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Avoid UB.

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Nuno Cruces
2025-06-25 15:02:53 +01:00
parent cd6ba43e77
commit 784f82f42f
3 changed files with 449 additions and 414 deletions
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sqlite3/libc/libc.wasm
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sqlite3/libc/libc.wat
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43
sqlite3/libc/string.h
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@@ -17,7 +17,6 @@ extern "C" {
// Use the builtins if compiled with bulk memory operations.
// Clang will intrinsify using SIMD for small, constant N.
// For everything else, this helps inlining.
__attribute__((weak, always_inline))
void *memset(void *dest, int c, size_t n) {
@@ -80,7 +79,7 @@ int memcmp(const void *vl, const void *vr, size_t n) {
return 0;
}
__attribute__((weak, noinline))
__attribute__((weak))
void *memchr(const void *s, int c, size_t n) {
// When n is zero, a function that locates a character finds no occurrence.
// Otherwise, decrement n to ensure sub_overflow overflows
@@ -92,9 +91,10 @@ void *memchr(const void *s, int c, size_t n) {
// memchr must behave as if it reads characters sequentially
// and stops as soon as a match is found.
// Aligning ensures loads beyond the first match are safe.
// Volatile avoids compiler tricks around out of bounds loads.
// Casting through uintptr_t makes this implementation-defined,
// rather than undefined behavior.
uintptr_t align = (uintptr_t)s % sizeof(v128_t);
const volatile v128_t *v = (v128_t *)((char *)s - align);
const v128_t *v = (v128_t *)((uintptr_t)s - align);
const v128_t vc = wasm_i8x16_splat(c);
for (;;) {
@@ -126,7 +126,7 @@ void *memchr(const void *s, int c, size_t n) {
}
}
__attribute__((weak, noinline))
__attribute__((weak))
void *memrchr(const void *s, int c, size_t n) {
// memrchr is allowed to read up to n bytes from the object.
// Search backward for the last matching character.
@@ -150,18 +150,19 @@ void *memrchr(const void *s, int c, size_t n) {
return NULL;
}
__attribute__((weak, noinline))
__attribute__((weak))
size_t strlen(const char *s) {
// strlen must stop as soon as it finds the terminator.
// Aligning ensures loads beyond the terminator are safe.
// Casting through uintptr_t makes this implementation-defined,
// rather than undefined behavior.
uintptr_t align = (uintptr_t)s % sizeof(v128_t);
const volatile v128_t *v = (v128_t *)(s - align);
const v128_t *v = (v128_t *)((uintptr_t)s - align);
for (;;) {
const v128_t vv = *v;
// Bitmask is slow on AArch64, all_true is much faster.
if (!wasm_i8x16_all_true(vv)) {
const v128_t cmp = wasm_i8x16_eq(vv, (v128_t){});
if (!wasm_i8x16_all_true(*v)) {
const v128_t cmp = wasm_i8x16_eq(*v, (v128_t){});
// Clear the bits corresponding to alignment (little-endian)
// so we can count trailing zeros.
int mask = wasm_i8x16_bitmask(cmp) >> align << align;
@@ -183,14 +184,14 @@ size_t strlen(const char *s) {
static char *__strchrnul(const char *s, int c) {
// strchrnul must stop as soon as it finds the terminator.
// Aligning ensures loads beyond the terminator are safe.
// Volatile avoids compiler tricks around out of bounds loads.
// Casting through uintptr_t makes this implementation-defined,
// rather than undefined behavior.
uintptr_t align = (uintptr_t)s % sizeof(v128_t);
const volatile v128_t *v = (v128_t *)(s - align);
const v128_t *v = (v128_t *)((uintptr_t)s - align);
const v128_t vc = wasm_i8x16_splat(c);
for (;;) {
const v128_t vv = *v;
const v128_t cmp = wasm_i8x16_eq(vv, (v128_t){}) | wasm_i8x16_eq(vv, vc);
const v128_t cmp = wasm_i8x16_eq(*v, (v128_t){}) | wasm_i8x16_eq(*v, vc);
// Bitmask is slow on AArch64, any_true is much faster.
if (wasm_v128_any_true(cmp)) {
// Clear the bits corresponding to alignment (little-endian)
@@ -284,13 +285,14 @@ static v128_t __wasm_v128_chkbits(__wasm_v128_bitmap256_t bitmap, v128_t v) {
#undef wasm_i8x16_relaxed_swizzle
__attribute__((weak, noinline))
__attribute__((weak))
size_t strspn(const char *s, const char *c) {
// strspn must stop as soon as it finds the terminator.
// Aligning ensures loads beyond the terminator are safe.
// Volatile avoids compiler tricks around out of bounds loads.
// Casting through uintptr_t makes this implementation-defined,
// rather than undefined behavior.
uintptr_t align = (uintptr_t)s % sizeof(v128_t);
const volatile v128_t *v = (v128_t *)(s - align);
const v128_t *v = (v128_t *)((uintptr_t)s - align);
if (!c[0]) return 0;
if (!c[1]) {
@@ -346,15 +348,16 @@ size_t strspn(const char *s, const char *c) {
}
}
__attribute__((weak, noinline))
__attribute__((weak))
size_t strcspn(const char *s, const char *c) {
if (!c[0] || !c[1]) return __strchrnul(s, *c) - s;
// strcspn must stop as soon as it finds the terminator.
// Aligning ensures loads beyond the terminator are safe.
// Volatile avoids compiler tricks around out of bounds loads.
// Casting through uintptr_t makes this implementation-defined,
// rather than undefined behavior.
uintptr_t align = (uintptr_t)s % sizeof(v128_t);
const volatile v128_t *v = (v128_t *)(s - align);
const v128_t *v = (v128_t *)((uintptr_t)s - align);
__wasm_v128_bitmap256_t bitmap = {};