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8264908: Investigate adding BOT range check in G1BlockOffsetTablePart::block_at_or_preceding #4775

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8264908: Investigate adding BOT range check in G1BlockOffsetTablePart::block_at_or_preceding #4775

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refactor G1BlockOffsetTablePart::block_at_or_preceding to add assert …
walulyai Jul 14, 2021
1d71c8c
@albertnetymk suggested changes
walulyai Jul 14, 2021
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5 changes: 2 additions & 3 deletions src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp
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Original file line number Diff line number Diff line change
@@ -115,9 +115,8 @@ inline HeapWord* G1BlockOffsetTablePart::block_at_or_preceding(const void* addr)
"Object crossed region boundary, found offset %u instead of 0",
(uint) _bot->offset_array(_bot->index_for(_hr->bottom())));
size_t index = _bot->index_for(addr);
// We must make sure that the offset table entry we use is valid. If
// "addr" is past the end, start at the last valid index.
index = MIN2(index, _next_offset_index - 1);
// We must make sure that the offset table entry we use is valid.
assert(index < _next_offset_index, "Precondition");
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I feel a bit uneasy that the caller (block_start) allows more than the callee (values < _hr->end()), but this is probably the change that is supposed to be coming?
Looks good, but I would have preferred the original change or the upcoming change with some asserts included.

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I can add the deferred change, instead of splitting it off into a separate PR.

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the caller (block_start) allows more than the callee (values < _hr->end())

That path should never be taken, so I am not worried about. I suggested putting that in another PR since those assertions are not obvious from the current ticket title. Anyway, this is subjective.

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@albertnetymk : I know. Still it seems something is missing to me, but that's subjective. Let's just defer it.


HeapWord* q = _bot->address_for_index(index);

55 changes: 0 additions & 55 deletions src/hotspot/share/gc/g1/heapRegion.cpp
View file
Original file line number Diff line number Diff line change
@@ -734,61 +734,6 @@ void HeapRegion::verify(VerifyOption vo,
return;
}

HeapWord* the_end = end();
// Do some extra BOT consistency checking for addresses in the
// range [top, end). BOT look-ups in this range should yield
// top. No point in doing that if top == end (there's nothing there).
if (p < the_end) {
// Look up top
HeapWord* addr_1 = p;
HeapWord* b_start_1 = block_start_const(addr_1);
if (b_start_1 != p) {
log_error(gc, verify)("BOT look up for top: " PTR_FORMAT " "
" yielded " PTR_FORMAT ", expecting " PTR_FORMAT,
p2i(addr_1), p2i(b_start_1), p2i(p));
*failures = true;
return;
}

// Look up top + 1
HeapWord* addr_2 = p + 1;
if (addr_2 < the_end) {
HeapWord* b_start_2 = block_start_const(addr_2);
if (b_start_2 != p) {
log_error(gc, verify)("BOT look up for top + 1: " PTR_FORMAT " "
" yielded " PTR_FORMAT ", expecting " PTR_FORMAT,
p2i(addr_2), p2i(b_start_2), p2i(p));
*failures = true;
return;
}
}

// Look up an address between top and end
size_t diff = pointer_delta(the_end, p) / 2;
HeapWord* addr_3 = p + diff;
if (addr_3 < the_end) {
HeapWord* b_start_3 = block_start_const(addr_3);
if (b_start_3 != p) {
log_error(gc, verify)("BOT look up for top + diff: " PTR_FORMAT " "
" yielded " PTR_FORMAT ", expecting " PTR_FORMAT,
p2i(addr_3), p2i(b_start_3), p2i(p));
*failures = true;
return;
}
}

// Look up end - 1
HeapWord* addr_4 = the_end - 1;
HeapWord* b_start_4 = block_start_const(addr_4);
if (b_start_4 != p) {
log_error(gc, verify)("BOT look up for end - 1: " PTR_FORMAT " "
" yielded " PTR_FORMAT ", expecting " PTR_FORMAT,
p2i(addr_4), p2i(b_start_4), p2i(p));
*failures = true;
return;
}
}

verify_strong_code_roots(vo, failures);
}