[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>
This commit is contained in:
Michael Brown
parent
bfe6e3e90e
commit
d1562c38a6
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@ -32,13 +32,13 @@ _virt_to_phys:
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pushl %ebp
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/* Change return address to a physical address */
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movl virt_offset, %ebp
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movl VIRTUAL(virt_offset), %ebp
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addl %ebp, 12(%esp)
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/* Switch to physical code segment */
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cli
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pushl $PHYSICAL_CS
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leal 1f(%ebp), %eax
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leal VIRTUAL(1f)(%ebp), %eax
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pushl %eax
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lret
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1:
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@ -78,7 +78,7 @@ _phys_to_virt:
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/* Switch to virtual code segment */
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cli
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ljmp $VIRTUAL_CS, $1f
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ljmp $VIRTUAL_CS, $VIRTUAL(1f)
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1:
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/* Reload data segment registers */
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movl $VIRTUAL_DS, %eax
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@ -88,7 +88,7 @@ _phys_to_virt:
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movl %eax, %gs
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/* Reload stack segment and adjust %esp */
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movl virt_offset, %ebp
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movl VIRTUAL(virt_offset), %ebp
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movl %eax, %ss
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subl %ebp, %esp
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@ -134,7 +134,7 @@ _intr_to_virt:
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/* Reload stack segment and adjust %esp if necessary */
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je 1f
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movl virt_offset, %ebp
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movl VIRTUAL(virt_offset), %ebp
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movl %eax, %ss
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subl %ebp, %esp
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1:
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@ -7,7 +7,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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*
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* Don't change these unless you really know what you're doing.
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*/
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#define VIRTUAL_CS 0x08
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#define VIRTUAL_DS 0x10
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#define PHYSICAL_CS 0x18
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@ -16,6 +15,40 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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#define REAL_DS 0x30
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#define P2R_DS 0x38
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/* Calculate symbol address within VIRTUAL_CS or VIRTUAL_DS
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*
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* In a 64-bit build, we set the bases of VIRTUAL_CS and VIRTUAL_DS
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* such that truncating a .textdata symbol value to 32 bits gives a
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* valid 32-bit virtual address.
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*
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* The C code is compiled with -mcmodel=kernel and so we must place
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* all .textdata symbols within the negative 2GB of the 64-bit address
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* space. Consequently, all .textdata symbols will have the MSB set
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* after truncation to 32 bits. This means that a straightforward
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* R_X86_64_32 relocation record for the symbol will fail, since the
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* truncated symbol value will not correctly zero-extend to the
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* original 64-bit value.
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*
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* Using an R_X86_64_32S relocation record would work, but there is no
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* (sensible) way to generate these relocation records within 32-bit
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* or 16-bit code.
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*
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* The simplest solution is to generate an R_X86_64_32 relocation
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* record with an addend of (-0xffffffff00000000). Since all
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* .textdata symbols are within the negative 2GB of the 64-bit address
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* space, this addend acts to effectively truncate the symbol to 32
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* bits, thereby matching the semantics of the R_X86_64_32 relocation
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* records generated for 32-bit and 16-bit code.
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*
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* In a 32-bit build, this problem does not exist, and we can just use
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* the .textdata symbol values directly.
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*/
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#ifdef __x86_64__
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#define VIRTUAL(address) ( (address) - 0xffffffff00000000 )
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#else
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#define VIRTUAL(address) (address)
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#endif
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#ifdef ASSEMBLY
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/**
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@ -24,7 +57,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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* @v function C function
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*/
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.macro virtcall function
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pushl $\function
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pushl $VIRTUAL(\function)
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call prot_call
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.endm
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@ -42,7 +75,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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* @v function C function
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*/
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#define VIRT_CALL( function ) \
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"pushl $( " #function " )\n\t" \
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"pushl $( " _S2 ( VIRTUAL ( function ) ) " )\n\t" \
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"call prot_call\n\t"
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/* Variables in librm.S */
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@ -19,8 +19,22 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )
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#define SIZEOF_REAL_MODE_REGS ( SIZEOF_I386_SEG_REGS + SIZEOF_I386_REGS )
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#define SIZEOF_I386_FLAGS 4
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#define SIZEOF_I386_ALL_REGS ( SIZEOF_REAL_MODE_REGS + SIZEOF_I386_FLAGS )
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.arch i386
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/* Size of an address */
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#ifdef __x86_64__
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#define SIZEOF_ADDR 8
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#else
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#define SIZEOF_ADDR 4
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#endif
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/* Selectively assemble code for 32-bit/64-bit builds */
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#ifdef __x86_64__
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#define if32 if 0
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#define if64 if 1
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#else
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#define if32 if 1
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#define if64 if 0
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#endif
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/****************************************************************************
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* Global descriptor table
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@ -126,7 +140,7 @@ rm_sp: .word 0
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rm_ss: .word 0
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.section ".data.pm_esp", "aw", @progbits
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pm_esp: .long _estack
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pm_esp: .long VIRTUAL(_estack)
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/****************************************************************************
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* Virtual address offsets
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@ -137,9 +151,9 @@ pm_esp: .long _estack
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****************************************************************************
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*/
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.struct 0
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VA_VIRT_OFFSET: .space 4
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VA_TEXT16: .space 4
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VA_DATA16: .space 4
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VA_VIRT_OFFSET: .space SIZEOF_ADDR
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VA_TEXT16: .space SIZEOF_ADDR
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VA_DATA16: .space SIZEOF_ADDR
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VA_SIZE:
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.previous
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@ -168,7 +182,7 @@ virt_addrs: .space VA_SIZE
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* Parameters:
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* %cs : .text16 segment
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* %ds : .data16 segment
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* %edi : Physical base of protected-mode code (virt_offset)
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* %edi : Physical base of protected-mode code
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****************************************************************************
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*/
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.section ".text16.init_librm", "ax", @progbits
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@ -181,7 +195,9 @@ init_librm:
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pushl %edi
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/* Store rm_virt_offset and set up virtual_cs and virtual_ds segments */
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subl $VIRTUAL(_textdata), %edi
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movl %edi, rm_virt_offset
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.if64 ; setae (rm_virt_offset+4) ; .endif
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movl %edi, %eax
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movw $virtual_cs, %bx
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call set_seg_base
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@ -195,7 +211,7 @@ init_librm:
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shll $4, %eax
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movw $real_cs, %bx
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call set_seg_base
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subl %edi, %eax
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.if32 ; subl %edi, %eax ; .endif
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movl %eax, rm_text16
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/* Store rm_ds and rm_data16, set up real_ds segment and GDT base */
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@ -207,7 +223,7 @@ init_librm:
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call set_seg_base
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movl %eax, gdt_base
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addl $gdt, gdt_base
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subl %edi, %eax
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.if32 ; subl %edi, %eax ; .endif
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movl %eax, rm_data16
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/* Switch to protected mode */
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@ -221,7 +237,7 @@ init_librm_pmode:
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movw $REAL_DS, %ax
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movw %ax, %ds
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movl $rm_virt_addrs, %esi
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movl $virt_addrs, %edi
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movl $VIRTUAL(virt_addrs), %edi
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movl $( VA_SIZE / 4 ), %ecx
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rep movsl
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popw %ds
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@ -312,7 +328,7 @@ real_to_prot:
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movl %cr0, %eax
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orb $CR0_PE, %al
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movl %eax, %cr0
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data32 ljmp $VIRTUAL_CS, $r2p_pmode
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data32 ljmp $VIRTUAL_CS, $VIRTUAL(r2p_pmode)
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.section ".text.real_to_prot", "ax", @progbits
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.code32
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r2p_pmode:
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@ -323,15 +339,15 @@ r2p_pmode:
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movw %ax, %fs
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movw %ax, %gs
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movw %ax, %ss
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movl pm_esp, %esp
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movl VIRTUAL(pm_esp), %esp
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/* Load protected-mode interrupt descriptor table */
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lidt idtr
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lidt VIRTUAL(idtr)
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/* Record real-mode %ss:sp (after removal of data) */
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movw %bp, rm_ss
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movw %bp, VIRTUAL(rm_ss)
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addl %ecx, %edx
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movw %dx, rm_sp
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movw %dx, VIRTUAL(rm_sp)
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/* Move data from RM stack to PM stack */
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subl %ecx, %esp
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@ -365,7 +381,8 @@ r2p_pmode:
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.code32
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prot_to_real:
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/* Copy real-mode global descriptor table register to RM code segment */
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movl text16, %edi
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movl VIRTUAL(text16), %edi
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.if64 ; subl VIRTUAL(virt_offset), %edi ; .endif
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leal rm_gdtr(%edi), %edi
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movsw
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movsl
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@ -377,20 +394,20 @@ prot_to_real:
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addl $4, %ecx
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/* Real-mode %ss:sp => %ebp:edx and virtual address => %edi */
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movzwl rm_ss, %ebp
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movzwl rm_sp, %edx
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movzwl VIRTUAL(rm_ss), %ebp
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movzwl VIRTUAL(rm_sp), %edx
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subl %ecx, %edx
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movl %ebp, %eax
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shll $4, %eax
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leal (%eax,%edx), %edi
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subl virt_offset, %edi
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subl VIRTUAL(virt_offset), %edi
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/* Move data from PM stack to RM stack */
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movl %esp, %esi
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rep movsb
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/* Record protected-mode %esp (after removal of data) */
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movl %esi, pm_esp
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movl %esi, VIRTUAL(pm_esp)
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/* Load real-mode segment limits */
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movw $P2R_DS, %ax
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@ -512,7 +529,7 @@ prot_call:
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/* Switch to protected mode and move register dump to PM stack */
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movl $PC_OFFSET_END, %ecx
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pushl $pc_pmode
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pushl $VIRTUAL(pc_pmode)
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jmp real_to_prot
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.section ".text.prot_call", "ax", @progbits
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.code32
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@ -589,7 +606,7 @@ real_call:
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/* Switch to real mode and move register dump to RM stack */
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movl $( RC_OFFSET_REGS_END + 4 /* function pointer copy */ ), %ecx
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pushl $rc_rmode
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movl $rm_default_gdtr_idtr, %esi
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movl $VIRTUAL(rm_default_gdtr_idtr), %esi
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jmp prot_to_real
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.section ".text16.real_call", "ax", @progbits
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.code16
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@ -605,7 +622,7 @@ rc_rmode:
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/* Switch to protected mode and move register dump back to PM stack */
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movl $RC_OFFSET_REGS_END, %ecx
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pushl $rc_pmode
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pushl $VIRTUAL(rc_pmode)
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jmp real_to_prot
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.section ".text.real_call", "ax", @progbits
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.code32
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@ -665,6 +682,8 @@ flatten_dummy:
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* May be entered with either physical or virtual stack segment.
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****************************************************************************
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*/
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.section ".text.interrupt_wrapper", "ax", @progbits
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.code32
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.globl interrupt_wrapper
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interrupt_wrapper:
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/* Preserve segment registers and original %esp */
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@ -7,10 +7,6 @@ CFLAGS += -fstrength-reduce -fomit-frame-pointer
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#
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CFLAGS += -falign-jumps=1 -falign-loops=1 -falign-functions=1
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# Use %rip-relative addressing wherever possible.
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#
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CFLAGS += -fpie
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# Force 64-bit code
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#
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CFLAGS += -m64
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@ -1,5 +1,9 @@
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# -*- makefile -*- : Force emacs to use Makefile mode
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# Use %rip-relative addressing wherever possible.
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#
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CFLAGS += -fpie
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# EFI probably doesn't guarantee us a red zone, so let's not rely on it.
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#
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CFLAGS += -mno-red-zone
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@ -1,5 +1,14 @@
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# -*- makefile -*- : Force emacs to use Makefile mode
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# Place .textdata in negative 2GB of address space
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#
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CFLAGS += -mcmodel=kernel
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LDFLAGS += --section-start=.textdata=0xffffffffeb000000
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# Assembly code does not respect a red zone.
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#
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CFLAGS += -mno-red-zone
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# Include generic BIOS Makefile
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#
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MAKEDEPS += arch/x86/Makefile.pcbios
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