vap/assembly/ppc32/get_real.S

.section .text

.global vap_get_real
vap_get_real:
    // switches the kernel from relying on openfirmware's virtual memory
    // to its own BAT-mapped memory
    // r3 = "translation table" (array of addresses of physical pages, starting at the virtual page with address 0)
    // r4 = "translation table" size (in pages)
    // r5 = vap_get_fake
    // r6 = so_fake (pointer to the function to call after the kernel has been remapped (IN VIRTUAL MEMORY))
    // r7 = amount of memory this system has (in bytes)
    // r8 = stack pointer (IN VIRTUAL MEMORY)
    // all pointer arguments are physical addresses unless otherwise specified

    // disable interrupts
    mfmsr 31
    rlwinm 31, 31, 0, 17, 15
    mtmsr 31

    // enter real mode
    mtsrr0 5
    mfmsr 31
    li 31, (1 << ((32-1) - 19))
    mtmsr 31

    // now we can rfi to so_real
    sync
    isync
.global vap_get_fake
.extern VAP_KERN_BASE
.extern VAP_KERN_PHOF
.extern VAP_KERN_END
vap_get_fake:
    // we are now in actual real mode, the registers shouldn't have changed

    // for the first 256MiB, virtual=physical

    // normally i'd write register names as their true values, but with the bat registers
    // that'd just make things purely unreadable
    #define ibat0u   528
    #define ibat0l   529
    #define ibat1u   530
    #define ibat1l   531
    #define ibat2u   532
    #define ibat2l   533
    #define ibat3u   534
    #define ibat3l   535
    #define dbat0u   536
    #define dbat0l   537
    #define dbat1u   538
    #define dbat1l   539
    #define dbat2u   540
    #define dbat2l   541
    #define dbat3u   542
    #define dbat3l   543

    // here we will give all of the bat registers an initial value of 0
    li 30, 0
    mtspr ibat0u, 30
    mtspr ibat0l, 30
    mtspr ibat1u, 30
    mtspr ibat1l, 30
    mtspr ibat2u, 30
    mtspr ibat2l, 30
    mtspr ibat3u, 30
    mtspr ibat3l, 30
    mtspr dbat0u, 30
    mtspr dbat0l, 30
    mtspr dbat1u, 30
    mtspr dbat1l, 30
    mtspr dbat2u, 30
    mtspr dbat2l, 30
    mtspr dbat3u, 30
    mtspr dbat3l, 30

    // now we can set up the bat registers
    li 7, ((0x7FF<<2)|2)
    li 8, ((2<<3)|2)

    sync
    isync

    mtspr dbat0u, 7
    mtspr dbat0l, 8
    sync
    isync
    mtspr ibat0u, 7
    mtspr ibat0l, 8
    sync
    isync

    // zero the rest


    finish_bat:
    // theoretically, we should be done with the bat registers now

    // we can now rfi to so_real (who's address should still be in r6)
    // this function is in virtual memory, but this shouldn't matter as we have set up the bat registers
    // to map said virtual memory to the same physical memory
    mtsrr0 6

    // we need to set the srr1 register to the value of the msr register
    // but also re-enable MSR_IR and MSR_DR so that we can use the bat registers
    mfmsr 31
    li 31, ((1 << ((32-1) - 19)) | (1 << ((32-1) - 26)) | (1 << ((32-1) - 27)))
    // enable bit 30 to allow system resets to be recoverable
    mtsrr1 31

    //mr 1, 8 // restore the stack pointer

    // now we can rfi to so_real
    sync
    isync
    rfi

.extern finalize_bootstrapping
.global so_fake
// this is the function that we will rfi to
so_fake:
    //li 0, 0 // load 0 into r0
    //// make sure the pointer is aligned to 16 bytes to grow downwards
    //addi 1, 1, 0xf
    //// store r0 into the stack
    //stw 0, 0(1)
    //stwu 1, -32(1) // new stack frame
    lis 3, finalize_bootstrapping@ha // load the address of finalize_bootstrapping into r3
    ori 3, 3, finalize_bootstrapping@l // load the address of finalize_bootstrapping into r3
    mtlr 3 // load the address of finalize_bootstrapping into the link register
    blrl // call finalize_bootstrapping


.section VAP_STACK_SECTION, "aw", @progbits
.global VAP_STACK
.align 4
.space 0x2000
VAP_STACK: