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author | Michael Brown | 2016-02-19 02:50:13 +0100 |
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committer | Michael Brown | 2016-02-19 03:58:09 +0100 |
commit | d1562c38a6882a129998935cd63d09ab18f77add (patch) | |
tree | e834487ca48085ca2f62d200419e6a839301a514 /src/arch/x86/transitions/librm.S | |
parent | [relocate] Preserve page alignment during relocation (diff) | |
download | ipxe-d1562c38a6882a129998935cd63d09ab18f77add.tar.gz ipxe-d1562c38a6882a129998935cd63d09ab18f77add.tar.xz ipxe-d1562c38a6882a129998935cd63d09ab18f77add.zip |
[librm] Prepare for long-mode memory map
The bulk of the iPXE binary (the .textdata section) is physically
relocated at runtime to the top of the 32-bit address space in order
to allow space for an OS to be loaded. The relocation is achieved
with the assistance of segmentation: we adjust the code and data
segment bases so that the link-time addresses remain valid.
Segmentation is not available (for normal code and data segments) in
long mode. We choose to compile the C code with -mcmodel=kernel and
use a link-time address of 0xffffffffeb000000. This choice allows us
to identity-map the entirety of the 32-bit address space, and to alias
our chosen link-time address to the physical location of our .textdata
section. (This requires the .textdata section to always be aligned to
a page boundary.)
We simultaneously choose to set the 32-bit virtual address segment
bases such that the link-time addresses may simply be truncated to 32
bits in order to generate a valid 32-bit virtual address. This allows
symbols in .textdata to be trivially accessed by both 32-bit and
64-bit code.
There is no (sensible) way in 32-bit assembly code to generate the
required R_X86_64_32S relocation records for these truncated symbols.
However, subtracting the fixed constant 0xffffffff00000000 has the
same effect as truncation, and can be represented in a standard
R_X86_64_32 relocation record. We define the VIRTUAL() macro to
abstract away this truncation operation, and apply it to all
references by 32-bit (or 16-bit) assembly code to any symbols within
the .textdata section.
We define "virt_offset" for a 64-bit build as "the value to be added
to an address within .textdata in order to obtain its physical
address". With this definition, the low 32 bits of "virt_offset" can
be treated by 32-bit code as functionally equivalent to "virt_offset"
in a 32-bit build.
We define "text16" and "data16" for a 64-bit build as the physical
addresses of the .text16 and .data16 sections. Since a physical
address within the 32-bit address space may be used directly as a
64-bit virtual address (thanks to the identity map), this definition
provides the most natural access to variables in .text16 and .data16.
Note that this requires a minor adjustment in prot_to_real(), which
accesses .text16 using 32-bit virtual addresses.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Diffstat (limited to 'src/arch/x86/transitions/librm.S')
-rw-r--r-- | src/arch/x86/transitions/librm.S | 65 |
1 files changed, 42 insertions, 23 deletions
diff --git a/src/arch/x86/transitions/librm.S b/src/arch/x86/transitions/librm.S index 42cfb991..495f272d 100644 --- a/src/arch/x86/transitions/librm.S +++ b/src/arch/x86/transitions/librm.S @@ -19,8 +19,22 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ) #define SIZEOF_REAL_MODE_REGS ( SIZEOF_I386_SEG_REGS + SIZEOF_I386_REGS ) #define SIZEOF_I386_FLAGS 4 #define SIZEOF_I386_ALL_REGS ( SIZEOF_REAL_MODE_REGS + SIZEOF_I386_FLAGS ) - - .arch i386 + +/* Size of an address */ +#ifdef __x86_64__ +#define SIZEOF_ADDR 8 +#else +#define SIZEOF_ADDR 4 +#endif + +/* Selectively assemble code for 32-bit/64-bit builds */ +#ifdef __x86_64__ +#define if32 if 0 +#define if64 if 1 +#else +#define if32 if 1 +#define if64 if 0 +#endif /**************************************************************************** * Global descriptor table @@ -126,7 +140,7 @@ rm_sp: .word 0 rm_ss: .word 0 .section ".data.pm_esp", "aw", @progbits -pm_esp: .long _estack +pm_esp: .long VIRTUAL(_estack) /**************************************************************************** * Virtual address offsets @@ -137,9 +151,9 @@ pm_esp: .long _estack **************************************************************************** */ .struct 0 -VA_VIRT_OFFSET: .space 4 -VA_TEXT16: .space 4 -VA_DATA16: .space 4 +VA_VIRT_OFFSET: .space SIZEOF_ADDR +VA_TEXT16: .space SIZEOF_ADDR +VA_DATA16: .space SIZEOF_ADDR VA_SIZE: .previous @@ -168,7 +182,7 @@ virt_addrs: .space VA_SIZE * Parameters: * %cs : .text16 segment * %ds : .data16 segment - * %edi : Physical base of protected-mode code (virt_offset) + * %edi : Physical base of protected-mode code **************************************************************************** */ .section ".text16.init_librm", "ax", @progbits @@ -181,7 +195,9 @@ init_librm: pushl %edi /* Store rm_virt_offset and set up virtual_cs and virtual_ds segments */ + subl $VIRTUAL(_textdata), %edi movl %edi, rm_virt_offset +.if64 ; setae (rm_virt_offset+4) ; .endif movl %edi, %eax movw $virtual_cs, %bx call set_seg_base @@ -195,7 +211,7 @@ init_librm: shll $4, %eax movw $real_cs, %bx call set_seg_base - subl %edi, %eax +.if32 ; subl %edi, %eax ; .endif movl %eax, rm_text16 /* Store rm_ds and rm_data16, set up real_ds segment and GDT base */ @@ -207,7 +223,7 @@ init_librm: call set_seg_base movl %eax, gdt_base addl $gdt, gdt_base - subl %edi, %eax +.if32 ; subl %edi, %eax ; .endif movl %eax, rm_data16 /* Switch to protected mode */ @@ -221,7 +237,7 @@ init_librm_pmode: movw $REAL_DS, %ax movw %ax, %ds movl $rm_virt_addrs, %esi - movl $virt_addrs, %edi + movl $VIRTUAL(virt_addrs), %edi movl $( VA_SIZE / 4 ), %ecx rep movsl popw %ds @@ -312,7 +328,7 @@ real_to_prot: movl %cr0, %eax orb $CR0_PE, %al movl %eax, %cr0 - data32 ljmp $VIRTUAL_CS, $r2p_pmode + data32 ljmp $VIRTUAL_CS, $VIRTUAL(r2p_pmode) .section ".text.real_to_prot", "ax", @progbits .code32 r2p_pmode: @@ -323,15 +339,15 @@ r2p_pmode: movw %ax, %fs movw %ax, %gs movw %ax, %ss - movl pm_esp, %esp + movl VIRTUAL(pm_esp), %esp /* Load protected-mode interrupt descriptor table */ - lidt idtr + lidt VIRTUAL(idtr) /* Record real-mode %ss:sp (after removal of data) */ - movw %bp, rm_ss + movw %bp, VIRTUAL(rm_ss) addl %ecx, %edx - movw %dx, rm_sp + movw %dx, VIRTUAL(rm_sp) /* Move data from RM stack to PM stack */ subl %ecx, %esp @@ -365,7 +381,8 @@ r2p_pmode: .code32 prot_to_real: /* Copy real-mode global descriptor table register to RM code segment */ - movl text16, %edi + movl VIRTUAL(text16), %edi +.if64 ; subl VIRTUAL(virt_offset), %edi ; .endif leal rm_gdtr(%edi), %edi movsw movsl @@ -377,20 +394,20 @@ prot_to_real: addl $4, %ecx /* Real-mode %ss:sp => %ebp:edx and virtual address => %edi */ - movzwl rm_ss, %ebp - movzwl rm_sp, %edx + movzwl VIRTUAL(rm_ss), %ebp + movzwl VIRTUAL(rm_sp), %edx subl %ecx, %edx movl %ebp, %eax shll $4, %eax leal (%eax,%edx), %edi - subl virt_offset, %edi + subl VIRTUAL(virt_offset), %edi /* Move data from PM stack to RM stack */ movl %esp, %esi rep movsb /* Record protected-mode %esp (after removal of data) */ - movl %esi, pm_esp + movl %esi, VIRTUAL(pm_esp) /* Load real-mode segment limits */ movw $P2R_DS, %ax @@ -512,7 +529,7 @@ prot_call: /* Switch to protected mode and move register dump to PM stack */ movl $PC_OFFSET_END, %ecx - pushl $pc_pmode + pushl $VIRTUAL(pc_pmode) jmp real_to_prot .section ".text.prot_call", "ax", @progbits .code32 @@ -589,7 +606,7 @@ real_call: /* Switch to real mode and move register dump to RM stack */ movl $( RC_OFFSET_REGS_END + 4 /* function pointer copy */ ), %ecx pushl $rc_rmode - movl $rm_default_gdtr_idtr, %esi + movl $VIRTUAL(rm_default_gdtr_idtr), %esi jmp prot_to_real .section ".text16.real_call", "ax", @progbits .code16 @@ -605,7 +622,7 @@ rc_rmode: /* Switch to protected mode and move register dump back to PM stack */ movl $RC_OFFSET_REGS_END, %ecx - pushl $rc_pmode + pushl $VIRTUAL(rc_pmode) jmp real_to_prot .section ".text.real_call", "ax", @progbits .code32 @@ -665,6 +682,8 @@ flatten_dummy: * May be entered with either physical or virtual stack segment. **************************************************************************** */ + .section ".text.interrupt_wrapper", "ax", @progbits + .code32 .globl interrupt_wrapper interrupt_wrapper: /* Preserve segment registers and original %esp */ |