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Wasm: Make sure string constants are placed at a properly aligned offset

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This commit is contained in:
Brian Carroll 2022-01-07 11:26:38 +00:00
parent b8f51fb1bb
commit 265171ad17
1 changed files with 10 additions and 5 deletions
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15
compiler/gen_wasm/src/backend.rs
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@ -30,8 +30,9 @@ use crate::wasm_module::{
LinkingSubSection, LocalId, Signature, SymInfo, ValueType,
};
use crate::{
copy_memory, CopyMemoryConfig, Env, BUILTINS_IMPORT_MODULE_NAME, DEBUG_LOG_SETTINGS,
MEMORY_NAME, PTR_SIZE, PTR_TYPE, STACK_POINTER_GLOBAL_ID, STACK_POINTER_NAME,
copy_memory, round_up_to_alignment, CopyMemoryConfig, Env, BUILTINS_IMPORT_MODULE_NAME,
DEBUG_LOG_SETTINGS, MEMORY_NAME, PTR_SIZE, PTR_TYPE, STACK_POINTER_GLOBAL_ID,
STACK_POINTER_NAME,
};
/// The memory address where the constants data will be loaded during module instantiation.
@ -1465,11 +1466,15 @@ impl<'a> WasmBackend<'a> {
None => {
let const_segment_bytes = &mut self.module.data.segments[CONST_SEGMENT_INDEX].init;
// Store the string in the data section
// Prefix it with a special refcount value (treated as "infinity")
// The string's `elements` field points at the data after the refcount
// Pad the existing data segment to make sure the refcount and string are aligned
let aligned_len = round_up_to_alignment!(const_segment_bytes.len(), 4usize);
const_segment_bytes.resize(aligned_len, 0);
// Prefix the string with "infinite" refcount
let refcount_max_bytes: [u8; 4] = (REFCOUNT_MAX as i32).to_le_bytes();
const_segment_bytes.extend_from_slice(&refcount_max_bytes);
// Add the string bytes to the data segment
let elements_offset = const_segment_bytes.len() as u32;
let elements_addr = elements_offset + CONST_SEGMENT_BASE_ADDR;
const_segment_bytes.extend_from_slice(string.as_bytes());