Re: [Minios-devel] [UNIKRAFT PATCH v2 01/18] plat/kvm: Place early boot code to the start of the image (x86)

[Yuri Volchkov <yuri.volchkov@xxxxxxxxx>]

Simon Kuenzer <simon.kuenzer@xxxxxxxxx> writes:

> Places early boot code (e.g., 64bit mode switch) and
> data (e.g., GDT) to the start of the image.
> This avoids general protection faults that were caused
> whenever the linker placed such items to addresses
> that were not accessible while the mode switch to 64bit
> and address space setup was not finished.
>
> Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> ---
>  plat/kvm/x86/entry64.S | 21 ++++++++++++---------
>  plat/kvm/x86/link64.ld |  3 ++-
>  2 files changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/plat/kvm/x86/entry64.S b/plat/kvm/x86/entry64.S
> index bda7d40..1a10359 100644
> --- a/plat/kvm/x86/entry64.S
> +++ b/plat/kvm/x86/entry64.S
> @@ -30,24 +30,24 @@
>  #include <x86/cpu_defs.h>
>  #include <kvm-x86/multiboot_defs.h>
>  
> -#define ENTRY(x) .text; .globl x; .type x,%function; x:
> +#define ENTRY(x) .globl x; .type x,%function; x:
>  #define END(x)   .size x, . - x
>  
>  #define MYMULTIBOOT_FLAGS \
>      (MULTIBOOT_PAGE_ALIGN | MULTIBOOT_MEMORY_INFO | MULTIBOOT_AOUT_KLUDGE)
>  
> -.section .data.multiboot
> +.section .data.boot
>  
>  .align 4
>  _multiboot_header:
>  .long MULTIBOOT_HEADER_MAGIC
>  .long MYMULTIBOOT_FLAGS
> -.long -(MULTIBOOT_HEADER_MAGIC+MYMULTIBOOT_FLAGS)
> -.long _multiboot_header
> -.long 0x100000
> -.long _edata
> -.long _end
> -.long _libkvmplat_start32
> +.long -(MULTIBOOT_HEADER_MAGIC+MYMULTIBOOT_FLAGS) /* checksum */
> +.long _multiboot_header                           /* header addr */
> +.long 0x100000                                    /* load addr */
> +.long _edata                                      /* load end addr */
> +.long _end                                        /* bss end addr */
> +.long _libkvmplat_start32                         /* entry addr */
>  
>  .section .bss
>  
> @@ -63,6 +63,7 @@ bootstack:
>   * we've switched to long mode.
>   */
>  .code32
> +.section .text.boot
>  
>  ENTRY(_libkvmplat_start32)
>       cld
> @@ -139,7 +140,7 @@ END(_libkvmplat_start32)
>   * Uuuyea, exceptions.
>   */
>  
> -.data
> +.section .data.boot
>  .align 64
>  gdt64:
>       .quad 0x0000000000000000
> @@ -165,6 +166,7 @@ mxcsr_ptr:
>  #include "pagetable.S"
>  
>  .code64
> +.section .text.boot
>  
>  ENTRY(_libkvmplat_start64)
>       movq $bootstack, %rsp
> @@ -192,6 +194,7 @@ ENTRY(_libkvmplat_start64)
>       hlt
>  END(_libkvmplat_start64)
>  
> +.text
>  ENTRY(_libkvmplat_newstack)
>       movq %rdi, %rsp
>       movq %rdx, %rdi
> diff --git a/plat/kvm/x86/link64.ld b/plat/kvm/x86/link64.ld
> index d1bfa73..60b5d21 100644
> --- a/plat/kvm/x86/link64.ld
> +++ b/plat/kvm/x86/link64.ld
> @@ -33,7 +33,8 @@ SECTIONS
>       .text :
>       {
>               /* prevent linker gc from removing multiboot header */
> -             KEEP (*(.data.multiboot))
> +             KEEP (*(.data.boot))
> +             *(.text.boot)
>  
>               *(.text)
>               *(.text.*)
> -- 
> 2.7.4
>

-- 
Yuri Volchkov
Software Specialist

NEC Europe Ltd
Kurfürsten-Anlage 36
D-69115 Heidelberg

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