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fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

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Merged
Jarred-Sumner merged 2 commits into from
Dec 7, 2025
+37 −32
Merged

fix(compile): use 8-byte header for embedded section to ensure bytecode alignment #25377

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457ab88
fix(compile): use 8-byte header for embedded section to ensure byteco…
dylan-conway Dec 6, 2025
9e578ff
fix(test): update PE test to use 8-byte size header
dylan-conway Dec 6, 2025
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8 changes: 5 additions & 3 deletions src/StandaloneModuleGraph.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -119,24 +119,26 @@ pub const StandaloneModuleGraph = struct {
};

const Macho = struct {
pub extern "C" fn Bun__getStandaloneModuleGraphMachoLength() ?*align(1) u32;
pub extern "C" fn Bun__getStandaloneModuleGraphMachoLength() ?*align(1) u64;

pub fn getData() ?[]const u8 {
if (Bun__getStandaloneModuleGraphMachoLength()) |length| {
if (length.* < 8) {
return null;
}

// BlobHeader has 8 bytes size (u64), so data starts at offset 8.
const data_offset = @sizeOf(u64);
const slice_ptr: [*]const u8 = @ptrCast(length);
return slice_ptr[4..][0..length.*];
return slice_ptr[data_offset..][0..length.*];
}

return null;
}
};

const PE = struct {
pub extern "C" fn Bun__getStandaloneModuleGraphPELength() u32;
pub extern "C" fn Bun__getStandaloneModuleGraphPELength() u64;
pub extern "C" fn Bun__getStandaloneModuleGraphPEData() ?[*]u8;

pub fn getData() ?[]const u8 {
Expand Down
13 changes: 7 additions & 6 deletions src/bun.js/bindings/c-bindings.cpp
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Expand Up @@ -910,14 +910,14 @@ extern "C" void Bun__signpost_emit(os_log_t log, os_signpost_type_t type, os_sig

extern "C" {
struct BlobHeader {
uint32_t size;
uint64_t size; // 64-bit to ensure data[] starts at 8-byte aligned offset (required for bytecode cache)
uint8_t data[];
} __attribute__((aligned(BLOB_HEADER_ALIGNMENT)));
}

extern "C" BlobHeader __attribute__((section("__BUN,__bun"))) BUN_COMPILED = { 0, 0 };

extern "C" uint32_t* Bun__getStandaloneModuleGraphMachoLength()
extern "C" uint64_t* Bun__getStandaloneModuleGraphMachoLength()
{
return &BUN_COMPILED.size;
}
Expand All @@ -927,7 +927,7 @@ extern "C" uint32_t* Bun__getStandaloneModuleGraphMachoLength()
#include <windows.h>
#include <winnt.h>

static uint32_t* pe_section_size = nullptr;
static uint64_t* pe_section_size = nullptr;
static uint8_t* pe_section_data = nullptr;

// Helper function to find and map the .bun section
Expand All @@ -949,9 +949,10 @@ static bool initializePESection()
for (int i = 0; i < ntHeaders->FileHeader.NumberOfSections; i++) {
if (strncmp((char*)sectionHeader->Name, ".bun", 4) == 0) {
// Found the .bun section
// Section format: 8 bytes size (uint64_t) + data
BYTE* sectionData = (BYTE*)hModule + sectionHeader->VirtualAddress;
pe_section_size = (uint32_t*)sectionData;
pe_section_data = sectionData + sizeof(uint32_t);
pe_section_size = (uint64_t*)sectionData;
pe_section_data = sectionData + sizeof(uint64_t); // Skip size (8)
return true;
}
sectionHeader++;
Expand All @@ -960,7 +961,7 @@ static bool initializePESection()
return false;
}

extern "C" uint32_t Bun__getStandaloneModuleGraphPELength()
extern "C" uint64_t Bun__getStandaloneModuleGraphPELength()
{
if (!initializePESection()) return 0;
return pe_section_size ? *pe_section_size : 0;
Expand Down
10 changes: 5 additions & 5 deletions src/macho.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ pub const MachoFile = struct {
const PAGE_SIZE: u64 = 1 << 12;
const HASH_SIZE: usize = 32; // SHA256 = 32 bytes

const header_size = @sizeOf(u32);
const header_size = @sizeOf(u64);
const total_size = header_size + data.len;
const aligned_size = alignSize(total_size, blob_alignment);

Expand Down Expand Up @@ -164,14 +164,14 @@ pub const MachoFile = struct {
const prev_after_bun_slice = prev_data_slice[original_segsize..];
bun.memmove(after_bun_slice, prev_after_bun_slice);

// Now we copy the u32 size header
std.mem.writeInt(u32, self.data.items[original_fileoff..][0..4], @intCast(data.len), .little);
// Now we copy the u64 size header (8 bytes for alignment)
std.mem.writeInt(u64, self.data.items[original_fileoff..][0..8], @intCast(data.len), .little);

// Now we copy the data itself
@memcpy(self.data.items[original_fileoff + 4 ..][0..data.len], data);
@memcpy(self.data.items[original_fileoff + 8 ..][0..data.len], data);

// Lastly, we zero any of the padding that was added
const padding_bytes = self.data.items[original_fileoff..][data.len + 4 .. aligned_size];
const padding_bytes = self.data.items[original_fileoff..][data.len + 8 .. aligned_size];
@memset(padding_bytes, 0);

if (code_sign_cmd) |cs| {
Expand Down
30 changes: 16 additions & 14 deletions src/pe.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -500,11 +500,11 @@ pub const PEFile = struct {
}
}

// Check for overflow before adding 4
if (data_to_embed.len > std.math.maxInt(u32) - 4) {
// Check for overflow before adding 8
if (data_to_embed.len > std.math.maxInt(u32) - 8) {
return error.Overflow;
}
const payload_len = @as(u32, @intCast(data_to_embed.len + 4)); // 4 for LE length prefix
const payload_len = @as(u32, @intCast(data_to_embed.len + 8)); // 8 for LE length prefix
const raw_size = try alignUpU32(payload_len, opt.file_alignment);
const new_va = try alignUpU32(last_va_end, opt.section_alignment);
const new_raw = try alignUpU32(last_file_end, opt.file_alignment);
Expand Down Expand Up @@ -536,9 +536,9 @@ pub const PEFile = struct {
std.mem.copyForwards(u8, self.data.items[new_sh_off .. new_sh_off + @sizeOf(SectionHeader)], std.mem.asBytes(&sh));

// 8. Write payload
// At data[new_raw ..]: write LE length prefix then data
std.mem.writeInt(u32, self.data.items[new_raw..][0..4], @intCast(data_to_embed.len), .little);
@memcpy(self.data.items[new_raw + 4 ..][0..data_to_embed.len], data_to_embed);
// At data[new_raw ..]: write u64 LE length prefix, then data
std.mem.writeInt(u64, self.data.items[new_raw..][0..8], @intCast(data_to_embed.len), .little);
@memcpy(self.data.items[new_raw + 8 ..][0..data_to_embed.len], data_to_embed);

// 9. Update headers
// Get fresh pointers after resize
Expand Down Expand Up @@ -573,7 +573,8 @@ pub const PEFile = struct {
const section_headers = try self.getSectionHeaders();
for (section_headers) |section| {
if (std.mem.eql(u8, section.name[0..8], &BUN_SECTION_NAME)) {
if (section.size_of_raw_data < @sizeOf(u32)) {
// Header: 8 bytes size (u64)
if (section.size_of_raw_data < @sizeOf(u64)) {
return error.InvalidBunSection;
}

Expand All @@ -585,36 +586,37 @@ pub const PEFile = struct {
}

const section_data = self.data.items[section.pointer_to_raw_data..][0..section.size_of_raw_data];
const data_size = std.mem.readInt(u32, section_data[0..4], .little);
const data_size = std.mem.readInt(u64, section_data[0..8], .little);

if (data_size + @sizeOf(u32) > section.size_of_raw_data) {
if (data_size + @sizeOf(u64) > section.size_of_raw_data) {
return error.InvalidBunSection;
}

return section_data[4..][0..data_size];
// Data starts at offset 8 (after u64 size)
return section_data[8..][0..data_size];
}
}
return error.BunSectionNotFound;
}

/// Get the length of the Bun section data
pub fn getBunSectionLength(self: *const PEFile) !u32 {
pub fn getBunSectionLength(self: *const PEFile) !u64 {
const section_headers = try self.getSectionHeaders();
for (section_headers) |section| {
if (std.mem.eql(u8, section.name[0..8], &BUN_SECTION_NAME)) {
if (section.size_of_raw_data < @sizeOf(u32)) {
if (section.size_of_raw_data < @sizeOf(u64)) {
return error.InvalidBunSection;
}

// Bounds check
if (section.pointer_to_raw_data >= self.data.items.len or
section.pointer_to_raw_data + @sizeOf(u32) > self.data.items.len)
section.pointer_to_raw_data + @sizeOf(u64) > self.data.items.len)
{
return error.InvalidBunSection;
}

const section_data = self.data.items[section.pointer_to_raw_data..];
return std.mem.readInt(u32, section_data[0..4], .little);
return std.mem.readInt(u64, section_data[0..8], .little);
}
}
return error.BunSectionNotFound;
Expand Down
8 changes: 4 additions & 4 deletions test/regression/issue/pe-codesigning-integrity.test.ts
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Expand Up @@ -119,8 +119,8 @@ describe.if(isWindows)("PE codesigning integrity", () => {
// Read the .bun section data
const sectionData = new Uint8Array(this.buffer, bunSection.pointerToRawData, bunSection.sizeOfRawData);

// First 4 bytes should be the data size
const dataSize = new DataView(sectionData.buffer, bunSection.pointerToRawData).getUint32(0, true);
// First 8 bytes should be the data size (u64 for 8-byte alignment)
const dataSize = Number(new DataView(sectionData.buffer, bunSection.pointerToRawData).getBigUint64(0, true));

// Validate the size is reasonable - it should match or be close to virtual size
if (dataSize > bunSection.sizeOfRawData || dataSize === 0) {
Expand All @@ -133,8 +133,8 @@ describe.if(isWindows)("PE codesigning integrity", () => {
throw new Error(`Invalid .bun section: data size ${dataSize} exceeds virtual size ${bunSection.virtualSize}`);
}

// Extract the actual embedded data (skip the 4-byte size header)
const embeddedData = sectionData.slice(4, 4 + dataSize);
// Extract the actual embedded data (skip the 8-byte size header)
const embeddedData = sectionData.slice(8, 8 + dataSize);

return {
section: bunSection,
Expand Down