Loading the VGA base address involves sym_esi(), i.e. %esi still needs
to hold the relocation base address. Therefore the address of the
message to output cannot be "passed" in %esi. Put the message offset in
%ecx instead, adding it into %esi _after_ its last use as base address.
Fixes: b28044226e1c ("x86: make Xen early boot code relocatable")
Signed-off-by: Jan Beulich <[email protected]>
---
This also suggests that 78e693cc1232 ("x86/boot: fix early error
output") was only tested for the no-VGA case (i.e. EFI+MB2), and only
for one of the two paths which bypass the loading of %edi at .Lget_vtb
(or the offset load merely was lucky to pick up a zero).
Clearly when using "vga=current" with MB2 when the screen is already in
graphics mode, there will continue to be no visible output.
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -146,17 +146,17 @@ efi_platform:
early_error: /* Here to improve the disassembly. */
.Lbad_cpu:
- add $sym_offs(.Lbad_cpu_msg), %esi
+ mov $sym_offs(.Lbad_cpu_msg), %ecx
jmp .Lget_vtb
.Lnot_multiboot:
- add $sym_offs(.Lbad_ldr_msg), %esi
+ mov $sym_offs(.Lbad_ldr_msg), %ecx
jmp .Lget_vtb
.Lnot_aligned:
- add $sym_offs(.Lbag_alg_msg), %esi
+ mov $sym_offs(.Lbag_alg_msg), %ecx
jmp .Lget_vtb
#ifdef CONFIG_REQUIRE_NX
.Lno_nx:
- add $sym_offs(.Lno_nx_msg), %esi
+ mov $sym_offs(.Lno_nx_msg), %ecx
jmp .Lget_vtb
#endif
.Lmb2_no_st:
@@ -164,11 +164,11 @@ early_error: /* Here to improve the disa
* Here we are on EFI platform. vga_text_buffer was zapped earlier
* because there is pretty good chance that VGA is unavailable.
*/
- add $sym_offs(.Lbad_ldr_nst), %esi
+ mov $sym_offs(.Lbad_ldr_nst), %ecx
jmp .Lget_vtb
.Lmb2_no_ih:
/* Ditto. */
- add $sym_offs(.Lbad_ldr_nih), %esi
+ mov $sym_offs(.Lbad_ldr_nih), %ecx
jmp .Lget_vtb
.Lmb2_no_bs:
/*
@@ -176,7 +176,7 @@ early_error: /* Here to improve the disa
* via start label. Then reliable vga_text_buffer zap is impossible
* in Multiboot2 scanning loop and we have to zero %edi below.
*/
- add $sym_offs(.Lbad_ldr_nbs), %esi
+ mov $sym_offs(.Lbad_ldr_nbs), %ecx
xor %edi,%edi # No VGA text buffer
jmp .Lprint_err
.Lmb2_efi_ia_32:
@@ -184,12 +184,15 @@ early_error: /* Here to improve the disa
* Here we are on EFI IA-32 platform. Then reliable vga_text_buffer
zap is
* impossible in Multiboot2 scanning loop and we have to zero %edi
below.
*/
- add $sym_offs(.Lbad_efi_msg), %esi
+ mov $sym_offs(.Lbad_efi_msg), %ecx
xor %edi,%edi # No VGA text buffer
jmp .Lprint_err
.Lget_vtb:
mov sym_esi(vga_text_buffer), %edi
.Lprint_err:
+ add %ecx, %esi # Add string offset to relocation base.
+ # NOTE: No further use of sym_esi() till the end of the "function"!
+1:
lodsb
test %al,%al # Terminate on '\0' sentinel
je .Lhalt
@@ -202,11 +205,11 @@ early_error: /* Here to improve the disa
mov %bl,%al
out %al,%dx # Send a character over the serial line
test %edi,%edi # Is the VGA text buffer available?
- jz .Lprint_err
+ jz 1b
stosb # Write a character to the VGA text buffer
mov $7,%al
stosb # Write an attribute to the VGA text buffer
- jmp .Lprint_err
+ jmp 1b
.Lhalt: hlt
jmp .Lhalt
