xen/arm64: head: Allow to use early printk while on 1:1 mapping

Take an example from commit 1ec3fe1f66 ("xen/arm32: head: Improve
logging in head.S") to add support for printing early boot messages
while running on identity mapping:
 - define PRINT_SECT() macro to be able to specify a section for storing
   a string. PRINT() will use .rodata.str and PRINT_ID() - .rodata.idmap.
   This is necessary, because when running on identity mapping, the
   strings need to be part of the first page that is mapped,
 - move loading a runtime virtual UART address right after enabling MMU
   (the corresponding steps repeated in {primary,secondary}_switched are
   now consolidated in a single place),
 - move early printk 'hex' string into .rodata.idmap and replace 'adr'
   instruction in asm_putn with 'adr_l' to extend the addressable range,
 - remove RODATA_STR() macro given no use.

Signed-off-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/arm64/head.S

@@ -256,10 +256,6 @@ real_start_efi:
         b     enable_boot_cpu_mm
 
 primary_switched:
-#ifdef CONFIG_EARLY_PRINTK
-        /* Use a virtual address to access the UART. */
-        ldr   x23, =EARLY_UART_VIRTUAL_ADDRESS
-#endif
         bl    zero_bss
         PRINT("- Ready -\r\n")
         /* Setup the arguments for start_xen and jump to C world */
@@ -304,10 +300,6 @@ GLOBAL(init_secondary)
         b     enable_secondary_cpu_mm
 
 secondary_switched:
-#ifdef CONFIG_EARLY_PRINTK
-        /* Use a virtual address to access the UART. */
-        ldr   x23, =EARLY_UART_VIRTUAL_ADDRESS
-#endif
         PRINT("- Ready -\r\n")
         /* Jump to C world */
         ldr   x2, =start_secondary
@@ -480,7 +472,7 @@ ENDPROC(asm_puts)
  * Clobbers x0-x3
  */
 ENTRY(asm_putn)
-        adr   x1, hex
+        adr_l x1, hex
         mov   x3, #16
 1:
         early_uart_ready x23, 2
@@ -494,8 +486,7 @@ ENTRY(asm_putn)
         ret
 ENDPROC(asm_putn)
 
-hex:    .ascii "0123456789abcdef"
-        .align 2
+RODATA_SECT(.rodata.idmap, hex, "0123456789abcdef")
 
 #endif /* CONFIG_EARLY_PRINTK */
 

xen/arch/arm/arm64/mmu/head.S

@@ -295,6 +295,14 @@ enable_mmu:
         dsb   sy                     /* Flush PTE writes and finish reads */
         msr   SCTLR_EL2, x0          /* now paging is enabled */
         isb                          /* Now, flush the icache */
+
+#ifdef CONFIG_EARLY_PRINTK
+        /* Use a virtual address to access the UART. */
+        ldr   x23, =EARLY_UART_VIRTUAL_ADDRESS
+#endif
+
+        PRINT_ID("- Paging turned on -\r\n")
+
         ret
 ENDPROC(enable_mmu)
 

xen/arch/arm/include/asm/arm64/macros.h

@@ -34,16 +34,26 @@
 
 #ifdef CONFIG_EARLY_PRINTK
 /*
- * Macro to print a string to the UART, if there is one.
+ * Macros to print a string to the UART, if there is one.
+ *
+ * There are multiple flavors:
+ *  - PRINT_SECT(section, string): The @string will be located in @section
+ *  - PRINT(): The string will be located in .rodata.str.
+ *  - PRINT_ID(): When Xen is running on the Identity Mapping, it is
+ *    only possible to have a limited amount of Xen. This will create
+ *    the string in .rodata.idmap which will always be mapped.
  *
  * Clobbers x0 - x3
  */
-#define PRINT(_s)          \
-        mov   x3, lr ;     \
-        adr_l x0, 98f ;    \
-        bl    asm_puts ;   \
-        mov   lr, x3 ;     \
-        RODATA_STR(98, _s)
+#define PRINT_SECT(section, string)         \
+        mov   x3, lr                       ;\
+        adr_l x0, 98f                      ;\
+        bl    asm_puts                     ;\
+        mov   lr, x3                       ;\
+        RODATA_SECT(section, 98, string)
+
+#define PRINT(string) PRINT_SECT(.rodata.str, string)
+#define PRINT_ID(string) PRINT_SECT(.rodata.idmap, string)
 
 /*
  * Macro to print the value of register \xb
@@ -59,6 +69,7 @@
 
 #else /* CONFIG_EARLY_PRINTK */
 #define PRINT(s)
+#define PRINT_ID(s)
 
 .macro print_reg xb
 .endm

xen/arch/arm/include/asm/asm_defns.h

@@ -27,8 +27,6 @@
 label:  .asciz msg;                             \
 .popsection
 
-#define RODATA_STR(label, msg) RODATA_SECT(.rodata.str, label, msg)
-
 #define ASM_INT(label, val)                 \
     .p2align 2;                             \
 label: .long (val);                         \