diff mbox

[U-Boot,62/69] x86: Support a chained-boot development flow

Message ID 1457317732-18406-63-git-send-email-sjg@chromium.org
State Superseded
Delegated to: Bin Meng
Headers show

Commit Message

Simon Glass March 7, 2016, 2:28 a.m. UTC 
Sometimes it is useful to jump into U-Boot directly from coreboot or UEFI
without any 16-bit init. This can help during development by allowing U-Boot
to avoid doing all the init required by the platform.

In this case we cannot rely on the GDT settings. U-Boot will hang or crash
if these are wrong. Provide a development-only option to set up the GDT
correctly.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

 arch/x86/cpu/start.S | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

Comments

Bin Meng March 11, 2016, 8:46 a.m. UTC | #1 
Hi Simon,

On Mon, Mar 7, 2016 at 10:28 AM, Simon Glass <sjg@chromium.org> wrote:
> Sometimes it is useful to jump into U-Boot directly from coreboot or UEFI
> without any 16-bit init. This can help during development by allowing U-Boot
> to avoid doing all the init required by the platform.

I don't understand, why is coreboot having a problem here?

>
> In this case we cannot rely on the GDT settings. U-Boot will hang or crash
> if these are wrong. Provide a development-only option to set up the GDT
> correctly.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>
>  arch/x86/cpu/start.S | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
>
> diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
> index 485868f..5fbc2b5 100644
> --- a/arch/x86/cpu/start.S
> +++ b/arch/x86/cpu/start.S
> @@ -18,6 +18,13 @@
>  #include <generated/generic-asm-offsets.h>
>  #include <generated/asm-offsets.h>
>
> +/*
> + * Define this to boot U-Boot from a 32-bit program which sets the GDT
> + * differently. This can be used to boot directly from coreboot, for example.
> + * This is only useful for development.
> + */
> +#undef LOAD_FROM_32_BIT
> +
>  .section .text
>  .code32
>  .globl _start
> @@ -68,6 +75,10 @@ _start:
>         /* Save table pointer */
>         movl    %ecx, %esi
>
> +#ifdef LOAD_FROM_32_BIT
> +       lgdt    gdt_ptr2
> +#endif
> +
>         /* Load the segement registers to match the GDT loaded in start16.S */
>         movl    $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax
>         movw    %ax, %fs
> @@ -220,3 +231,71 @@ multiboot_header:
>         .long   0
>         /* entry addr */
>         .long   CONFIG_SYS_TEXT_BASE
> +
> +#ifdef LOAD_FROM_32_BIT
> +       /*
> +        * The following Global Descriptor Table is just enough to get us into
> +        * 'Flat Protected Mode' - It will be discarded as soon as the final
> +        * GDT is setup in a safe location in RAM
> +        */
> +gdt_ptr2:
> +       .word   0x1f            /* limit (31 bytes = 4 GDT entries - 1) */
> +       .long   gdt_rom2        /* base */
> +
> +       /* Some CPUs are picky about GDT alignment... */
> +       .align  16
> +.globl gdt_rom2
> +gdt_rom2:
> +       /*
> +        * The GDT table ...
> +        *
> +        *       Selector       Type
> +        *       0x00           NULL
> +        *       0x08           Unused
> +        *       0x10           32bit code
> +        *       0x18           32bit data/stack
> +        */
> +       /* The NULL Desciptor - Mandatory */
> +       .word   0x0000          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x00            /* access */
> +       .byte   0x00            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
> +
> +       /* Unused Desciptor - (matches Linux) */
> +       .word   0x0000          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x00            /* access */
> +       .byte   0x00            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
> +
> +       /*
> +        * The Code Segment Descriptor:
> +        * - Base   = 0x00000000
> +        * - Size   = 4GB
> +        * - Access = Present, Ring 0, Exec (Code), Readable
> +        * - Flags  = 4kB Granularity, 32-bit
> +        */
> +       .word   0xffff          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x9b            /* access */
> +       .byte   0xcf            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
> +
> +       /*
> +        * The Data Segment Descriptor:
> +        * - Base   = 0x00000000
> +        * - Size   = 4GB
> +        * - Access = Present, Ring 0, Non-Exec (Data), Writable
> +        * - Flags  = 4kB Granularity, 32-bit
> +        */
> +       .word   0xffff          /* limit_low */
> +       .word   0x0000          /* base_low */
> +       .byte   0x00            /* base_middle */
> +       .byte   0x93            /* access */
> +       .byte   0xcf            /* flags + limit_high */
> +       .byte   0x00            /* base_high */
> +#endif
> --

Regards,
Bin
Simon Glass March 12, 2016, 5:04 a.m. UTC | #2 
Hi Bin,

On 11 March 2016 at 01:46, Bin Meng <bmeng.cn@gmail.com> wrote:
> Hi Simon,
>
> On Mon, Mar 7, 2016 at 10:28 AM, Simon Glass <sjg@chromium.org> wrote:
>> Sometimes it is useful to jump into U-Boot directly from coreboot or UEFI
>> without any 16-bit init. This can help during development by allowing U-Boot
>> to avoid doing all the init required by the platform.
>
> I don't understand, why is coreboot having a problem here?

It's not coreboot, it's that U-Boot expects its GDT to be set up
correctly by its 16-bit code. If coreboot doesn't do this (because it
hasn't run the payload setup code yet) then this won't happen. This is
just a hack so you can jump to U-Boot from any stage of coreboot, not
just at the end.

>
>>
>> In this case we cannot rely on the GDT settings. U-Boot will hang or crash
>> if these are wrong. Provide a development-only option to set up the GDT
>> correctly.
>>
>> Signed-off-by: Simon Glass <sjg@chromium.org>
>> ---
>>
>>  arch/x86/cpu/start.S | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 79 insertions(+)
>>
>> diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
>> index 485868f..5fbc2b5 100644
>> --- a/arch/x86/cpu/start.S
>> +++ b/arch/x86/cpu/start.S
>> @@ -18,6 +18,13 @@
>>  #include <generated/generic-asm-offsets.h>
>>  #include <generated/asm-offsets.h>
>>
>> +/*
>> + * Define this to boot U-Boot from a 32-bit program which sets the GDT
>> + * differently. This can be used to boot directly from coreboot, for example.
>> + * This is only useful for development.
>> + */
>> +#undef LOAD_FROM_32_BIT
>> +
>>  .section .text
>>  .code32
>>  .globl _start
>> @@ -68,6 +75,10 @@ _start:
>>         /* Save table pointer */
>>         movl    %ecx, %esi
>>
>> +#ifdef LOAD_FROM_32_BIT
>> +       lgdt    gdt_ptr2
>> +#endif
>> +
>>         /* Load the segement registers to match the GDT loaded in start16.S */
>>         movl    $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax
>>         movw    %ax, %fs
>> @@ -220,3 +231,71 @@ multiboot_header:
>>         .long   0
>>         /* entry addr */
>>         .long   CONFIG_SYS_TEXT_BASE
>> +
>> +#ifdef LOAD_FROM_32_BIT
>> +       /*
>> +        * The following Global Descriptor Table is just enough to get us into
>> +        * 'Flat Protected Mode' - It will be discarded as soon as the final
>> +        * GDT is setup in a safe location in RAM
>> +        */
>> +gdt_ptr2:
>> +       .word   0x1f            /* limit (31 bytes = 4 GDT entries - 1) */
>> +       .long   gdt_rom2        /* base */
>> +
>> +       /* Some CPUs are picky about GDT alignment... */
>> +       .align  16
>> +.globl gdt_rom2
>> +gdt_rom2:
>> +       /*
>> +        * The GDT table ...
>> +        *
>> +        *       Selector       Type
>> +        *       0x00           NULL
>> +        *       0x08           Unused
>> +        *       0x10           32bit code
>> +        *       0x18           32bit data/stack
>> +        */
>> +       /* The NULL Desciptor - Mandatory */
>> +       .word   0x0000          /* limit_low */
>> +       .word   0x0000          /* base_low */
>> +       .byte   0x00            /* base_middle */
>> +       .byte   0x00            /* access */
>> +       .byte   0x00            /* flags + limit_high */
>> +       .byte   0x00            /* base_high */
>> +
>> +       /* Unused Desciptor - (matches Linux) */
>> +       .word   0x0000          /* limit_low */
>> +       .word   0x0000          /* base_low */
>> +       .byte   0x00            /* base_middle */
>> +       .byte   0x00            /* access */
>> +       .byte   0x00            /* flags + limit_high */
>> +       .byte   0x00            /* base_high */
>> +
>> +       /*
>> +        * The Code Segment Descriptor:
>> +        * - Base   = 0x00000000
>> +        * - Size   = 4GB
>> +        * - Access = Present, Ring 0, Exec (Code), Readable
>> +        * - Flags  = 4kB Granularity, 32-bit
>> +        */
>> +       .word   0xffff          /* limit_low */
>> +       .word   0x0000          /* base_low */
>> +       .byte   0x00            /* base_middle */
>> +       .byte   0x9b            /* access */
>> +       .byte   0xcf            /* flags + limit_high */
>> +       .byte   0x00            /* base_high */
>> +
>> +       /*
>> +        * The Data Segment Descriptor:
>> +        * - Base   = 0x00000000
>> +        * - Size   = 4GB
>> +        * - Access = Present, Ring 0, Non-Exec (Data), Writable
>> +        * - Flags  = 4kB Granularity, 32-bit
>> +        */
>> +       .word   0xffff          /* limit_low */
>> +       .word   0x0000          /* base_low */
>> +       .byte   0x00            /* base_middle */
>> +       .byte   0x93            /* access */
>> +       .byte   0xcf            /* flags + limit_high */
>> +       .byte   0x00            /* base_high */
>> +#endif
>> --
>
> Regards,
> Bin

Regards,
Simon
Bin Meng March 14, 2016, 6:38 a.m. UTC | #3 
Hi Simon,

On Sat, Mar 12, 2016 at 1:04 PM, Simon Glass <sjg@chromium.org> wrote:
> Hi Bin,
>
> On 11 March 2016 at 01:46, Bin Meng <bmeng.cn@gmail.com> wrote:
>> Hi Simon,
>>
>> On Mon, Mar 7, 2016 at 10:28 AM, Simon Glass <sjg@chromium.org> wrote:
>>> Sometimes it is useful to jump into U-Boot directly from coreboot or UEFI
>>> without any 16-bit init. This can help during development by allowing U-Boot
>>> to avoid doing all the init required by the platform.
>>
>> I don't understand, why is coreboot having a problem here?
>
> It's not coreboot, it's that U-Boot expects its GDT to be set up
> correctly by its 16-bit code. If coreboot doesn't do this (because it
> hasn't run the payload setup code yet) then this won't happen. This is
> just a hack so you can jump to U-Boot from any stage of coreboot, not
> just at the end.

OK, please add some clarification in the commit message and/or the
code comments below.

>
>>
>>>
>>> In this case we cannot rely on the GDT settings. U-Boot will hang or crash
>>> if these are wrong. Provide a development-only option to set up the GDT
>>> correctly.
>>>
>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>> ---
>>>
>>>  arch/x86/cpu/start.S | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 79 insertions(+)
>>>
>>> diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
>>> index 485868f..5fbc2b5 100644
>>> --- a/arch/x86/cpu/start.S
>>> +++ b/arch/x86/cpu/start.S
>>> @@ -18,6 +18,13 @@
>>>  #include <generated/generic-asm-offsets.h>
>>>  #include <generated/asm-offsets.h>
>>>
>>> +/*
>>> + * Define this to boot U-Boot from a 32-bit program which sets the GDT
>>> + * differently. This can be used to boot directly from coreboot, for example.

Needs some clarifications on "boot directly from coreboot"

>>> + * This is only useful for development.
>>> + */
>>> +#undef LOAD_FROM_32_BIT
>>> +
>>>  .section .text
>>>  .code32
>>>  .globl _start
>>> @@ -68,6 +75,10 @@ _start:
>>>         /* Save table pointer */
>>>         movl    %ecx, %esi
>>>
>>> +#ifdef LOAD_FROM_32_BIT
>>> +       lgdt    gdt_ptr2
>>> +#endif
>>> +
>>>         /* Load the segement registers to match the GDT loaded in start16.S */
>>>         movl    $(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax
>>>         movw    %ax, %fs
>>> @@ -220,3 +231,71 @@ multiboot_header:
>>>         .long   0
>>>         /* entry addr */
>>>         .long   CONFIG_SYS_TEXT_BASE
>>> +
>>> +#ifdef LOAD_FROM_32_BIT
>>> +       /*
>>> +        * The following Global Descriptor Table is just enough to get us into
>>> +        * 'Flat Protected Mode' - It will be discarded as soon as the final
>>> +        * GDT is setup in a safe location in RAM
>>> +        */
>>> +gdt_ptr2:
>>> +       .word   0x1f            /* limit (31 bytes = 4 GDT entries - 1) */
>>> +       .long   gdt_rom2        /* base */
>>> +
>>> +       /* Some CPUs are picky about GDT alignment... */
>>> +       .align  16
>>> +.globl gdt_rom2
>>> +gdt_rom2:
>>> +       /*
>>> +        * The GDT table ...
>>> +        *
>>> +        *       Selector       Type
>>> +        *       0x00           NULL
>>> +        *       0x08           Unused
>>> +        *       0x10           32bit code
>>> +        *       0x18           32bit data/stack
>>> +        */
>>> +       /* The NULL Desciptor - Mandatory */
>>> +       .word   0x0000          /* limit_low */
>>> +       .word   0x0000          /* base_low */
>>> +       .byte   0x00            /* base_middle */
>>> +       .byte   0x00            /* access */
>>> +       .byte   0x00            /* flags + limit_high */
>>> +       .byte   0x00            /* base_high */
>>> +
>>> +       /* Unused Desciptor - (matches Linux) */
>>> +       .word   0x0000          /* limit_low */
>>> +       .word   0x0000          /* base_low */
>>> +       .byte   0x00            /* base_middle */
>>> +       .byte   0x00            /* access */
>>> +       .byte   0x00            /* flags + limit_high */
>>> +       .byte   0x00            /* base_high */
>>> +
>>> +       /*
>>> +        * The Code Segment Descriptor:
>>> +        * - Base   = 0x00000000
>>> +        * - Size   = 4GB
>>> +        * - Access = Present, Ring 0, Exec (Code), Readable
>>> +        * - Flags  = 4kB Granularity, 32-bit
>>> +        */
>>> +       .word   0xffff          /* limit_low */
>>> +       .word   0x0000          /* base_low */
>>> +       .byte   0x00            /* base_middle */
>>> +       .byte   0x9b            /* access */
>>> +       .byte   0xcf            /* flags + limit_high */
>>> +       .byte   0x00            /* base_high */
>>> +
>>> +       /*
>>> +        * The Data Segment Descriptor:
>>> +        * - Base   = 0x00000000
>>> +        * - Size   = 4GB
>>> +        * - Access = Present, Ring 0, Non-Exec (Data), Writable
>>> +        * - Flags  = 4kB Granularity, 32-bit
>>> +        */
>>> +       .word   0xffff          /* limit_low */
>>> +       .word   0x0000          /* base_low */
>>> +       .byte   0x00            /* base_middle */
>>> +       .byte   0x93            /* access */
>>> +       .byte   0xcf            /* flags + limit_high */
>>> +       .byte   0x00            /* base_high */
>>> +#endif
>>> --

Regards,
Bin
diff mbox

Patch

diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S
index 485868f..5fbc2b5 100644
--- a/arch/x86/cpu/start.S
+++ b/arch/x86/cpu/start.S
@@ -18,6 +18,13 @@ 
 #include <generated/generic-asm-offsets.h>
 #include <generated/asm-offsets.h>
 
+/*
+ * Define this to boot U-Boot from a 32-bit program which sets the GDT
+ * differently. This can be used to boot directly from coreboot, for example.
+ * This is only useful for development.
+ */
+#undef LOAD_FROM_32_BIT
+
 .section .text
 .code32
 .globl _start
@@ -68,6 +75,10 @@  _start:
 	/* Save table pointer */
 	movl	%ecx, %esi
 
+#ifdef LOAD_FROM_32_BIT
+	lgdt	gdt_ptr2
+#endif
+
 	/* Load the segement registers to match the GDT loaded in start16.S */
 	movl	$(X86_GDT_ENTRY_32BIT_DS * X86_GDT_ENTRY_SIZE), %eax
 	movw	%ax, %fs
@@ -220,3 +231,71 @@  multiboot_header:
 	.long	0
 	/* entry addr */
 	.long	CONFIG_SYS_TEXT_BASE
+
+#ifdef LOAD_FROM_32_BIT
+	/*
+	 * The following Global Descriptor Table is just enough to get us into
+	 * 'Flat Protected Mode' - It will be discarded as soon as the final
+	 * GDT is setup in a safe location in RAM
+	 */
+gdt_ptr2:
+	.word	0x1f		/* limit (31 bytes = 4 GDT entries - 1) */
+	.long	gdt_rom2	/* base */
+
+	/* Some CPUs are picky about GDT alignment... */
+	.align	16
+.globl gdt_rom2
+gdt_rom2:
+	/*
+	 * The GDT table ...
+	 *
+	 *	 Selector	Type
+	 *	 0x00		NULL
+	 *	 0x08		Unused
+	 *	 0x10		32bit code
+	 *	 0x18		32bit data/stack
+	 */
+	/* The NULL Desciptor - Mandatory */
+	.word	0x0000		/* limit_low */
+	.word	0x0000		/* base_low */
+	.byte	0x00		/* base_middle */
+	.byte	0x00		/* access */
+	.byte	0x00		/* flags + limit_high */
+	.byte	0x00		/* base_high */
+
+	/* Unused Desciptor - (matches Linux) */
+	.word	0x0000		/* limit_low */
+	.word	0x0000		/* base_low */
+	.byte	0x00		/* base_middle */
+	.byte	0x00		/* access */
+	.byte	0x00		/* flags + limit_high */
+	.byte	0x00		/* base_high */
+
+	/*
+	 * The Code Segment Descriptor:
+	 * - Base   = 0x00000000
+	 * - Size   = 4GB
+	 * - Access = Present, Ring 0, Exec (Code), Readable
+	 * - Flags  = 4kB Granularity, 32-bit
+	 */
+	.word	0xffff		/* limit_low */
+	.word	0x0000		/* base_low */
+	.byte	0x00		/* base_middle */
+	.byte	0x9b		/* access */
+	.byte	0xcf		/* flags + limit_high */
+	.byte	0x00		/* base_high */
+
+	/*
+	 * The Data Segment Descriptor:
+	 * - Base   = 0x00000000
+	 * - Size   = 4GB
+	 * - Access = Present, Ring 0, Non-Exec (Data), Writable
+	 * - Flags  = 4kB Granularity, 32-bit
+	 */
+	.word	0xffff		/* limit_low */
+	.word	0x0000		/* base_low */
+	.byte	0x00		/* base_middle */
+	.byte	0x93		/* access */
+	.byte	0xcf		/* flags + limit_high */
+	.byte	0x00		/* base_high */
+#endif