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elf: Put constant data in the .rodata section

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Allocate a new program header and a new section to accomodate the read-only data
section ".rodata".

Separate TextBlock into multiple TextBlockList, to separate decl in different
sections.

If a Decl is not a function, it is added to the .rodata section.
This commit is contained in:
Ersikan 2021-03-12 23:46:51 +01:00 committed by Andrew Kelley
parent 44061cd760
commit e15a267668
1 changed files with 106 additions and 40 deletions
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146
src/link/Elf.zig
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@ -54,13 +54,14 @@ phdr_load_re_index: ?u16 = null,
/// The index into the program headers of the global offset table.
/// It needs PT_LOAD and Read flags.
phdr_got_index: ?u16 = null,
/// The index into the program headers of a PT_LOAD program header with Read flag
phdr_load_ro_index: ?u16 = null,
entry_addr: ?u64 = null,
debug_strtab: std.ArrayListUnmanaged(u8) = std.ArrayListUnmanaged(u8){},
shstrtab: std.ArrayListUnmanaged(u8) = std.ArrayListUnmanaged(u8){},
shstrtab_index: ?u16 = null,
text_section_index: ?u16 = null,
symtab_section_index: ?u16 = null,
got_section_index: ?u16 = null,
debug_info_section_index: ?u16 = null,
@ -115,8 +116,8 @@ error_flags: File.ErrorFlags = File.ErrorFlags{},
/// overcapacity can be negative. A simple way to have negative overcapacity is to
/// allocate a fresh text block, which will have ideal capacity, and then grow it
/// by 1 byte. It will then have -1 overcapacity.
text_block_free_list: std.ArrayListUnmanaged(*TextBlock) = .{},
last_text_block: ?*TextBlock = null,
text_block_list: TextBlockList = .{},
rodata_block_list: TextBlockList = .{},
/// A list of `SrcFn` whose Line Number Programs have surplus capacity.
/// This is the same concept as `text_block_free_list`; see those doc comments.
@ -204,6 +205,14 @@ pub const TextBlock = struct {
}
};
/// A list of text blocks in a specific section
const TextBlockList = struct {
free_list: std.ArrayListUnmanaged(*TextBlock) = .{},
last_block: ?*TextBlock = null,
phdr_index: ?u16 = null,
section_index: ?u16 = null,
};
pub const Export = struct {
sym_index: ?u32 = null,
};
@ -314,7 +323,8 @@ pub fn deinit(self: *Elf) void {
self.global_symbol_free_list.deinit(self.base.allocator);
self.local_symbol_free_list.deinit(self.base.allocator);
self.offset_table_free_list.deinit(self.base.allocator);
self.text_block_free_list.deinit(self.base.allocator);
self.text_block_list.free_list.deinit(self.base.allocator);
self.rodata_block_list.free_list.deinit(self.base.allocator);
self.dbg_line_fn_free_list.deinit(self.base.allocator);
self.dbg_info_decl_free_list.deinit(self.base.allocator);
self.offset_table.deinit(self.base.allocator);
@ -450,6 +460,7 @@ pub fn populateMissingMetadata(self: *Elf) !void {
const ptr_size: u8 = self.ptrWidthBytes();
if (self.phdr_load_re_index == null) {
self.phdr_load_re_index = @intCast(u16, self.program_headers.items.len);
self.text_block_list.phdr_index = self.phdr_load_re_index;
const file_size = self.base.options.program_code_size_hint;
const p_align = 0x1000;
const off = self.findFreeSpace(file_size, p_align);
@ -492,6 +503,29 @@ pub fn populateMissingMetadata(self: *Elf) !void {
});
self.phdr_table_dirty = true;
}
if (self.phdr_load_ro_index == null) {
self.phdr_load_ro_index = @intCast(u16, self.program_headers.items.len);
self.rodata_block_list.phdr_index = self.phdr_load_ro_index;
// TODO Find a hint about how much data need to be in rodata ?
const file_size = 1024;
// Same reason as for GOT
const p_align = if (self.base.options.target.os.tag == .linux) 0x1000 else @as(u16, ptr_size);
const off = self.findFreeSpace(file_size, p_align);
log.debug("found PT_LOAD free space 0x{x} to 0x{x}\n", .{ off, off + file_size });
// TODO Same as for GOT
const rodata_addr: u32 = if (self.base.options.target.cpu.arch.ptrBitWidth() >= 32) 0x6000000 else 0xD000;
try self.program_headers.append(self.base.allocator, .{
.p_type = elf.PT_LOAD,
.p_offset = off,
.p_filesz = file_size,
.p_vaddr = rodata_addr,
.p_paddr = rodata_addr,
.p_memsz = file_size,
.p_align = p_align,
.p_flags = elf.PF_R,
});
self.phdr_table_dirty = true;
}
if (self.shstrtab_index == null) {
self.shstrtab_index = @intCast(u16, self.sections.items.len);
assert(self.shstrtab.items.len == 0);
@ -513,8 +547,8 @@ pub fn populateMissingMetadata(self: *Elf) !void {
self.shstrtab_dirty = true;
self.shdr_table_dirty = true;
}
if (self.text_section_index == null) {
self.text_section_index = @intCast(u16, self.sections.items.len);
if (self.text_block_list.section_index == null) {
self.text_block_list.section_index = @intCast(u16, self.sections.items.len);
const phdr = &self.program_headers.items[self.phdr_load_re_index.?];
try self.sections.append(self.base.allocator, .{
@ -549,6 +583,24 @@ pub fn populateMissingMetadata(self: *Elf) !void {
});
self.shdr_table_dirty = true;
}
if (self.rodata_block_list.section_index == null) {
self.rodata_block_list.section_index = @intCast(u16, self.sections.items.len);
const phdr = &self.program_headers.items[self.phdr_load_ro_index.?];
try self.sections.append(self.base.allocator, .{
.sh_name = try self.makeString(".rodata"),
.sh_type = elf.SHT_PROGBITS,
.sh_flags = elf.SHF_ALLOC,
.sh_addr = phdr.p_vaddr,
.sh_offset = phdr.p_offset,
.sh_size = phdr.p_filesz,
.sh_link = 0,
.sh_info = 0,
.sh_addralign = phdr.p_align,
.sh_entsize = 0,
});
self.shdr_table_dirty = true;
}
if (self.symtab_section_index == null) {
self.symtab_section_index = @intCast(u16, self.sections.items.len);
const min_align: u16 = if (small_ptr) @alignOf(elf.Elf32_Sym) else @alignOf(elf.Elf64_Sym);
@ -1927,17 +1979,17 @@ fn writeElfHeader(self: *Elf) !void {
try self.base.file.?.pwriteAll(hdr_buf[0..index], 0);
}
fn freeTextBlock(self: *Elf, text_block: *TextBlock) void {
fn freeTextBlock(self: *Elf, block_list: *TextBlockList, text_block: *TextBlock) void {
var already_have_free_list_node = false;
{
var i: usize = 0;
// TODO turn text_block_free_list into a hash map
while (i < self.text_block_free_list.items.len) {
if (self.text_block_free_list.items[i] == text_block) {
_ = self.text_block_free_list.swapRemove(i);
while (i < block_list.free_list.items.len) {
if (block_list.free_list.items[i] == text_block) {
_ = block_list.free_list.swapRemove(i);
continue;
}
if (self.text_block_free_list.items[i] == text_block.prev) {
if (block_list.free_list.items[i] == text_block.prev) {
already_have_free_list_node = true;
}
i += 1;
@ -1945,9 +1997,9 @@ fn freeTextBlock(self: *Elf, text_block: *TextBlock) void {
}
// TODO process free list for dbg info just like we do above for vaddrs
if (self.last_text_block == text_block) {
if (block_list.last_block == text_block) {
// TODO shrink the .text section size here
self.last_text_block = text_block.prev;
block_list.last_block = text_block.prev;
}
if (self.dbg_info_decl_first == text_block) {
self.dbg_info_decl_first = text_block.dbg_info_next;
@ -1963,7 +2015,7 @@ fn freeTextBlock(self: *Elf, text_block: *TextBlock) void {
if (!already_have_free_list_node and prev.freeListEligible(self.*)) {
// The free list is heuristics, it doesn't have to be perfect, so we can
// ignore the OOM here.
self.text_block_free_list.append(self.base.allocator, prev) catch {};
block_list.free_list.append(self.base.allocator, prev) catch {};
}
} else {
text_block.prev = null;
@ -1990,25 +2042,24 @@ fn freeTextBlock(self: *Elf, text_block: *TextBlock) void {
}
}
fn shrinkTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64) void {
fn shrinkTextBlock(self: *Elf, block_list: *TextBlockList, text_block: *TextBlock, new_block_size: u64) void {
_ = self;
_ = block_list;
_ = text_block;
_ = new_block_size;
// TODO check the new capacity, and if it crosses the size threshold into a big enough
// capacity, insert a free list node for it.
}
fn growTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, alignment: u64) !u64 {
fn growTextBlock(self: *Elf, block_list: *TextBlockList, text_block: *TextBlock, new_block_size: u64, alignment: u64) !u64 {
const sym = self.local_symbols.items[text_block.local_sym_index];
const align_ok = mem.alignBackwardGeneric(u64, sym.st_value, alignment) == sym.st_value;
const need_realloc = !align_ok or new_block_size > text_block.capacity(self.*);
if (!need_realloc) return sym.st_value;
return self.allocateTextBlock(text_block, new_block_size, alignment);
return self.allocateTextBlock(block_list, text_block, new_block_size, alignment);
}
fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, alignment: u64) !u64 {
const phdr = &self.program_headers.items[self.phdr_load_re_index.?];
const shdr = &self.sections.items[self.text_section_index.?];
fn allocateTextBlock(self: *Elf, block_list: *TextBlockList, text_block: *TextBlock, new_block_size: u64, alignment: u64) !u64 {
const phdr = &self.program_headers.items[block_list.phdr_index.?];
const shdr = &self.sections.items[block_list.section_index.?];
const new_block_ideal_capacity = padToIdeal(new_block_size);
// We use these to indicate our intention to update metadata, placing the new block,
@ -2023,8 +2074,8 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
// The list is unordered. We'll just take the first thing that works.
const vaddr = blk: {
var i: usize = 0;
while (i < self.text_block_free_list.items.len) {
const big_block = self.text_block_free_list.items[i];
while (i < block_list.free_list.items.len) {
const big_block = block_list.free_list.items[i];
// We now have a pointer to a live text block that has too much capacity.
// Is it enough that we could fit this new text block?
const sym = self.local_symbols.items[big_block.local_sym_index];
@ -2039,7 +2090,7 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
// should be deleted because the block that it points to has grown to take up
// more of the extra capacity.
if (!big_block.freeListEligible(self.*)) {
_ = self.text_block_free_list.swapRemove(i);
_ = block_list.free_list.swapRemove(i);
} else {
i += 1;
}
@ -2057,7 +2108,7 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
free_list_removal = i;
}
break :blk new_start_vaddr;
} else if (self.last_text_block) |last| {
} else if (block_list.last_block) |last| {
const sym = self.local_symbols.items[last.local_sym_index];
const ideal_capacity = padToIdeal(sym.st_size);
const ideal_capacity_end_vaddr = sym.st_value + ideal_capacity;
@ -2077,7 +2128,7 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
if (needed_size > text_capacity) {
// Must move the entire text section.
const new_offset = self.findFreeSpace(needed_size, 0x1000);
const text_size = if (self.last_text_block) |last| blk: {
const text_size = if (block_list.last_block) |last| blk: {
const sym = self.local_symbols.items[last.local_sym_index];
break :blk (sym.st_value + sym.st_size) - phdr.p_vaddr;
} else 0;
@ -2086,7 +2137,7 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
shdr.sh_offset = new_offset;
phdr.p_offset = new_offset;
}
self.last_text_block = text_block;
block_list.last_block = text_block;
shdr.sh_size = needed_size;
phdr.p_memsz = needed_size;
@ -2124,11 +2175,19 @@ fn allocateTextBlock(self: *Elf, text_block: *TextBlock, new_block_size: u64, al
text_block.next = null;
}
if (free_list_removal) |i| {
_ = self.text_block_free_list.swapRemove(i);
_ = block_list.free_list.swapRemove(i);
}
return vaddr;
}
/// Get the block list corresponding to a specific decl
/// For example, if the decl is a function, it returns the list of the section .text
fn getDeclBlockList(self: *Elf, decl: *const Module.Decl) *TextBlockList {
// const is_fn = decl.val.tag() == .function;
const is_fn = decl.ty.zigTypeTag() == .Fn;
return if (is_fn) &self.text_block_list else &self.rodata_block_list;
}
pub fn allocateDeclIndexes(self: *Elf, decl: *Module.Decl) !void {
if (self.llvm_object) |_| return;
@ -2172,8 +2231,10 @@ pub fn freeDecl(self: *Elf, decl: *Module.Decl) void {
if (self.llvm_object) |llvm_object| return llvm_object.freeDecl(decl);
}
const block_list = self.getDeclBlockList(decl);
// Appending to free lists is allowed to fail because the free lists are heuristics based anyway.
self.freeTextBlock(&decl.link.elf);
self.freeTextBlock(block_list, &decl.link.elf);
if (decl.link.elf.local_sym_index != 0) {
self.local_symbol_free_list.append(self.base.allocator, decl.link.elf.local_sym_index) catch {};
self.offset_table_free_list.append(self.base.allocator, decl.link.elf.offset_table_index) catch {};
@ -2216,6 +2277,8 @@ fn deinitRelocs(gpa: Allocator, table: *File.DbgInfoTypeRelocsTable) void {
fn updateDeclCode(self: *Elf, decl: *Module.Decl, code: []const u8, stt_bits: u8) !*elf.Elf64_Sym {
const required_alignment = decl.ty.abiAlignment(self.base.options.target);
const block_list = self.getDeclBlockList(decl);
assert(decl.link.elf.local_sym_index != 0); // Caller forgot to allocateDeclIndexes()
const local_sym = &self.local_symbols.items[decl.link.elf.local_sym_index];
if (local_sym.st_size != 0) {
@ -2223,7 +2286,7 @@ fn updateDeclCode(self: *Elf, decl: *Module.Decl, code: []const u8, stt_bits: u8
const need_realloc = code.len > capacity or
!mem.isAlignedGeneric(u64, local_sym.st_value, required_alignment);
if (need_realloc) {
const vaddr = try self.growTextBlock(&decl.link.elf, code.len, required_alignment);
const vaddr = try self.growTextBlock(block_list, &decl.link.elf, code.len, required_alignment);
log.debug("growing {s} from 0x{x} to 0x{x}", .{ decl.name, local_sym.st_value, vaddr });
if (vaddr != local_sym.st_value) {
local_sym.st_value = vaddr;
@ -2233,27 +2296,28 @@ fn updateDeclCode(self: *Elf, decl: *Module.Decl, code: []const u8, stt_bits: u8
try self.writeOffsetTableEntry(decl.link.elf.offset_table_index);
}
} else if (code.len < local_sym.st_size) {
self.shrinkTextBlock(&decl.link.elf, code.len);
self.shrinkTextBlock(block_list, &decl.link.elf, code.len);
}
local_sym.st_size = code.len;
local_sym.st_name = try self.updateString(local_sym.st_name, mem.sliceTo(decl.name, 0));
local_sym.st_info = (elf.STB_LOCAL << 4) | stt_bits;
local_sym.st_other = 0;
local_sym.st_shndx = self.text_section_index.?;
local_sym.st_shndx = block_list.section_index.?;
// TODO this write could be avoided if no fields of the symbol were changed.
try self.writeSymbol(decl.link.elf.local_sym_index);
} else {
const decl_name = mem.sliceTo(decl.name, 0);
const name_str_index = try self.makeString(decl_name);
const vaddr = try self.allocateTextBlock(&decl.link.elf, code.len, required_alignment);
const vaddr = try self.allocateTextBlock(block_list, &decl.link.elf, code.len, required_alignment);
errdefer self.freeTextBlock(block_list, &decl.link.elf);
log.debug("allocated text block for {s} at 0x{x}", .{ decl_name, vaddr });
errdefer self.freeTextBlock(&decl.link.elf);
errdefer self.freeTextBlock(block_list, &decl.link.elf);
local_sym.* = .{
.st_name = name_str_index,
.st_info = (elf.STB_LOCAL << 4) | stt_bits,
.st_other = 0,
.st_shndx = self.text_section_index.?,
.st_shndx = block_list.section_index.?,
.st_value = vaddr,
.st_size = code.len,
};
@ -2263,8 +2327,8 @@ fn updateDeclCode(self: *Elf, decl: *Module.Decl, code: []const u8, stt_bits: u8
try self.writeOffsetTableEntry(decl.link.elf.offset_table_index);
}
const section_offset = local_sym.st_value - self.program_headers.items[self.phdr_load_re_index.?].p_vaddr;
const file_offset = self.sections.items[self.text_section_index.?].sh_offset + section_offset;
const section_offset = local_sym.st_value - self.program_headers.items[block_list.phdr_index.?].p_vaddr;
const file_offset = self.sections.items[block_list.section_index.?].sh_offset + section_offset;
try self.base.file.?.pwriteAll(code, file_offset);
return local_sym;
@ -2772,6 +2836,8 @@ pub fn updateDeclExports(
if (decl.link.elf.local_sym_index == 0) return;
const decl_sym = self.local_symbols.items[decl.link.elf.local_sym_index];
const block_list = self.getDeclBlockList(decl);
for (exports) |exp| {
if (exp.options.section) |section_name| {
if (!mem.eql(u8, section_name, ".text")) {
@ -2808,7 +2874,7 @@ pub fn updateDeclExports(
.st_name = try self.updateString(sym.st_name, exp.options.name),
.st_info = (stb_bits << 4) | stt_bits,
.st_other = 0,
.st_shndx = self.text_section_index.?,
.st_shndx = block_list.section_index.?,
.st_value = decl_sym.st_value,
.st_size = decl_sym.st_size,
};
@ -2822,7 +2888,7 @@ pub fn updateDeclExports(
.st_name = name,
.st_info = (stb_bits << 4) | stt_bits,
.st_other = 0,
.st_shndx = self.text_section_index.?,
.st_shndx = block_list.section_index.?,
.st_value = decl_sym.st_value,
.st_size = decl_sym.st_size,
};