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fix relocation failures for smaller instructions

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This commit is contained in:
Pascal Zittlau
2025-12-02 17:45:20 +01:00
parent 4bb03e8312
commit 2d19460095
1 changed files with 41 additions and 18 deletions
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55
src/Patcher.zig
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@@ -485,9 +485,9 @@ fn applyPatch(
@memcpy(flicken_addr, flicken.bytes);
if (request.flicken == .nop) {
const instr_bytes = request.bytes[0..request.size];
const instr = dis.disassembleInstruction(instr_bytes);
const instr = dis.disassembleInstruction(instr_bytes).?;
try relocateInstruction(
instr.?,
instr,
@intCast(allocated_range.start),
flicken_slice[0..request.size],
);
@@ -676,10 +676,8 @@ fn relocateInstruction(
) !void {
const instr = instruction.instruction;
// Iterate all operands
var i: u8 = 0;
while (i < instr.operand_count) : (i += 1) {
for (0..instr.operand_count) |i| {
const operand = &instruction.operands[i];
var result_address: u64 = 0;
// Check for RIP-relative memory operand
const is_rip_rel = operand.type == zydis.ZYDIS_OPERAND_TYPE_MEMORY and
@@ -690,34 +688,34 @@ fn relocateInstruction(
if (!is_rip_rel and !is_rel_imm) continue;
// We have to apply a relocation
var result_address: u64 = 0;
const status = zydis.ZydisCalcAbsoluteAddress(
instr,
operand,
instruction.address,
&result_address,
);
assert(zydis.ZYAN_SUCCESS(status)); // TODO: maybe return an error insteadt
assert(zydis.ZYAN_SUCCESS(status)); // TODO: maybe return an error instead
const new_disp: i32 = blk: {
// Calculate new displacement relative to the new address
// The instruction length remains the same.
const next_rip: i64 = @intCast(address + instr.length);
const new_disp = @as(i64, @intCast(result_address)) - next_rip;
if (new_disp > math.maxInt(i32) or new_disp < math.minInt(i32)) {
return error.RelocationOverflow;
}
break :blk @intCast(new_disp);
};
var offset: u16 = 0;
var size_bits: u8 = 0;
if (is_rip_rel) {
offset = instr.raw.disp.offset;
size_bits = instr.raw.disp.size;
} else {
assert(is_rel_imm);
// For relative immediate, find the matching raw immediate. This loop works because
// x86-64 instructions can have at most one *relative* immediate (branch target).
// For relative immediate, find the matching raw immediate.
var found = false;
for (&instr.raw.imm) |*imm| {
if (imm.is_relative == zydis.ZYAN_TRUE) {
offset = imm.offset;
size_bits = imm.size;
found = true;
break;
}
@@ -726,7 +724,32 @@ fn relocateInstruction(
}
assert(offset != 0);
assert(offset + 4 <= buffer.len);
mem.writeInt(i32, buffer[offset..][0..4], new_disp, .little);
assert(size_bits != 0);
const size_bytes = size_bits / 8;
if (offset + size_bytes > buffer.len) {
return error.RelocationFail;
}
const fits = switch (size_bits) {
8 => new_disp >= math.minInt(i8) and new_disp <= math.maxInt(i8),
16 => new_disp >= math.minInt(i16) and new_disp <= math.maxInt(i16),
32 => new_disp >= math.minInt(i32) and new_disp <= math.maxInt(i32),
64 => true,
else => unreachable,
};
if (!fits) {
return error.RelocationOverflow;
}
const ptr = buffer[offset..];
switch (size_bits) {
8 => ptr[0] = @as(u8, @bitCast(@as(i8, @intCast(new_disp)))),
16 => mem.writeInt(u16, ptr[0..2], @bitCast(@as(i16, @intCast(new_disp))), .little),
32 => mem.writeInt(u32, ptr[0..4], @bitCast(@as(i32, @intCast(new_disp))), .little),
64 => mem.writeInt(u64, ptr[0..8], @bitCast(@as(i64, @intCast(new_disp))), .little),
else => unreachable,
}
}
}