[Xen-devel] [PATCH v3 03/16] x86/boot: call reloc() using cdecl calling convention

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

reloc() is not called according to cdecl calling convention.
This makes confusion and does not scale well for more arguments.
And patch adding multiboot2 protocol support have to pass 3
arguments instead of 2. Hence, move reloc() call to cdecl
calling convention.

I add push %ebp/mov %esp,%ebp/leave instructions here. Though they
are not strictly needed in this patch. However, then assembly code
in patch adding multiboot2 protocol support is easier to read.

Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
v3 - suggestions/fixes:
   - simplify assembly in xen/arch/x86/boot/reloc.c file
     (suggested by Jan Beulich),
   - reorder arguments for reloc() call from xen/arch/x86/boot/head.S
     (suggested by Jan Beulich),
   - improve commit message
     (suggested by Jan Beulich).
---
 xen/arch/x86/boot/head.S  |    4 +++-
 xen/arch/x86/boot/reloc.c |   18 ++++++++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 32a54a0..28ac721 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -119,8 +119,10 @@ __start:
 
         /* Save the Multiboot info struct (after relocation) for later use. */
         mov     $sym_phys(cpu0_stack)+1024,%esp
-        push    %ebx
+        push    %eax                /* Boot trampoline address. */
+        push    %ebx                /* Multiboot information address. */
         call    reloc
+        add     $8,%esp             /* Remove reloc() args from stack. */
         mov     %eax,sym_phys(multiboot_ptr)
 
         /* Initialize BSS (no nasty surprises!). */
diff --git a/xen/arch/x86/boot/reloc.c b/xen/arch/x86/boot/reloc.c
index 63045c0..006f41d 100644
--- a/xen/arch/x86/boot/reloc.c
+++ b/xen/arch/x86/boot/reloc.c
@@ -10,15 +10,25 @@
  *    Keir Fraser <keir@xxxxxxx>
  */
 
-/* entered with %eax = BOOT_TRAMPOLINE */
+/*
+ * This entry point is entered from xen/arch/x86/boot/head.S with:
+ *   - 0x4(%esp) = MULTIBOOT_INFORMATION_ADDRESS,
+ *   - 0x8(%esp) = BOOT_TRAMPOLINE_ADDRESS.
+ */
 asm (
     "    .text                         \n"
     "    .globl _start                 \n"
     "_start:                           \n"
+    "    push %ebp                     \n"
+    "    mov  %esp,%ebp                \n"
     "    call 1f                       \n"
-    "1:  pop  %ebx                     \n"
-    "    mov  %eax,alloc-1b(%ebx)      \n"
-    "    jmp  reloc                    \n"
+    "1:  pop  %ecx                     \n"
+    "    mov  0xc(%ebp),%eax           \n"
+    "    mov  %eax,alloc-1b(%ecx)      \n"
+    "    push 0x8(%ebp)                \n"
+    "    call reloc                    \n"
+    "    leave                         \n"
+    "    ret                           \n"
     );
 
 /*
-- 
1.7.10.4


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