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FABRIC.md: item 4.5d -- Finding 3 (muldiv64) root-caused and fixed via QEMU tracing, Finding 4 blocks

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Used QEMU-side instrumentation (-d int tracing, plus a working chardev-based
monitor -- the older bareword -monitor syntax silently fails on QEMU
10.2.1) as directed. The PM Timer "stall" was never a hang: it was a #DE
divide error cascading to a triple fault, which -no-reboot converts into a
silent clean QEMU exit -- indistinguishable from a hang without tracing,
and why arch_relax() (solving a hang that didn't exist) had no effect.
Root cause and fix documented in full (also see commit b43e51a).

With the fix, amd64 boot at -O2 now proceeds far past the original stall --
through capsule birth and into Hermes's word registration -- before hitting
a second, different fault (Finding 4): a direct #GP at IDT index 32
(APIC_TIMER_VECTOR), not yet root-caused. Same silent-triple-fault-exit
shape, so this was very likely bundled into "the hang" before tracing
distinguished the two separate bugs.

-O2 reverted again (uncommitted); muldiv64's fix is kept, real and
independently verified at unchanged -O0 on all three architectures.
Routine three-arch artifacts from this session's verification runs
included.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Robert Allan James
2026-08-11 12:17:23 -04:00
co-authored by Claude Sonnet 5
parent b43e51a95d
commit 1c5e926c3f
18 changed files with 104344 additions and 77 deletions
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experiments/bare_metal/latest/amd64.csv
+22 -22
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@@ -84,27 +84,27 @@ tick_number,elapsed_ns,tick_interval_ns,cache_hits_delta,bucket_hits_delta,word_
10,100000,10000,0,0,256,36,11,4096,978,0,0,44,65536,0,0,65536,0,0
11,110000,10000,0,0,256,36,11,4096,1234,0,0,50,65536,0,0,65536,0,0
12,120000,10000,0,0,256,36,12,4096,1490,0,0,56,65536,0,0,65536,0,0
13,130000,10000,0,0,256,37,12,4096,1746,0,0,62,65536,0,0,65536,0,0
14,140000,10000,0,0,230,39,12,4096,1949,0,0,68,65536,0,0,65536,0,0
13,130000,10000,0,0,256,37,12,4096,1746,0,0,63,65536,0,0,65536,0,0
14,140000,10000,0,0,230,39,12,4096,1949,0,0,69,65536,0,0,65536,0,0
15,150000,10000,0,0,256,39,13,4096,2204,0,0,75,65536,0,0,65536,0,0
16,160000,10000,0,0,256,39,14,4096,2459,0,0,81,65536,0,0,65536,0,0
17,170000,10000,0,0,256,39,15,4096,2713,0,0,87,65536,0,0,65536,0,0
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19,190000,10000,0,0,256,39,16,4096,3224,0,0,99,65536,0,1,65536,0,0
20,200000,10000,0,0,256,41,17,4096,3480,0,0,106,65536,0,1,65536,0,0
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25,250000,10000,0,0,256,43,20,2048,2048,0,0,139,65536,0,1,65536,0,0
26,260000,10000,0,0,256,45,21,2048,2048,0,0,145,65536,0,1,65536,0,0
27,270000,10000,0,0,256,45,22,1024,1024,0,0,151,65536,0,1,65536,0,0
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31,310000,10000,0,0,256,45,25,256,256,0,0,176,65536,0,1,65536,0,0
32,320000,10000,0,0,255,45,26,256,256,0,0,182,65536,0,1,65536,0,0
33,330000,10000,0,0,256,45,27,256,256,0,0,188,65536,0,1,65536,0,0
34,340000,10000,0,0,256,45,27,256,256,0,0,194,65536,0,1,65536,0,0
35,350000,10000,0,0,256,45,28,256,256,0,0,201,65536,0,1,65536,0,0
36,360000,10000,0,0,256,45,29,256,256,0,0,207,65536,0,1,65536,0,0
17,170000,10000,0,0,256,39,15,4096,2713,0,0,88,65536,0,0,65536,0,0
18,180000,10000,0,0,256,39,15,4096,2969,0,0,94,65536,0,0,65536,0,0
19,190000,10000,0,0,256,39,16,4096,3224,0,0,100,65536,0,1,65536,0,0
20,200000,10000,0,0,256,41,17,4096,3480,0,0,107,65536,0,1,65536,0,0
21,210000,10000,0,0,256,41,17,4096,3736,0,0,113,65536,0,1,65536,0,0
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32,320000,10000,0,0,255,45,26,256,256,0,0,185,65536,0,1,65536,0,0
33,330000,10000,0,0,256,45,27,256,256,0,0,192,65536,0,1,65536,0,0
34,340000,10000,0,0,256,45,27,256,256,0,0,198,65536,0,1,65536,0,0
35,350000,10000,0,0,256,45,28,256,256,0,0,204,65536,0,1,65536,0,0
36,360000,10000,0,0,256,45,29,256,256,0,0,210,65536,0,1,65536,0,0
1 tick_number elapsed_ns tick_interval_ns cache_hits_delta bucket_hits_delta word_executions_delta hot_word_count avg_word_heat_q48 window_width actual_window_size predicted_label_hits jitter_bits apic_ticks time_trust_q48 variance_q48 vm_call_depth_max hera_heat_q48 hermes_heat_q48 artemis_heat_q48
84 10 100000 10000 0 0 256 36 11 4096 978 0 0 44 65536 0 0 65536 0 0
85 11 110000 10000 0 0 256 36 11 4096 1234 0 0 50 65536 0 0 65536 0 0
86 12 120000 10000 0 0 256 36 12 4096 1490 0 0 56 65536 0 0 65536 0 0
87 13 130000 10000 0 0 256 37 12 4096 1746 0 0 62 63 65536 0 0 65536 0 0
88 14 140000 10000 0 0 230 39 12 4096 1949 0 0 68 69 65536 0 0 65536 0 0
89 15 150000 10000 0 0 256 39 13 4096 2204 0 0 75 65536 0 0 65536 0 0
90 16 160000 10000 0 0 256 39 14 4096 2459 0 0 81 65536 0 0 65536 0 0
91 17 170000 10000 0 0 256 39 15 4096 2713 0 0 87 88 65536 0 0 65536 0 0
92 18 180000 10000 0 0 256 39 15 4096 2969 0 0 93 94 65536 0 0 65536 0 0
93 19 190000 10000 0 0 256 39 16 4096 3224 0 0 99 100 65536 0 1 65536 0 0
94 20 200000 10000 0 0 256 41 17 4096 3480 0 0 106 107 65536 0 1 65536 0 0
95 21 210000 10000 0 0 256 41 17 4096 3736 0 0 112 113 65536 0 1 65536 0 0
96 22 220000 10000 0 0 256 41 18 4096 3992 0 0 120 122 65536 0 1 65536 0 0
97 23 230000 10000 0 0 256 41 19 4096 4096 0 0 126 128 65536 0 1 65536 0 0
98 24 240000 10000 0 0 256 41 20 4096 4096 0 0 132 134 65536 0 1 65536 0 0
99 25 250000 10000 0 0 256 43 20 2048 2048 0 0 139 141 65536 0 1 65536 0 0
100 26 260000 10000 0 0 256 45 21 2048 2048 0 0 145 147 65536 0 1 65536 0 0
101 27 270000 10000 0 0 256 45 22 1024 1024 0 0 151 153 65536 0 1 65536 0 0
102 28 280000 10000 0 0 256 45 23 1024 1024 0 0 157 160 65536 0 1 65536 0 0
103 29 290000 10000 0 0 256 45 24 512 512 0 0 164 166 65536 0 1 65536 0 0
104 30 300000 10000 0 0 256 45 24 512 512 0 0 170 173 65536 0 1 65536 0 0
105 31 310000 10000 0 0 256 45 25 256 256 0 0 176 179 65536 0 1 65536 0 0
106 32 320000 10000 0 0 255 45 26 256 256 0 0 182 185 65536 0 1 65536 0 0
107 33 330000 10000 0 0 256 45 27 256 256 0 0 188 192 65536 0 1 65536 0 0
108 34 340000 10000 0 0 256 45 27 256 256 0 0 194 198 65536 0 1 65536 0 0
109 35 350000 10000 0 0 256 45 28 256 256 0 0 201 204 65536 0 1 65536 0 0
110 36 360000 10000 0 0 256 45 29 256 256 0 0 207 210 65536 0 1 65536 0 0