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d2r2: when deduplicating types, ensure deterministic (hash -> .debug_info off) mapping, by minimizing the .debug_info off found for a particular type hash - in theory, this step should not be necessary, but there is a mistake / broken part of this theory, which was leading to non-deterministic type graphs in a very small # of cases, due to the same hash mapping to different .debug_info offsets across runs. in theory, the hash itself should take care of this, but there is likely something important missing. in either case, minimizing the .debug_info offset is very cheap, and guarantees we parse from a deterministic place no matter what the run looks like.

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This commit is contained in:
Ryan Fleury
2026-05-02 20:25:33 -07:00
parent f9eb25dbcb
commit 4f3d9c96b8
2 changed files with 71 additions and 24 deletions
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src/rdi_from_dwarf/rdi_from_dwarf_2.c
+71 -23
View File
@@ -7,7 +7,7 @@
internal int
d2r2_unique_type_tag_node_is_less_than(D2R2_UniqueTypeTagNode **l, D2R2_UniqueTypeTagNode **r)
{
int is_less_than = l[0]->hash < r[0]->hash;
int is_less_than = (l[0]->hash < r[0]->hash);
return is_less_than;
}
@@ -169,6 +169,7 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
}
}
lane_sync();
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
////////////////////////////
//- rjf: parse all units from .debug_aranges
@@ -1685,7 +1686,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
dependency_task->unit_idx = t->unit_idx;
if(!contains_1u64(unit_info_tag_range, dependency_task->off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, dependency_task->off);
if(0 < new_unit_num && new_unit_num <= unit_count)
{
@@ -1748,15 +1748,61 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
U64 slot_head_val = (U64)ins_atomic_u64_eval(&unique_type_tag_slots[slot_idx]);
// rjf: determine if this hash has been gathered
D2R2_UniqueTypeTagNode *already_gathered_node = 0;
for(D2R2_UniqueTypeTagNode *n = (D2R2_UniqueTypeTagNode *)slot_head_val; n != 0; n = n->next)
{
if(n->hash == hash)
{
gathered = 1;
already_gathered_node = n;
break;
}
}
// rjf: if this hash *has* been gathered, we want to prefer a
// deterministic unit/info offset - so we'll just prefer the
// lowest unit/offset.
//
// TODO(rjf): this seems to only be necessary because of a flaw
// in the deduplicator logic (without this part). in theory, if we
// trust the hash (all experiments suggested that we should - e.g.
// no hash collisions w/ different data were observed), then the
// same hash should imply an identical type graph. this may be false
// for reasons I do not currently understand, or due to a mistake
// somewhere. but for now, I've added this, to ensure that when there
// are many type tag trees which map to an identical hash, we always
// parse the one from the lowest .debug_info offset, just to make
// sure it's deterministic. in a multi-threaded conversion, this
// is not true in general without this step; one thread which finds
// the same type with a higher .debug_info offset may win, and so
// where exactly one type hash is parsed is not deterministic. but,
// the theory is, that shouldn't matter - the type graphs should
// match nonetheless. in any case, if that turns out to be a broken
// theory, this should be a relatively cheap step to guarantee
// deterministic (hash -> .debug_info offset), which is likely a
// desirable property regardless. but I wanted to leave this here
// so that I can more closely verify what is going on later.
//
if(gathered && already_gathered_node != 0)
{
B32 minimized = 0;
for(;!minimized;)
{
U64 stored_info_off = ins_atomic_u64_eval(&already_gathered_node->info_off);
if(start_off < stored_info_off)
{
if(ins_atomic_u64_eval_cond_assign(&already_gathered_node->info_off, start_off, stored_info_off) == stored_info_off)
{
minimized = 1;
}
}
else
{
minimized = 1;
}
}
}
// rjf: if this hash has *not* been gathered, try an insert. we:
//
// 1. allocate/fill a node
@@ -1771,7 +1817,7 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
D2R2_UniqueTypeTagNode *n = push_array(scratch.arena, D2R2_UniqueTypeTagNode, 1);
n->next = (D2R2_UniqueTypeTagNode *)slot_head_val;
n->hash = hash;
n->unit_idx = origin_unit_idx;
// n->unit_idx = origin_unit_idx;
n->info_off = start_off;
U64 new_head_val = (U64)n;
if(slot_head_val == ins_atomic_u64_eval_cond_assign(&unique_type_tag_slots[slot_idx], new_head_val, slot_head_val))
@@ -1829,8 +1875,8 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
}
}
}
lane_sync();
}
lane_sync();
}
////////////////////////////
@@ -1971,7 +2017,8 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
if(type_tag_node != 0)
{
info_off = type_tag_node->info_off;
unit_idx = type_tag_node->unit_idx;
U64 unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, info_off);
unit_idx = unit_num > 0 ? unit_num-1 : 0;
}
// rjf: record this type in the dependency chain count
@@ -2009,7 +2056,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
case DW_TagKind_VolatileType:
case DW_TagKind_ConstType:
case DW_TagKind_ArrayType:
case DW_TagKind_SubrangeType:
case DW_TagKind_Typedef:
case DW_TagKind_SubProgram:
case DW_TagKind_SubroutineType:
@@ -2022,7 +2068,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
U64 direct_type_unit_idx = unit_idx;
if(!contains_1u64(unit_info_tag_range, direct_type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, direct_type_info_off);
if(0 < new_unit_num && new_unit_num <= unit_count)
{
@@ -2055,7 +2100,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
U64 direct_type_unit_idx = unit_idx;
if(!contains_1u64(unit_info_tag_range, direct_type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, direct_type_info_off);
if(0 < new_unit_num && new_unit_num <= unit_count)
{
@@ -2109,17 +2153,21 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
}
// rjf: spawn task
TypeChainTask *new_task = free_task;
if(new_task != 0)
if(direct_type_hash != 0)
{
SLLStackPop(free_task);
TypeChainTask *new_task = free_task;
if(new_task != 0)
{
SLLStackPop(free_task);
}
else
{
new_task = push_array(scratch.arena, TypeChainTask, 1);
}
new_task->next = t->next;
new_task->hash = direct_type_hash;
t->next = new_task;
}
else
{
new_task = push_array(scratch.arena, TypeChainTask, 1);
}
new_task->hash = direct_type_hash;
t->next = new_task;
}
scratch_end(scratch2);
@@ -2201,8 +2249,9 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
// rjf: idx -> type tag node
D2R2_UniqueTypeTagNode *type_tag_node = type_tag_nodes[type_idx];
U64 unit_idx = type_tag_node->unit_idx;
U64 info_off = type_tag_node->info_off;
U64 unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, info_off);
U64 unit_idx = unit_num > 0 ? unit_num-1 : 0;
// rjf: unpack unit
Rng1U64 unit_info_tag_range = unit_info_tag_ranges[unit_idx];
@@ -2254,7 +2303,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
U64 direct_type_unit_idx = unit_idx;
if(!contains_1u64(unit_info_tag_range, direct_type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, direct_type_info_off);
direct_type_unit_idx = (new_unit_num > 0 ? new_unit_num-1 : unit_idx);
}
@@ -2359,7 +2407,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
SLLQueuePush(first_param, last_param, n);
if(!contains_1u64(unit_info_tag_range, n->type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, n->type_info_off);
n->type_unit_idx = (new_unit_num > 0 ? new_unit_num-1 : unit_idx);
}
@@ -2718,8 +2765,9 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
// rjf: idx -> type tag node
D2R2_UniqueTypeTagNode *type_tag_node = type_tag_nodes[type_idx];
U64 unit_idx = type_tag_node->unit_idx;
U64 info_off = type_tag_node->info_off;
U64 unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, info_off);
U64 unit_idx = unit_num > 0 ? unit_num-1 : 0;
// rjf: unpack unit
Rng1U64 unit_info_tag_range = unit_info_tag_ranges[unit_idx];
@@ -2775,7 +2823,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
U64 type_unit_idx = unit_idx;
if(!contains_1u64(unit_info_tag_range, type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, type_info_off);
type_unit_idx = (new_unit_num > 0 ? new_unit_num-1 : unit_idx);
}
@@ -3026,6 +3073,7 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
dst_unit->voff_ranges = unit_voff_ranges;
}
}
lane_sync();
}
////////////////////////////
@@ -3188,7 +3236,6 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
type_unit_idx = unit_idx;
if(!contains_1u64(unit_info_tag_range, type_info_off))
{
Rng1U64Array unit_info_tag_ranges_array = {unit_info_tag_ranges, unit_count};
U64 new_unit_num = rng1u64_array_num_from_value__binary_search(&unit_info_tag_ranges_array, type_info_off);
type_unit_idx = (new_unit_num > 0 ? new_unit_num-1 : unit_idx);
}
@@ -4179,6 +4226,7 @@ d2r2_convert(Arena *arena, D2R2_ConvertParams *params)
}
#undef d2r2_type_from_builtin_kind
lane_sync();
scratch_end(scratch);
return result;
}
src/rdi_from_dwarf/rdi_from_dwarf_2.h
-1
View File
@@ -12,7 +12,6 @@ struct D2R2_UniqueTypeTagNode
{
D2R2_UniqueTypeTagNode *next;
U64 hash;
U64 unit_idx;
U64 info_off;
U64 order_idx;
};