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plan9 linker: add free lists for got_index and sym_index

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This allows the same global offset and symbol table index to be re-used
if a decl is freed.
This commit is contained in:
Jacob G-W 2021-08-29 16:35:52 -04:00
parent f388b57553
commit 4cb2d6bc3e
1 changed files with 30 additions and 11 deletions
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41
src/link/Plan9.zig
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@ -39,6 +39,11 @@ magic: u32,
entry_val: ?u64 = null,
got_len: usize = 0,
// A list of all the free got indexes, so when making a new decl
// don't make a new one, just use one from here.
got_index_free_list: std.ArrayListUnmanaged(u64) = .{},
syms_index_free_list: std.ArrayListUnmanaged(u64) = .{},
const Bases = struct {
text: u64,
@ -212,8 +217,12 @@ fn updateFinish(self: *Plan9, decl: *Module.Decl) !void {
if (decl.link.plan9.sym_index) |s| {
self.syms.items[s] = sym;
} else {
try self.syms.append(self.base.allocator, sym);
decl.link.plan9.sym_index = self.syms.items.len - 1;
if (self.syms_index_free_list.popOrNull()) |i| {
decl.link.plan9.sym_index = i;
} else {
try self.syms.append(self.base.allocator, sym);
decl.link.plan9.sym_index = self.syms.items.len - 1;
}
}
}
@ -244,14 +253,12 @@ pub fn flushModule(self: *Plan9, comp: *Compilation) !void {
const mod = self.base.options.module orelse return error.LinkingWithoutZigSourceUnimplemented;
// TODO I changed this assert from == to >= but this code all needs to be audited; see
// the comment in `freeDecl`.
assert(self.got_len >= self.fn_decl_table.count() + self.data_decl_table.count());
assert(self.got_len == self.fn_decl_table.count() + self.data_decl_table.count() + self.got_index_free_list.items.len);
const got_size = self.got_len * if (!self.sixtyfour_bit) @as(u32, 4) else 8;
var got_table = try self.base.allocator.alloc(u8, got_size);
defer self.base.allocator.free(got_table);
// + 2 for header, got, symbols
// + 3 for header, got, symbols
var iovecs = try self.base.allocator.alloc(std.os.iovec_const, self.fn_decl_table.count() + self.data_decl_table.count() + 3);
defer self.base.allocator.free(iovecs);
@ -380,18 +387,24 @@ fn addDeclExports(
}
pub fn freeDecl(self: *Plan9, decl: *Module.Decl) void {
// TODO this is not the correct check for being function body,
// it could just be a function pointer.
// TODO audit the lifetimes of decls table entries. It's possible to get
// allocateDeclIndexes and then freeDecl without any updateDecl in between.
// However that is planned to change, see the TODO comment in Module.zig
// in the deleteUnusedDecl function.
const is_fn = (decl.ty.zigTypeTag() == .Fn);
const is_fn = (decl.val.tag() == .function);
if (is_fn) {
_ = self.fn_decl_table.swapRemove(decl);
} else {
_ = self.data_decl_table.swapRemove(decl);
}
if (decl.link.plan9.got_index) |i| {
// TODO: if this catch {} is triggered, an assertion in flushModule will be triggered, because got_index_free_list will have the wrong length
self.got_index_free_list.append(self.base.allocator, i) catch {};
}
if (decl.link.plan9.sym_index) |i| {
self.syms_index_free_list.append(self.base.allocator, i) catch {};
self.syms.items[i] = undefined;
}
}
pub fn updateDeclExports(
@ -418,6 +431,8 @@ pub fn deinit(self: *Plan9) void {
}
self.data_decl_table.deinit(self.base.allocator);
self.syms.deinit(self.base.allocator);
self.got_index_free_list.deinit(self.base.allocator);
self.syms_index_free_list.deinit(self.base.allocator);
}
pub const Export = ?usize;
@ -481,7 +496,11 @@ pub fn writeSyms(self: *Plan9, buf: *std.ArrayList(u8)) !void {
pub fn allocateDeclIndexes(self: *Plan9, decl: *Module.Decl) !void {
if (decl.link.plan9.got_index == null) {
self.got_len += 1;
decl.link.plan9.got_index = self.got_len - 1;
if (self.got_index_free_list.popOrNull()) |i| {
decl.link.plan9.got_index = i;
} else {
self.got_len += 1;
decl.link.plan9.got_index = self.got_len - 1;
}
}
}