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elf: allocate .bss section and matching PHDR

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This commit is contained in:
Jakub Konka 2023-09-13 17:53:56 +02:00
parent 10a99f8f64
commit 9de0df76a8
1 changed files with 49 additions and 2 deletions
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51
src/link/Elf.zig
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@ -40,6 +40,8 @@ phdr_got_index: ?u16 = null,
phdr_load_ro_index: ?u16 = null,
/// The index into the program headers of a PT_LOAD program header with Write flag
phdr_load_rw_index: ?u16 = null,
/// The index into the program headers of a PT_LOAD program header with zerofill data.
phdr_load_zerofill_index: ?u16 = null,
entry_addr: ?u64 = null,
page_size: u32,
@ -56,6 +58,7 @@ got: GotSection = .{},
text_section_index: ?u16 = null,
rodata_section_index: ?u16 = null,
data_section_index: ?u16 = null,
bss_section_index: ?u16 = null,
eh_frame_section_index: ?u16 = null,
eh_frame_hdr_section_index: ?u16 = null,
dynamic_section_index: ?u16 = null,
@ -532,6 +535,26 @@ pub fn populateMissingMetadata(self: *Elf) !void {
self.phdr_table_dirty = true;
}
if (self.phdr_load_zerofill_index == null) {
self.phdr_load_zerofill_index = @as(u16, @intCast(self.phdrs.items.len));
const p_align = if (self.base.options.target.os.tag == .linux) self.page_size else @as(u16, ptr_size);
const off = self.phdrs.items[self.phdr_load_rw_index.?].p_offset;
log.debug("found PT_LOAD zerofill free space 0x{x} to 0x{x}", .{ off, off });
// TODO Same as for GOT
const addr: u32 = if (self.base.options.target.ptrBitWidth() >= 32) 0x14000000 else 0xf000;
try self.phdrs.append(gpa, .{
.p_type = elf.PT_LOAD,
.p_offset = off,
.p_filesz = 0,
.p_vaddr = addr,
.p_paddr = addr,
.p_memsz = 0,
.p_align = p_align,
.p_flags = elf.PF_R | elf.PF_W,
});
self.phdr_table_dirty = true;
}
if (self.shstrtab_section_index == null) {
self.shstrtab_section_index = @as(u16, @intCast(self.shdrs.items.len));
assert(self.shstrtab.buffer.items.len == 0);
@ -655,6 +678,26 @@ pub fn populateMissingMetadata(self: *Elf) !void {
self.shdr_table_dirty = true;
}
if (self.bss_section_index == null) {
self.bss_section_index = @as(u16, @intCast(self.shdrs.items.len));
const phdr = &self.phdrs.items[self.phdr_load_zerofill_index.?];
try self.shdrs.append(gpa, .{
.sh_name = try self.shstrtab.insert(gpa, ".bss"),
.sh_type = elf.SHT_NOBITS,
.sh_flags = elf.SHF_WRITE | 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 = @as(u16, ptr_size),
.sh_entsize = 0,
});
try self.phdr_to_shdr_table.putNoClobber(gpa, self.bss_section_index.?, self.phdr_load_zerofill_index.?);
try self.last_atom_and_free_list_table.putNoClobber(gpa, self.bss_section_index.?, .{});
self.shdr_table_dirty = true;
}
if (self.symtab_section_index == null) {
self.symtab_section_index = @as(u16, @intCast(self.shdrs.items.len));
const min_align: u16 = if (small_ptr) @alignOf(elf.Elf32_Sym) else @alignOf(elf.Elf64_Sym);
@ -868,8 +911,9 @@ pub fn growAllocSection(self: *Elf, shdr_index: u16, needed_size: u64) !void {
const shdr = &self.shdrs.items[shdr_index];
const phdr_index = self.phdr_to_shdr_table.get(shdr_index).?;
const phdr = &self.phdrs.items[phdr_index];
const is_zerofill = shdr.sh_type == elf.SHT_NOBITS;
if (needed_size > self.allocatedSize(shdr.sh_offset)) {
if (needed_size > self.allocatedSize(shdr.sh_offset) and !is_zerofill) {
// Must move the entire section.
const new_offset = self.findFreeSpace(needed_size, self.page_size);
const existing_size = if (self.last_atom_and_free_list_table.get(shdr_index)) |meta| blk: {
@ -893,7 +937,10 @@ pub fn growAllocSection(self: *Elf, shdr_index: u16, needed_size: u64) !void {
shdr.sh_size = needed_size;
phdr.p_memsz = needed_size;
phdr.p_filesz = needed_size;
if (!is_zerofill) {
phdr.p_filesz = needed_size;
}
self.markDirty(shdr_index, phdr_index);
}