[Xen-changelog] [xen staging] xen/arm32: head: Rework and document launch()

[patchbot@xxxxxxx]

commit 54c4ae18d158185891a646166388dc3ce7e8dc69
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Jul 22 16:08:30 2019 +0100
Commit:     Julien Grall <julien.grall@xxxxxxx>
CommitDate: Tue Sep 17 17:45:21 2019 +0100

    xen/arm32: head: Rework and document launch()
    
    Boot CPU and secondary CPUs will use different entry point to C code. At
    the moment, the decision on which entry to use is taken within launch().
    
    In order to avoid using conditional instruction and make the call
    clearer, launch() is reworked to take in parameters the entry point and its
    arguments.
    
    Lastly, document the behavior and the main registers usage within the
    function.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/arm32/head.S | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 8f945d318a..15d445eff7 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -163,6 +163,11 @@ primary_switched:
         /* Use a virtual address to access the UART. */
         mov_w r11, EARLY_UART_VIRTUAL_ADDRESS
 #endif
+        PRINT("- Ready -\r\n")
+        /* Setup the arguments for start_xen and jump to C world */
+        mov   r0, r10                /* r0 := Physical offset */
+        mov   r1, r8                 /* r1 := paddr(FDT) */
+        ldr   r2, =start_xen
         b     launch
 ENDPROC(start)
 
@@ -227,6 +232,9 @@ secondary_switched:
         /* Use a virtual address to access the UART. */
         mov_w r11, EARLY_UART_VIRTUAL_ADDRESS
 #endif
+        PRINT("- Ready -\r\n")
+        /* Jump to C world */
+        ldr   r2, =start_secondary
         b     launch
 ENDPROC(init_secondary)
 
@@ -517,19 +525,25 @@ setup_fixmap:
         mov   pc, lr
 ENDPROC(setup_fixmap)
 
+/*
+ * Setup the initial stack and jump to the C world
+ *
+ * Inputs:
+ *   r0 : Argument 0 of the C function to call
+ *   r1 : Argument 1 of the C function to call
+ *   r2 : C entry point
+ *
+ * Clobbers r3
+ */
 launch:
-        PRINT("- Ready -\r\n")
-
-        ldr   r0, =init_data
-        add   r0, #INITINFO_stack    /* Find the boot-time stack */
-        ldr   sp, [r0]
+        ldr   r3, =init_data
+        add   r3, #INITINFO_stack    /* Find the boot-time stack */
+        ldr   sp, [r3]
         add   sp, #STACK_SIZE        /* (which grows down from the top). */
         sub   sp, #CPUINFO_sizeof    /* Make room for CPU save record */
-        teq   r12, #0
-        moveq r0, r10                /* Marshal args: - phys_offset */
-        moveq r1, r8                 /*               - DTB address */
-        beq   start_xen              /* and disappear into the land of C */
-        b     start_secondary        /* (to the appropriate entry point) */
+
+        /* Jump to C world */
+       bx    r2
 ENDPROC(launch)
 
 /* Fail-stop */
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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