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Add mechanism for growing/shrinking text blocks

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This commit is contained in:
Jakub Konka 2020-10-10 23:08:29 +02:00
parent 0b77152faa
commit 78ec7b671d
1 changed files with 113 additions and 14 deletions
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127
src/link/MachO.zig
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@ -134,6 +134,22 @@ error_flags: File.ErrorFlags = File.ErrorFlags{},
cmd_table_dirty: bool = false,
/// A list of text blocks that have surplus capacity. This list can have false
/// positives, as functions grow and shrink over time, only sometimes being added
/// or removed from the freelist.
///
/// A text block has surplus capacity when its overcapacity value is greater than
/// minimum_text_block_size * alloc_num / alloc_den. That is, when it has so
/// much extra capacity, that we could fit a small new symbol in it, itself with
/// ideal_capacity or more.
///
/// Ideal capacity is defined by size * alloc_num / alloc_den.
///
/// Overcapacity is measured by actual_capacity - ideal_capacity. Note that
/// 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) = .{},
/// Pointer to the last allocated text block
last_text_block: ?*TextBlock = null,
@ -755,6 +771,7 @@ fn darwinArchString(arch: std.Target.Cpu.Arch) []const u8 {
}
pub fn deinit(self: *MachO) void {
self.text_block_free_list.deinit(self.base.allocator);
self.offset_table.deinit(self.base.allocator);
self.offset_table_free_list.deinit(self.base.allocator);
self.string_table.deinit(self.base.allocator);
@ -767,6 +784,61 @@ pub fn deinit(self: *MachO) void {
self.load_commands.deinit(self.base.allocator);
}
fn freeTextBlock(self: *MachO, 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);
continue;
}
if (self.text_block_free_list.items[i] == text_block.prev) {
already_have_free_list_node = true;
}
i += 1;
}
}
// TODO process free list for dbg info just like we do above for vaddrs
if (self.last_text_block == text_block) {
// TODO shrink the __text section size here
self.last_text_block = text_block.prev;
}
if (text_block.prev) |prev| {
prev.next = text_block.next;
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 {};
}
} else {
text_block.prev = null;
}
if (text_block.next) |next| {
next.prev = text_block.prev;
} else {
text_block.next = null;
}
}
fn shrinkTextBlock(self: *MachO, text_block: *TextBlock, new_block_size: u64) void {
// 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: *MachO, 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.n_value, alignment) == sym.n_value;
const need_realloc = !align_ok or new_block_size > text_block.capacity(self.*);
if (!need_realloc) return sym.n_value;
return self.allocateTextBlock(text_block, new_block_size, alignment);
}
pub fn allocateDeclIndexes(self: *MachO, decl: *Module.Decl) !void {
if (decl.link.macho.local_sym_index != 0) return;
@ -811,24 +883,51 @@ pub fn updateDecl(self: *MachO, module: *Module, decl: *Module.Decl) !void {
};
const required_alignment = typed_value.ty.abiAlignment(self.base.options.target);
assert(decl.link.macho.local_sym_index != 0); // Caller forgot to call allocateDeclIndexes()
const symbol = &self.local_symbols.items[decl.link.macho.local_sym_index];
const decl_name = mem.spanZ(decl.name);
const name_str_index = try self.makeString(decl_name);
const addr = try self.allocateTextBlock(&decl.link.macho, code.len, required_alignment);
log.debug("allocated text block for {} at 0x{x}\n", .{ decl_name, addr });
if (decl.link.macho.size != 0) {
const capacity = decl.link.macho.capacity(self.*);
const need_realloc = code.len > capacity or !mem.isAlignedGeneric(u64, symbol.n_value, required_alignment);
if (need_realloc) {
const vaddr = try self.growTextBlock(&decl.link.macho, code.len, required_alignment);
log.debug("growing {} from 0x{x} to 0x{x}\n", .{ decl.name, symbol.n_value, vaddr });
if (vaddr != symbol.n_value) {
symbol.n_value = vaddr;
symbol.* = .{
.n_strx = name_str_index,
.n_type = macho.N_SECT,
.n_sect = @intCast(u8, self.text_section_index.?) + 1,
.n_desc = 0,
.n_value = addr,
};
self.offset_table.items[decl.link.macho.offset_table_index] = addr;
log.debug(" (writing new offset table entry)\n", .{});
self.offset_table.items[decl.link.macho.offset_table_index] = vaddr;
try self.writeOffsetTableEntry(decl.link.macho.offset_table_index);
}
} else if (code.len < decl.link.macho.size) {
self.shrinkTextBlock(&decl.link.macho, code.len);
}
decl.link.macho.size = code.len;
symbol.n_strx = try self.updateString(symbol.n_strx, mem.spanZ(decl.name));
symbol.n_type = macho.N_SECT;
symbol.n_sect = @intCast(u8, self.text_section_index.?) + 1;
symbol.n_desc = 0;
// TODO this write could be avoided if no fields of the symbol were changed.
try self.writeSymbol(decl.link.macho.local_sym_index);
} else {
const decl_name = mem.spanZ(decl.name);
const name_str_index = try self.makeString(decl_name);
const addr = try self.allocateTextBlock(&decl.link.macho, code.len, required_alignment);
log.debug("allocated text block for {} at 0x{x}\n", .{ decl_name, addr });
errdefer self.freeTextBlock(&decl.link.macho);
try self.writeSymbol(decl.link.macho.local_sym_index);
try self.writeOffsetTableEntry(decl.link.macho.offset_table_index);
symbol.* = .{
.n_strx = name_str_index,
.n_type = macho.N_SECT,
.n_sect = @intCast(u8, self.text_section_index.?) + 1,
.n_desc = 0,
.n_value = addr,
};
self.offset_table.items[decl.link.macho.offset_table_index] = addr;
try self.writeSymbol(decl.link.macho.local_sym_index);
try self.writeOffsetTableEntry(decl.link.macho.offset_table_index);
}
const text_section = self.sections.items[self.text_section_index.?];
const section_offset = symbol.n_value - text_section.addr;