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allow greedy allocation for faster patching

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Pascal Zittlau
2025-12-08 15:03:44 +01:00
parent 49ae70ec2c
commit 0788dd30f2
1 changed files with 18 additions and 6 deletions
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24
src/Patcher.zig
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@@ -351,7 +351,7 @@ fn attemptDirectOrPunning(
// mapped. While harmless (it becomes an unused executable page), it is technically a // mapped. While harmless (it becomes an unused executable page), it is technically a
// memory leak. A future fix should track "current attempt" pages separately and unmap // memory leak. A future fix should track "current attempt" pages separately and unmap
// them on failure. // them on failure.
while (pii.next(&patcher.address_allocator)) |allocated_range| { while (pii.next(&patcher.address_allocator, .exhaustive)) |allocated_range| {
try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(allocated_range)); try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(allocated_range));
patcher.ensureRangeWritable( patcher.ensureRangeWritable(
allocated_range, allocated_range,
@@ -426,7 +426,7 @@ fn attemptSuccessorEviction(
succ_request.size, succ_request.size,
succ_flicken.size(), succ_flicken.size(),
); );
while (succ_pii.next(&patcher.address_allocator)) |succ_range| { while (succ_pii.next(&patcher.address_allocator, .greedy)) |succ_range| {
// Ensure bytes match original before retry. // Ensure bytes match original before retry.
assert(mem.eql( assert(mem.eql(
u8, u8,
@@ -464,7 +464,7 @@ fn attemptSuccessorEviction(
request.size, request.size,
flicken.size(), flicken.size(),
); );
while (orig_pii.next(&patcher.address_allocator)) |orig_range| { while (orig_pii.next(&patcher.address_allocator, .greedy)) |orig_range| {
if (succ_range.touches(orig_range)) continue; if (succ_range.touches(orig_range)) continue;
try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(orig_range)); try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(orig_range));
patcher.ensureRangeWritable( patcher.ensureRangeWritable(
@@ -566,7 +566,7 @@ fn attemptNeighborEviction(
patch_flicken.size(), patch_flicken.size(),
); );
while (patch_pii.next(&patcher.address_allocator)) |patch_range| { while (patch_pii.next(&patcher.address_allocator, .greedy)) |patch_range| {
// J_Patch MUST NOT use prefixes, because it's punned inside J_Victim. // J_Patch MUST NOT use prefixes, because it's punned inside J_Victim.
// Adding prefixes would shift J_Patch relative to J_Victim, making constraints harder. // Adding prefixes would shift J_Patch relative to J_Victim, making constraints harder.
if (patch_pii.num_prefixes > 0) break; if (patch_pii.num_prefixes > 0) break;
@@ -602,7 +602,7 @@ fn attemptNeighborEviction(
victim_flicken.size(), victim_flicken.size(),
); );
while (victim_pii.next(&patcher.address_allocator)) |victim_range| { while (victim_pii.next(&patcher.address_allocator, .greedy)) |victim_range| {
if (patch_range.touches(victim_range)) continue; if (patch_range.touches(victim_range)) continue;
try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(victim_range)); try pages_made_writable.ensureUnusedCapacity(arena, touchedPageCount(victim_range));
@@ -874,9 +874,18 @@ const PatchInstructionIterator = struct {
}; };
} }
pub const Strategy = enum {
/// Iterates through all possible ranges.
/// Useful for finding the optimal allocation (fewest prefixes).
exhaustive,
/// Try one allocation per found valid_range. Dramatically faster.
greedy,
};
fn next( fn next(
pii: *PatchInstructionIterator, pii: *PatchInstructionIterator,
address_allocator: *AddressAllocator, address_allocator: *AddressAllocator,
strategy: Strategy,
) ?Range { ) ?Range {
const State = enum { const State = enum {
allocation, allocation,
@@ -892,7 +901,10 @@ const PatchInstructionIterator = struct {
assert(allocated_range.size() == pii.flicken_size); assert(allocated_range.size() == pii.flicken_size);
// Advancing the valid range, such that the next call to `findAllocation` won't // Advancing the valid range, such that the next call to `findAllocation` won't
// find the same range again. // find the same range again.
pii.valid_range.start = allocated_range.start + 1; switch (strategy) {
.exhaustive => pii.valid_range.start = allocated_range.start + 1,
.greedy => pii.valid_range.start = pii.valid_range.end,
}
return allocated_range; return allocated_range;
} else { } else {
continue :blk .range; continue :blk .range;