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add comments to point at where strict aliasing rule violations occur in data scripts

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this is definitely not all of them, a thorough rewrite must take place
to fix as many as we can.
This commit is contained in:
Quinn
2025-09-03 22:39:15 +02:00
parent 55635d44ae
commit b72b8eaee1
2 changed files with 13 additions and 9 deletions
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12
src/dat/mcx.c
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@@ -18,8 +18,8 @@
/* Moves chunks `src_s` to `src_e` (inclusive) from `src`, back onto `dst`. */
static void mvchunks(u8 *restrict buf, u8 *src, u8 *dst, int src_s, int src_e) {
assert(src > dst);
u32 *table = (u32 *)buf;
size_t len = src - dst; // acquire the amount of bytes that we shall move
u32 *table = (u32 *)buf; // BUG: strict aliasing
size_t len = src - dst; // acquire the amount of bytes that we shall move
assert(!(len % SECTOR));
// count how many bytes we need to move, whilst updating location data
@@ -36,7 +36,7 @@ static void mvchunks(u8 *restrict buf, u8 *src, u8 *dst, int src_s, int src_e) {
* Returns the bytes removed by this function. */
static size_t delchunk(u8 *restrict buf, size_t rmb, int sidx, int eidx) {
// load the table data
u32 *table = (u32 *)buf;
u32 *table = (u32 *)buf; // BUG: strict aliasing
size_t slen, bidx, blen;
slen = be32toh(table[sidx]) & 0xFF; // acquire the sector length of the chunk
bidx = (be32toh(table[sidx]) >> 8) * SECTOR; // acquire and compute the byte offset the chunk starts at
@@ -62,7 +62,7 @@ size_t mcx_delchunk(u8 *restrict buf, int chunk) {
size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) {
assert(start < end && end < CHUNKS);
u32 *table = (u32 *)buf;
u32 *table = (u32 *)buf; // BUG: strict aliasing
u8 *dst = buf + (be32toh(table[start]) >> 8) * SECTOR;
u8 *src = buf + (be32toh(table[end]) >> 8) * SECTOR;
src += (be32toh(table[end]) & 0xFF) * SECTOR;
@@ -70,8 +70,8 @@ size_t mcx_delchunk_range(u8 *restrict buf, int start, int end) {
// zeroes-out the chunk data within this range. (and set the timestamp)
u32 ts = htobe32(time(NULL));
for (int i = start; i <= end; i++) {
table[i] = 0;
table[i + CHUNKS] = ts;
table[i] = 0; // BUG: strict aliasing
table[i + CHUNKS] = ts; // BUG: strict aliasing
}
// move the remaining chunks down

10
src/dat/nbt.c
View File

@@ -30,6 +30,7 @@ static const u8 *procarr(const u8 *restrict buf, i32 nmem, uint size, struct nbt
if (size == 1) return buf;
size_t i = 0;
while (i < len) {
// BUG: strict aliasing
switch (size) {
case 2: *(u16 *)((*out)->dat + i) = be16toh(*(u16 *)((*out)->dat + i)); break;
case 4: *(u32 *)((*out)->dat + i) = be32toh(*(u32 *)((*out)->dat + i)); break;
@@ -59,7 +60,7 @@ static const u8 *proclist(const u8 *restrict buf, struct nbt_array *restrict *re
}
buf++;
i32 len = (i32)be32toh(*(u32 *)buf);
i32 len = (i32)be32toh(*(u32 *)buf); // BUG: strict aliasing
buf += 4;
return procarr(buf, len, size, out);
}
@@ -71,6 +72,7 @@ const u8 *nbt_proctag(const u8 *restrict buf, u16 slen, void *restrict out) {
i32 nmem;
uint size;
// BUG: strict aliasing
switch (*buf) {
case NBT_I8: *(u8 *)out = *ptr; return ptr + 1;
case NBT_I16: *(u16 *)out = be16toh(*(u16 *)ptr); return ptr + 2;
@@ -102,6 +104,7 @@ const u8 *nbt_proctag(const u8 *restrict buf, u16 slen, void *restrict out) {
static const u8 *nexttag_list(const u8 *restrict ptr, uint *restrict const dpt, i32 *restrict const lens, u8 *restrict const tags) {
const u8 *tag = ptr;
ptr++;
// BUG: strict aliasing
switch (*tag) {
case NBT_END: break;
case NBT_I8: ptr += (i32)be32toh(*(u32 *)ptr) * 1; break;
@@ -114,7 +117,7 @@ static const u8 *nexttag_list(const u8 *restrict ptr, uint *restrict const dpt,
// TODO: handle out of bounds... Might not be required if we use flexible array member
(*dpt)++;
tags[*dpt] = *tag;
lens[*dpt] = (i32)be32toh(*(u32 *)ptr);
lens[*dpt] = (i32)be32toh(*(u32 *)ptr); // BUG: strict aliasing
break;
}
ptr += 4;
@@ -136,9 +139,10 @@ static const u8 *nexttag(const u8 *restrict tag, uint *restrict const dpt, i32 *
*dpt -= !lens[*dpt];
} else {
type = *tag;
ptr += be16toh(*(u16 *)(tag + 1)) + 3;
ptr += be16toh(*(u16 *)(tag + 1)) + 3; // BUG: strict aliasing
}
// BUG: strict aliasing
switch (type) {
case NBT_I8: ptr += 1; break;
case NBT_I16: ptr += 2; break;