MIPSのブートについて理解するためには、まずはMIPSアーキテクチャのメモリマップについて理解しなければ。
このあたりに、メモリマップの説明がある。
ファイル:MIPS32 MemoryMap.png - Wikipedia
これを見ると、0xA000_0000-0xBFFF_FFFF, 0x8000_0000-0x9FFF_FFFF は実際には物理メモリの0x0000_0000からマップされるようになっているらしい。
Each Segment of an Address Space is classified as “Mapped” or “Unmapped”. A “Mapped” address is one that is translated through the TLB or other address translation unit. An “Unmapped” address is one which is not translated through the TLB and which provides a window into the lowest portion of the physical address space, starting at physical address zero, and with a size corresponding to the size of the unmapped Segment. Additionally, the kseg1 Segment is classified as “Uncached”. References to this Segment bypass all levels of the cache hierarchy and allow direct access to memory without any interference from the caches
つまり、kseg0とkseg1は、問答無用で0x0000_0000にマップしても良いということか。
mips_env.cpp に仮想アドレスから物理アドレスに変換する関数を追加した。
Addr_t MipsEnv::ConvertVirtualAddress (Addr_t vaddr)
{
if (0x80000000 <= vaddr && vaddr <= 0x9fffffff) {
return vaddr - 0x80000000;
} else if (0xA0000000 <= vaddr && vaddr <= 0xbfffffff) {
return vaddr - 0xa0000000;
} else {
return vaddr;
}
}
実行すると、仮想アドレスと物理アドレスを両方表示するようにしておく。
<Load Image /home/vagrant/xv6-mips/xv6.img>
<Info: NewMemory Region 1fc00000 is defined.>
0 : [Vbfc00000:P1fc00000] 40086000 : mfc0 r12,0x0c,0x0 Wired=>00007ffd r08<=00007ffd
1 : [Vbfc00004:P1fc00004] 24090001 : addiu r09,r00,0x0001 r00=>00000000 r09<=00000001
2 : [Vbfc00008:P1fc00008] 01294025 : or r08,r09,r09 r09=>00000001 r09=>00000001 r08<=00000001
3 : [Vbfc0000c:P1fc0000c] 01094026 : xor r08,r08,r09 r08=>00000001 r09=>00000001 r08<=00000000
4 : [Vbfc00010:P1fc00010] 3508ff00 : ori r08,r08,0xff00 r08=>00000000 r08<=0000ff00
5 : [Vbfc00014:P1fc00014] 3c091000 : lui r09,0x1000 r09<=10000000
6 : [Vbfc00018:P1fc00018] 01094025 : or r08,r08,r09 r08=>0000ff00 r09=>10000000 r08<=1000ff00
7 : [Vbfc0001c:P1fc0001c] 40886000 : mtc0 r12,0x0c,0x0 r08=>1000ff00 Wired<=1000ff00
8 : [Vbfc00020:P1fc00020] 3c1d1fc0 : lui r29,0x1fc0 r29<=1fc00000
9 : [Vbfc00024:P1fc00024] 27bd0000 : addiu r29,r29,0x0000 r29=>1fc00000 r29<=1fc00000
10 : [Vbfc00028:P1fc00028] 3c181fc0 : lui r24,0x1fc0 r24<=1fc00000
11 : [Vbfc0002c:P1fc0002c] 27180124 : addiu r24,r24,0x0124 r24=>1fc00000 r24<=1fc00124
12 : [Vbfc00030:P1fc00030] 0300f809 : jalr r24,r31 r24=>1fc00124 r31<=bfc00038 pc<=bfc00034 pc<=1fc00124
13 : [Vbfc00034:P1fc00034] 00000000 : sll r00,r00,0x00 r00=>00000000
14 : [V1fc00124:P1fc00124] 27bdffe8 : addiu r29,r29,0xffe8 r29=>1fc00000 r29<=1fbfffe8
15 : [V1fc00128:P1fc00128] 3c040001 : lui r04,0x0001 r04<=00010000
16 : [V1fc0012c:P1fc0012c] 00003021 : addu r06,r00,r00 r00=>00000000 r00=>00000000 r06<=00000000
17 : [V1fc00130:P1fc00130] afbf0014 : sw r31,0x0014(r31) r29=>1fbfffe8 r31=>bfc00038 (1fbffffc)<=bfc00038
18 : [V1fc00134:P1fc00134] 0ff00037 : jal 0x3f00037 r31<=1fc0013c pc<=1fc00138 pc<=1fc000dc
19 : [V1fc00138:P1fc00138] 24051000 : addiu r05,r00,0x1000 r00=>00000000 r05<=00001000
20 : [V1fc000dc:P1fc000dc] 27bdffe8 : addiu r29,r29,0xffe8 r29=>1fbfffe8 r29<=1fbfffd0
21 : [V1fc000e0:P1fc000e0] 30c901ff : andi r09,r06,0x01ff r06=>00000000 r09<=00000000
22 : [V1fc000e4:P1fc000e4] 00063242 : srl r06,r06,0x09 r06=>00000000 r06<=00000000
23 : [V1fc000e8:P1fc000e8] 00855021 : addu r10,r04,r05 r04=>00010000 r05=>00001000 r10<=00011000
24 : [V1fc000ec:P1fc000ec] afbf0014 : sw r31,0x0014(r31) r29=>1fbfffd0 r31=>1fc0013c (1fbfffe4)<=1fc0013c
25 : [V1fc000f0:P1fc000f0] 00894823 : subu r09,r04,r09 r04=>00010000 r09=>00000000 r09<=00010000
26 : [V1fc000f4:P1fc000f4] 24c80001 : addiu r08,r06,0x0001 r06=>00000000 r08<=00000001
27 : [V1fc000f8:P1fc000f8] 012a102b : sltu r02,r09,r10 r09=>00010000 r10=>00011000 r02<=00000001
28 : [V1fc000fc:P1fc000fc] 10400006 : beq r02,r00,0x0006 r02=>00000001 r00=>00000000 pc<=1fc00100
29 : [V1fc00100:P1fc00100] 01002821 : addu r05,r08,r00 r08=>00000001 r00=>00000000 r05<=00000001
まずはここまで、シンプルな
