void);
 void enable_mmu(void);
 void cont_after_mmu_is_enabled(void);
 
+void calc_phys_offset(void);
+
 #endif /* _ASM_RISCV_MM_H */
diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index 8ceed445cf..c092897f9a 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -19,9 +19,11 @@ struct mmu_desc {
 
 extern unsigned char cpu0_boot_stack[STACK_SIZE];
 
-#define PHYS_OFFSET ((unsigned long)_start - XEN_VIRT_START)
-#define LOAD_TO_LINK(addr) ((addr) - PHYS_OFFSET)
-#define LINK_TO_LOAD(addr) ((addr) + PHYS_OFFSET)
+static unsigned long phys_offset;
+
+#define LOAD_TO_LINK(addr) ((unsigned long)(addr) - phys_offset)
+#define LINK_TO_LOAD(addr) ((unsigned long)(addr) + phys_offset)
+
 
 /*
  * It is expected that Xen won't be more then 2 MB.
@@ -273,3 +275,13 @@ void __init noreturn noinline enable_mmu()
     switch_stack_and_jump((unsigned long)cpu0_boot_stack + STACK_SIZE,
                           cont_after_mmu_is_enabled);
 }
+
+/*
+ * calc_phys_offset() should be used before MMU is enabled because access to
+ * start() is PC-relative and in case when load_addr != linker_addr phys_offset
+ * will have an incorrect value
+ */
+void  calc_phys_offset(void)
+{
+    phys_offset = (unsigned long)start - XEN_VIRT_START;
+}
diff --git a/xen/arch/riscv/riscv64/head.S b/xen/arch/riscv/riscv64/head.S
index 6fb7dd80fd..69f3a24987 100644
--- a/xen/arch/riscv/riscv64/head.S
+++ b/xen/arch/riscv/riscv64/head.S
@@ -29,6 +29,8 @@ ENTRY(start)
 
         jal     reset_stack
 
+        jal     calc_phys_offset
+
         tail    start_xen
 
 ENTRY(reset_stack)
-- 
2.40.1