[Xen-changelog] [xen master] x86/boot: call reloc() using stdcall calling convention

[patchbot@xxxxxxx]

commit 8290b39f2b324c1c486ec42f952a1276c9904109
Author:     Daniel Kiper <daniel.kiper@xxxxxxxxxx>
AuthorDate: Thu Aug 25 14:02:53 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Aug 25 14:02:53 2016 +0200

    x86/boot: call reloc() using stdcall calling convention
    
    Current reloc() call method makes confusion and does not scale well
    for more arguments. And subsequent patch adding multiboot2 protocol
    support have to pass 3 arguments instead of 2. Hence, move reloc()
    call to stdcall calling convention. One may argue that we should use
    standard cdecl calling convention. However, stdcall is better here
    than cdecl because we do not need to remove "manually" arguments from
    stack in xen/arch/x86/boot/head.S assembly file.
    
    Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/boot/head.S  |  3 ++-
 xen/arch/x86/boot/reloc.c | 11 ++++++-----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 85770e8..5538a4b 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -119,7 +119,8 @@ __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
         mov     %eax,sym_phys(multiboot_ptr)
 
diff --git a/xen/arch/x86/boot/reloc.c b/xen/arch/x86/boot/reloc.c
index 9ae42e2..28c6cea 100644
--- a/xen/arch/x86/boot/reloc.c
+++ b/xen/arch/x86/boot/reloc.c
@@ -10,15 +10,16 @@
  *    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 %eax                     \n"
-    "    push 0x8(%esp)                \n"
-    "    call reloc                    \n"
-    "    ret  $0x4                     \n"
+    "    jmp  reloc                    \n"
     );
 
 typedef unsigned int u32;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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