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starkernel: fix lidt() inline-asm constraint hazard, land -O2

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FABRIC.md item 4.5d Finding 4: lidt()'s inline asm used a register-only
("r") constraint on the idtr pointer, never telling GCC the asm
dereferences the pointee. At -O2 this let the compiler treat the
256-entry idt[] population loop and idtr_desc's field writes as dead
stores and eliminate them entirely, loading IDTR from uninitialized
stack instead of the real table -- a #GP on the first APIC timer tick
that happened to land on garbage. Same bug class as the earlier
muldiv64 fix (b43e51a): an inline-asm constraint too weak for what the
asm actually touches, invisible at -O0, live at -O2.

Fixed by switching to a memory operand ("m"(*idtr_desc)), matching how
Linux's own load_idt() is written. aarch64/riscv64 checked for the same
pattern -- neither has it, both install their vector/trap tables
entirely in hand-written .S.

Verified: all three architectures boot clean to ok>, POST Failed: 0,
identical dict-hashes across all three under -O2, zero new warnings
vs an -O0 baseline (amd64 3040/3040, aarch64 3041/3041 serial,
riscv64 3037/3037). -O2/-U_FORTIFY_SOURCE landed permanently in
COMMON_CFLAGS.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Robert Allan James
2026-08-11 16:57:20 -04:00
co-authored by Claude Sonnet 5
parent 065ab50240
commit a1c9fc7330
13 changed files with 54912 additions and 87 deletions
Download Patch File Download Diff File Expand all files Collapse all files
experiments/bare_metal/latest/amd64.csv
+36 -36
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@@ -72,39 +72,39 @@ tick_number,elapsed_ns,tick_interval_ns,cache_hits_delta,bucket_hits_delta,word_
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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
72 71 710000 10000 0 0 44 22 39 4096 1757 0 0 0 65536 0 0 65536 0 0
73 72 720000 10000 0 0 130 24 27 4096 1757 0 0 0 65536 0 0 65536 0 0
74 73 730000 10000 0 0 134 26 21 4096 1757 0 0 0 65536 0 0 65536 0 0
75 1 10000 18446744073708831616 0 0 117 4 4 4096 0 0 4895412794951728796 13 5 65536 0 0 65536 0 0
76 2 20000 10000 0 0 78 10 7 4096 0 0 0 15 7 65536 0 0 65536 0 0
77 3 30000 10000 0 0 101 13 7 4096 0 0 0 16 8 65536 0 0 65536 0 0
78 4 40000 10000 0 0 63 19 8 4096 0 0 0 17 9 65536 0 0 65536 0 0
79 5 50000 10000 0 0 92 25 8 4096 2 0 0 20 11 65536 0 0 65536 0 0
80 6 60000 10000 0 0 64 27 8 4096 2 0 0 21 11 65536 0 0 65536 0 0
81 7 70000 10000 0 0 228 32 8 4096 210 0 0 27 16 65536 0 0 65536 0 0
82 8 80000 10000 0 0 256 34 9 4096 466 0 0 34 22 65536 0 0 65536 0 0
83 9 90000 10000 0 0 256 36 10 4096 722 0 0 40 27 65536 0 0 65536 0 0
84 10 100000 10000 0 0 256 36 11 4096 978 0 0 46 32 65536 0 0 65536 0 0
85 11 110000 10000 0 0 256 36 11 4096 1234 0 0 53 38 65536 0 0 65536 0 0
86 12 120000 10000 0 0 256 36 12 4096 1490 0 0 59 43 65536 0 0 65536 0 0
87 13 130000 10000 0 0 256 37 12 4096 1746 0 0 65 48 65536 0 0 65536 0 0
88 14 140000 10000 0 0 230 39 12 4096 1949 0 0 71 53 65536 0 0 65536 0 0
89 15 150000 10000 0 0 256 39 13 4096 2204 0 0 78 58 65536 0 0 65536 0 0
90 16 160000 10000 0 0 256 39 14 4096 2459 0 0 84 64 65536 0 0 65536 0 0
91 17 170000 10000 0 0 256 39 15 4096 2713 0 0 91 69 65536 0 0 65536 0 0
92 18 180000 10000 0 0 256 39 15 4096 2969 0 0 97 74 65536 0 0 65536 0 0
93 19 190000 10000 0 0 256 39 16 4096 3224 0 0 104 80 65536 0 1 65536 0 0
94 20 200000 10000 0 0 256 41 17 4096 3480 0 0 111 85 65536 0 1 65536 0 0
95 21 210000 10000 0 0 256 41 17 4096 3736 0 0 117 90 65536 0 1 65536 0 0
96 22 220000 10000 0 0 256 41 18 4096 3992 0 0 127 95 65536 0 1 65536 0 0
97 23 230000 10000 0 0 256 41 19 4096 4096 0 0 133 102 65536 0 1 65536 0 0
98 24 240000 10000 0 0 256 41 20 4096 4096 0 0 140 107 65536 0 1 65536 0 0
99 25 250000 10000 0 0 256 43 20 2048 2048 0 0 146 113 65536 0 1 65536 0 0
100 26 260000 10000 0 0 256 45 21 2048 2048 0 0 152 118 65536 0 1 65536 0 0
101 27 270000 10000 0 0 256 45 22 1024 1024 0 0 159 123 65536 0 1 65536 0 0
102 28 280000 10000 0 0 256 45 23 1024 1024 0 0 165 129 65536 0 1 65536 0 0
103 29 290000 10000 0 0 256 45 24 512 512 0 0 171 134 65536 0 1 65536 0 0
104 30 300000 10000 0 0 256 45 24 512 512 0 0 178 139 65536 0 1 65536 0 0
105 31 310000 10000 0 0 256 45 25 256 256 0 0 184 145 65536 0 1 65536 0 0
106 32 320000 10000 0 0 255 45 26 256 256 0 0 190 150 65536 0 1 65536 0 0
107 33 330000 10000 0 0 256 45 27 256 256 0 0 197 155 65536 0 1 65536 0 0
108 34 340000 10000 0 0 256 45 27 256 256 0 0 203 161 65536 0 1 65536 0 0
109 35 350000 10000 0 0 256 45 28 256 256 0 0 209 166 65536 0 1 65536 0 0
110 36 360000 10000 0 0 256 45 29 256 256 0 0 215 172 65536 0 1 65536 0 0