code wiki / _hdl_build / nx_emu_x86_farjmp_test.nx
`nx_emu_x86_farjmp_test.nx` source

1// nx_emu_x86_farjmp_test.nx -- x86 full-system ladder R5 rung-5: PROTECTED-MODE ENTRY (GDT + selector
2// + far-jump).  After CR0.PE=1, the boot does `ljmp 0x08:entry`: the selector (0x08) indexes the GDT
3// (index = sel >> 3), the descriptor gives the segment BASE, and the CPU resumes 32-bit execution at
4// base+offset (linear).  This models that resolution: selector -> GDT base -> linear far-jump target.
5// KAT: flat GDT (entry1 base=0, entry2 base=1MB); selector/index extraction; far-jump targets.
6// HONEST SCOPE: base-direct descriptor model + the resolution; the real 8-byte GDT descriptor packing
7// (base split / limit / access / granularity) + the EA-opcode decode = refinements.  R5 rung-6 = wire
8// real-mode+seg:off+PE+far-jump into ONE end-to-end "boot to protected mode" run.  No hardware writes
9// (Rule 26).  expect_exit: 0   license_tier: ORIGINAL
10import "nx_syscalls.nx"
11
12func fj_puts(s: *u8) -> i64 { var n: i64=0; while s[n]!=(0 as u8){n=n+1} sys_write(1,s,n); return 0 }
13func fj_num(v: i64) -> i64 { let b: *u8=sys_mmap(28); var m: i64=v; if m<0{m=0-m;sys_write(1,"-" as *u8,1)} let t: *u8=sys_mmap(28); var k: i64=0; if m==0{t[0]=48 as u8;k=1} while m>0{t[k]=(48+(m%10)) as u8;m=m/10;k=k+1} var i: i64=0; while i<k{b[i]=t[k-1-i];i=i+1} sys_write(1,b,k); return 0 }
14
15// selector -> GDT index (top 13 bits; low 3 = RPL/TI).
16func sel_index(sel: i64) -> i64 { return sel >> 3 }
17// resolve a selector to its segment base via the GDT (base-direct model).
18func gdt_base(gdt: *i64, sel: i64) -> i64 { return gdt[sel >> 3] }
19// far-jump linear target = segment base (from selector) + offset.
20func far_target(gdt: *i64, sel: i64, off: i64) -> i64 { return gdt_base(gdt, sel) + off }
21
22func main() -> i64 {
23    fj_puts("x86 full-system ladder R5 rung-5: PROTECTED-MODE ENTRY (GDT + selector + far-jump)\n" as *u8)
24    let gdt: *i64 = sys_mmap(8 * 16) as *i64
25    gdt[0] = 0           // null descriptor
26    gdt[1] = 0           // selector 0x08: flat 32-bit code, base 0
27    gdt[2] = 0x100000    // selector 0x10: base = 1 MB
28
29    var pass: i64=0
30    var ttl: i64=0
31
32    ttl=ttl+1; fj_puts("  T1 selector 0x08 -> GDT index " as *u8); fj_num(sel_index(0x08)); fj_puts(" (want 1): " as *u8); if sel_index(0x08)==1 { pass=pass+1; fj_puts("PASS\n" as *u8) } else { fj_puts("FAIL\n" as *u8) }
33    ttl=ttl+1; fj_puts("  T2 selector 0x10 -> GDT index " as *u8); fj_num(sel_index(0x10)); fj_puts(" (want 2): " as *u8); if sel_index(0x10)==2 { pass=pass+1; fj_puts("PASS\n" as *u8) } else { fj_puts("FAIL\n" as *u8) }
34
35    let t3: i64 = far_target(gdt, 0x08, 0x1000)
36    ttl=ttl+1; fj_puts("  T3 ljmp 0x08:0x1000 (flat) -> linear " as *u8); fj_num(t3); fj_puts(" (want 4096): " as *u8); if t3==0x1000 { pass=pass+1; fj_puts("PASS\n" as *u8) } else { fj_puts("FAIL\n" as *u8) }
37
38    let t4: i64 = far_target(gdt, 0x08, 0x7C00)
39    ttl=ttl+1; fj_puts("  T4 ljmp 0x08:0x7C00 (boot code, now protected) -> " as *u8); fj_num(t4); fj_puts(" (want 31744): " as *u8); if t4==0x7C00 { pass=pass+1; fj_puts("PASS\n" as *u8) } else { fj_puts("FAIL\n" as *u8) }
40
41    let t5: i64 = far_target(gdt, 0x10, 0x0010)
42    ttl=ttl+1; fj_puts("  T5 ljmp 0x10:0x0010 (base=1MB) -> " as *u8); fj_num(t5); fj_puts(" (want 1048592=0x100010): " as *u8); if t5==0x100010 { pass=pass+1; fj_puts("PASS\n" as *u8) } else { fj_puts("FAIL\n" as *u8) }
43
44    fj_puts("X86-FARJMP-GATE passed " as *u8); fj_num(pass); fj_puts("/" as *u8); fj_num(ttl)
45    if pass==ttl { fj_puts(" verdict=GREEN (protected-mode entry: selector->GDT base->linear; end-to-end boot-to-protected = R5 rung-6)\n" as *u8); sys_exit(0); return 0 }
46    fj_puts(" verdict=RED\n" as *u8); sys_exit(1); return 1
47}
nx_emu_x86_farjmp_test.nx source

`nx_emu_x86_farjmp_test.nx` source
