authorgravatar for kubkon@jakubkonka.comJakub Konka <kubkon@jakubkonka.com> 2023-10-24 17:41:28+02:00
committergravatar for jacobly@ziglang.orgJacob Young <jacobly@ziglang.org> 2023-10-25 04:27:44-04:00
loge1248b693ff53266d20d6fc88a9c70a13432322f
tree550f5fd31f8ae88442e9b1aa974e8cb0819f5789
parent0a04bd87bab4842dbf63133952d1d6eee3aa46bc

elf: allocate PHDR table always succeeding the EHDR

While this is a less flexible approach to being able to allocated the PHDR anywhere in file, it is sadly generally expected by the tooling in the wild.

1 files changed, 28 insertions(+), 17 deletions(-)

src/link/Elf.zig+28-17
......@@ -48,7 +48,7 @@ phdr_zig_load_zerofill_index: ?u16 = null,
4848/// PT_PHDR
4949phdr_table_index: ?u16 = null,
5050/// PT_LOAD for PHDR table
51/// We add this special load segment to ensure the PHDR table is always
51/// We add this special load segment to ensure the EHDR and PHDR table are always
5252/// loaded into memory.
5353phdr_table_load_index: ?u16 = null,
5454/// PT_INTERP
......@@ -289,22 +289,28 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
289289 .p64 => @alignOf(elf.Elf64_Phdr),
290290 };
291291 const image_base = self.calcImageBase();
292 const offset: u64 = switch (self.ptr_width) {
292 const ehdr_size: u64 = switch (self.ptr_width) {
293293 .p32 => @sizeOf(elf.Elf32_Ehdr),
294294 .p64 => @sizeOf(elf.Elf64_Ehdr),
295295 };
296 const reserved: u64 = 2 * self.page_size;
296297 self.phdr_table_index = try self.addPhdr(.{
297298 .type = elf.PT_PHDR,
298299 .flags = elf.PF_R,
299300 .@"align" = p_align,
300 .addr = image_base + offset,
301 .offset = offset,
301 .addr = image_base + ehdr_size,
302 .offset = ehdr_size,
303 .filesz = reserved,
304 .memsz = reserved,
302305 });
303306 self.phdr_table_load_index = try self.addPhdr(.{
304307 .type = elf.PT_LOAD,
305308 .flags = elf.PF_R,
306309 .@"align" = self.page_size,
307310 .addr = image_base,
311 .offset = 0,
312 .filesz = reserved + ehdr_size,
313 .memsz = reserved + ehdr_size,
308314 });
309315 }
310316
......@@ -870,10 +876,10 @@ pub fn growAllocSection(self: *Elf, shdr_index: u16, needed_size: u64) !void {
870876 const is_zerofill = shdr.sh_type == elf.SHT_NOBITS;
871877
872878 if (needed_size > self.allocatedSize(shdr.sh_offset) and !is_zerofill) {
873 // Must move the entire section.
874 const new_offset = self.findFreeSpace(needed_size, self.page_size);
875879 const existing_size = shdr.sh_size;
876880 shdr.sh_size = 0;
881 // Must move the entire section.
882 const new_offset = self.findFreeSpace(needed_size, self.page_size);
877883
878884 log.debug("new '{s}' file offset 0x{x} to 0x{x}", .{
879885 self.shstrtab.getAssumeExists(shdr.sh_name),
......@@ -1602,7 +1608,7 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
16021608 try self.setVersionSymtab();
16031609 try self.updateSectionSizes();
16041610
1605 self.allocatePhdrTable();
1611 try self.allocatePhdrTable();
16061612 try self.allocateAllocSections();
16071613 try self.sortPhdrs();
16081614 try self.allocateNonAllocSections();
......@@ -4655,30 +4661,35 @@ fn calcNumberOfSegments(self: *Elf) usize {
46554661}
46564662
46574663/// Allocates PHDR table in virtual memory and in file.
4658fn allocatePhdrTable(self: *Elf) void {
4664fn allocatePhdrTable(self: *Elf) error{OutOfMemory}!void {
46594665 const new_load_segments = self.calcNumberOfSegments();
46604666 const phdr_table = &self.phdrs.items[self.phdr_table_index.?];
46614667 const phdr_table_load = &self.phdrs.items[self.phdr_table_load_index.?];
46624668
4669 const ehsize: u64 = switch (self.ptr_width) {
4670 .p32 => @sizeOf(elf.Elf32_Ehdr),
4671 .p64 => @sizeOf(elf.Elf64_Ehdr),
4672 };
46634673 const phsize: u64 = switch (self.ptr_width) {
46644674 .p32 => @sizeOf(elf.Elf32_Phdr),
46654675 .p64 => @sizeOf(elf.Elf64_Phdr),
46664676 };
46674677 const needed_size = (self.phdrs.items.len + new_load_segments) * phsize;
4678 const available_space = self.allocatedSize(phdr_table.p_offset);
46684679
46694680 if (needed_size > self.allocatedSize(phdr_table.p_offset)) {
4670 phdr_table.p_offset = 0;
4671 phdr_table.p_offset = self.findFreeSpace(needed_size, phdr_table.p_align);
4681 // TODO in this case, we have two options:
4682 // 1. increase the available padding for EHDR + PHDR table so that we don't overflow it
4683 // (I think we are in good position to estimate required size without running out of space)
4684 // 2. shift everything in file to free more space for EHDR + PHDR table
4685 var err = try self.addErrorWithNotes(1);
4686 try err.addMsg(self, "fatal linker error: not enough space reserved for EHDR and PHDR table", .{});
4687 try err.addNote(self, "required 0x{x}, available 0x{x}", .{ needed_size, available_space });
46724688 }
46734689
4674 phdr_table_load.p_offset = mem.alignBackward(u64, phdr_table.p_offset, phdr_table_load.p_align);
4675 const load_align_offset = phdr_table.p_offset - phdr_table_load.p_offset;
4676 phdr_table_load.p_filesz = load_align_offset + needed_size;
4677 phdr_table_load.p_memsz = load_align_offset + needed_size;
4678
4690 phdr_table_load.p_filesz = needed_size + ehsize;
4691 phdr_table_load.p_memsz = needed_size + ehsize;
46794692 phdr_table.p_filesz = needed_size;
4680 phdr_table.p_vaddr = phdr_table_load.p_vaddr + load_align_offset;
4681 phdr_table.p_paddr = phdr_table_load.p_paddr + load_align_offset;
46824693 phdr_table.p_memsz = needed_size;
46834694}
46844695