On 09.08.2019 17:01, David Woodhouse wrote:
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -735,7 +735,17 @@ trampoline_setup:
/* Switch to low-memory stack which lives at the end of trampoline
region. */
mov sym_fs(trampoline_phys),%edi
lea TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
+ cmpb $0, sym_fs(skip_realmode)
+ jz 1f
+ /* If no-real-mode, jump straight to trampoline_protmode_entry */
+ lea trampoline_protmode_entry-trampoline_start(%edi),%eax
+ /* EBX == 0 indicates we are the BP (Boot Processor). */
+ xor %ebx,%ebx
+ jmp 2f
+1:
+ /* Go via 16-bit code in trampoline_boot_cpu_entry */
lea trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
+2:
pushl $BOOT_CS32
push %eax
May I suggest to slightly streamline this into
/* Switch to low-memory stack which lives at the end of trampoline
region. */
mov sym_fs(trampoline_phys),%edi
lea TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
/* Go via 16-bit code in trampoline_boot_cpu_entry */
lea trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
cmpb $0,sym_fs(skip_realmode)
je 1f
/* If no-real-mode, jump straight to trampoline_protmode_entry */
lea trampoline_protmode_entry-trampoline_start(%edi),%eax
/* EBX == 0 indicates we are the BP (Boot Processor). */
xor %ebx,%ebx
1:
pushl $BOOT_CS32
push %eax
perhaps with the second slightly adapted to it now being an override
rather than an alternative path?
Additionally I think it would be nice if the clearing of %ebx wasn't
replicated here and ...
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -194,9 +194,6 @@ gdt_48: .word 6*8-1
.code32
trampoline_boot_cpu_entry:
- cmpb $0,bootsym_rel(skip_realmode,5)
- jnz .Lskip_realmode
-
/* Load pseudo-real-mode segments. */
mov $BOOT_PSEUDORM_DS,%eax
mov %eax,%ds
@@ -276,7 +273,6 @@ trampoline_boot_cpu_entry:
mov %eax,%gs
mov %eax,%ss
-.Lskip_realmode:
/* EBX == 0 indicates we are the BP (Boot Processor). */
xor %ebx,%ebx
... here. Why don't you further do
.code32
trampoline_protmode_entry_bsp:
/* EBX == 0 indicates we are the BSP (Boot Strap Processor). */
xor %ebx,%ebx
trampoline_protmode_entry:
directing the BSP paths to the new label?
Jan
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