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elf: allocate PHDR table always succeeding the EHDR

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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.
This commit is contained in:
Jakub Konka 2023-10-24 17:41:28 +02:00 committed by Jacob Young
parent 0a04bd87ba
commit e1248b693f
1 changed files with 28 additions and 17 deletions
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45
src/link/Elf.zig
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@ -48,7 +48,7 @@ phdr_zig_load_zerofill_index: ?u16 = null,
/// PT_PHDR
phdr_table_index: ?u16 = null,
/// PT_LOAD for PHDR table
/// We add this special load segment to ensure the PHDR table is always
/// We add this special load segment to ensure the EHDR and PHDR table are always
/// loaded into memory.
phdr_table_load_index: ?u16 = null,
/// PT_INTERP
@ -289,22 +289,28 @@ pub fn openPath(allocator: Allocator, sub_path: []const u8, options: link.Option
.p64 => @alignOf(elf.Elf64_Phdr),
};
const image_base = self.calcImageBase();
const offset: u64 = switch (self.ptr_width) {
const ehdr_size: u64 = switch (self.ptr_width) {
.p32 => @sizeOf(elf.Elf32_Ehdr),
.p64 => @sizeOf(elf.Elf64_Ehdr),
};
const reserved: u64 = 2 * self.page_size;
self.phdr_table_index = try self.addPhdr(.{
.type = elf.PT_PHDR,
.flags = elf.PF_R,
.@"align" = p_align,
.addr = image_base + offset,
.offset = offset,
.addr = image_base + ehdr_size,
.offset = ehdr_size,
.filesz = reserved,
.memsz = reserved,
});
self.phdr_table_load_index = try self.addPhdr(.{
.type = elf.PT_LOAD,
.flags = elf.PF_R,
.@"align" = self.page_size,
.addr = image_base,
.offset = 0,
.filesz = reserved + ehdr_size,
.memsz = reserved + ehdr_size,
});
}
@ -870,10 +876,10 @@ pub fn growAllocSection(self: *Elf, shdr_index: u16, needed_size: u64) !void {
const is_zerofill = shdr.sh_type == elf.SHT_NOBITS;
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 = shdr.sh_size;
shdr.sh_size = 0;
// Must move the entire section.
const new_offset = self.findFreeSpace(needed_size, self.page_size);
log.debug("new '{s}' file offset 0x{x} to 0x{x}", .{
self.shstrtab.getAssumeExists(shdr.sh_name),
@ -1602,7 +1608,7 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
try self.setVersionSymtab();
try self.updateSectionSizes();
self.allocatePhdrTable();
try self.allocatePhdrTable();
try self.allocateAllocSections();
try self.sortPhdrs();
try self.allocateNonAllocSections();
@ -4655,30 +4661,35 @@ fn calcNumberOfSegments(self: *Elf) usize {
}
/// Allocates PHDR table in virtual memory and in file.
fn allocatePhdrTable(self: *Elf) void {
fn allocatePhdrTable(self: *Elf) error{OutOfMemory}!void {
const new_load_segments = self.calcNumberOfSegments();
const phdr_table = &self.phdrs.items[self.phdr_table_index.?];
const phdr_table_load = &self.phdrs.items[self.phdr_table_load_index.?];
const ehsize: u64 = switch (self.ptr_width) {
.p32 => @sizeOf(elf.Elf32_Ehdr),
.p64 => @sizeOf(elf.Elf64_Ehdr),
};
const phsize: u64 = switch (self.ptr_width) {
.p32 => @sizeOf(elf.Elf32_Phdr),
.p64 => @sizeOf(elf.Elf64_Phdr),
};
const needed_size = (self.phdrs.items.len + new_load_segments) * phsize;
const available_space = self.allocatedSize(phdr_table.p_offset);
if (needed_size > self.allocatedSize(phdr_table.p_offset)) {
phdr_table.p_offset = 0;
phdr_table.p_offset = self.findFreeSpace(needed_size, phdr_table.p_align);
// TODO in this case, we have two options:
// 1. increase the available padding for EHDR + PHDR table so that we don't overflow it
// (I think we are in good position to estimate required size without running out of space)
// 2. shift everything in file to free more space for EHDR + PHDR table
var err = try self.addErrorWithNotes(1);
try err.addMsg(self, "fatal linker error: not enough space reserved for EHDR and PHDR table", .{});
try err.addNote(self, "required 0x{x}, available 0x{x}", .{ needed_size, available_space });
}
phdr_table_load.p_offset = mem.alignBackward(u64, phdr_table.p_offset, phdr_table_load.p_align);
const load_align_offset = phdr_table.p_offset - phdr_table_load.p_offset;
phdr_table_load.p_filesz = load_align_offset + needed_size;
phdr_table_load.p_memsz = load_align_offset + needed_size;
phdr_table_load.p_filesz = needed_size + ehsize;
phdr_table_load.p_memsz = needed_size + ehsize;
phdr_table.p_filesz = needed_size;
phdr_table.p_vaddr = phdr_table_load.p_vaddr + load_align_offset;
phdr_table.p_paddr = phdr_table_load.p_paddr + load_align_offset;
phdr_table.p_memsz = needed_size;
}