Commit 9ccd94d560

Jakub Konka <kubkon@jakubkonka.com>
2023-10-03 16:40:39
elf: refactor object.shdrContents to never error out
1 parent 5334054
src/link/Elf/Atom.zig
@@ -49,7 +49,7 @@ pub fn file(self: Atom, elf_file: *Elf) ?File {
     return elf_file.file(self.file_index);
 }
 
-pub fn inputShdr(self: Atom, elf_file: *Elf) elf.Elf64_Shdr {
+pub fn inputShdr(self: Atom, elf_file: *Elf) Object.ElfShdr {
     const object = self.file(elf_file).?.object;
     return object.shdrs.items[self.input_section_index];
 }
@@ -272,7 +272,7 @@ pub fn free(self: *Atom, elf_file: *Elf) void {
     self.* = .{};
 }
 
-pub fn relocs(self: Atom, elf_file: *Elf) error{Overflow}![]align(1) const elf.Elf64_Rela {
+pub fn relocs(self: Atom, elf_file: *Elf) []align(1) const elf.Elf64_Rela {
     return switch (self.file(elf_file).?) {
         .zig_module => |x| x.relocs.items[self.relocs_section_index].items,
         .object => |x| x.getRelocs(self.relocs_section_index),
@@ -280,6 +280,18 @@ pub fn relocs(self: Atom, elf_file: *Elf) error{Overflow}![]align(1) const elf.E
     };
 }
 
+pub fn fdes(self: Atom, elf_file: *Elf) []Fde {
+    if (self.fde_start == self.fde_end) return &[0]Fde{};
+    const object = self.file(elf_file).?.object;
+    return object.fdes.items[self.fde_start..self.fde_end];
+}
+
+pub fn markFdesDead(self: Atom, elf_file: *Elf) void {
+    for (self.fdes(elf_file)) |*fde| {
+        fde.alive = false;
+    }
+}
+
 pub fn addReloc(self: Atom, elf_file: *Elf, reloc: elf.Elf64_Rela) !void {
     const gpa = elf_file.base.allocator;
     const file_ptr = self.file(elf_file).?;
@@ -296,8 +308,8 @@ pub fn freeRelocs(self: Atom, elf_file: *Elf) void {
     zig_module.relocs.items[self.relocs_section_index].clearRetainingCapacity();
 }
 
-pub fn scanRelocsRequiresCode(self: Atom, elf_file: *Elf) error{Overflow}!bool {
-    for (try self.relocs(elf_file)) |rel| {
+pub fn scanRelocsRequiresCode(self: Atom, elf_file: *Elf) bool {
+    for (self.relocs(elf_file)) |rel| {
         if (rel.r_type() == elf.R_X86_64_GOTTPOFF) return true;
     }
     return false;
@@ -306,7 +318,7 @@ pub fn scanRelocsRequiresCode(self: Atom, elf_file: *Elf) error{Overflow}!bool {
 pub fn scanRelocs(self: Atom, elf_file: *Elf, code: ?[]const u8, undefs: anytype) !void {
     const is_dyn_lib = elf_file.isDynLib();
     const file_ptr = self.file(elf_file).?;
-    const rels = try self.relocs(elf_file);
+    const rels = self.relocs(elf_file);
     var i: usize = 0;
     while (i < rels.len) : (i += 1) {
         const rel = rels[i];
@@ -456,7 +468,7 @@ pub fn resolveRelocs(self: Atom, elf_file: *Elf, code: []u8) !void {
     var stream = std.io.fixedBufferStream(code);
     const cwriter = stream.writer();
 
-    const rels = try self.relocs(elf_file);
+    const rels = self.relocs(elf_file);
     var i: usize = 0;
     while (i < rels.len) : (i += 1) {
         const rel = rels[i];
@@ -841,11 +853,14 @@ const x86_64 = struct {
 const std = @import("std");
 const assert = std.debug.assert;
 const elf = std.elf;
+const eh_frame = @import("eh_frame.zig");
 const log = std.log.scoped(.link);
 const relocs_log = std.log.scoped(.link_relocs);
 
 const Allocator = std.mem.Allocator;
 const Atom = @This();
 const Elf = @import("../Elf.zig");
+const Fde = eh_frame.Fde;
 const File = @import("file.zig").File;
+const Object = @import("Object.zig");
 const Symbol = @import("Symbol.zig");
src/link/Elf/eh_frame.zig
@@ -20,9 +20,9 @@ pub const Fde = struct {
         return base + fde.out_offset;
     }
 
-    pub fn data(fde: Fde, elf_file: *Elf) error{Overflow}![]const u8 {
+    pub fn data(fde: Fde, elf_file: *Elf) []const u8 {
         const object = elf_file.file(fde.file_index).?.object;
-        const contents = try object.shdrContents(fde.input_section_index);
+        const contents = object.shdrContents(fde.input_section_index);
         return contents[fde.offset..][0..fde.calcSize()];
     }
 
@@ -32,24 +32,25 @@ pub const Fde = struct {
     }
 
     pub fn ciePointer(fde: Fde, elf_file: *Elf) u32 {
-        return std.mem.readIntLittle(u32, fde.data(elf_file)[4..8]);
+        const fde_data = fde.data(elf_file);
+        return std.mem.readIntLittle(u32, fde_data[4..8]);
     }
 
     pub fn calcSize(fde: Fde) u64 {
         return fde.size + 4;
     }
 
-    pub fn atom(fde: Fde, elf_file: *Elf) error{Overflow}!*Atom {
+    pub fn atom(fde: Fde, elf_file: *Elf) *Atom {
         const object = elf_file.file(fde.file_index).?.object;
-        const rel = (try fde.relocs(elf_file))[0];
+        const rel = fde.relocs(elf_file)[0];
         const sym = object.symtab[rel.r_sym()];
         const atom_index = object.atoms.items[sym.st_shndx];
         return elf_file.atom(atom_index).?;
     }
 
-    pub fn relocs(fde: Fde, elf_file: *Elf) error{Overflow}![]align(1) const elf.Elf64_Rela {
+    pub fn relocs(fde: Fde, elf_file: *Elf) []align(1) const elf.Elf64_Rela {
         const object = elf_file.file(fde.file_index).?.object;
-        return (try object.getRelocs(fde.rel_section_index))[fde.rel_index..][0..fde.rel_num];
+        return object.getRelocs(fde.rel_section_index)[fde.rel_index..][0..fde.rel_num];
     }
 
     pub fn format(
@@ -88,10 +89,7 @@ pub const Fde = struct {
         const fde = ctx.fde;
         const elf_file = ctx.elf_file;
         const base_addr = fde.address(elf_file);
-        const atom_name = if (fde.atom(elf_file)) |atom_ptr|
-            atom_ptr.name(elf_file)
-        else |_|
-            "";
+        const atom_name = fde.atom(elf_file).name(elf_file);
         try writer.print("@{x} : size({x}) : cie({d}) : {s}", .{
             base_addr + fde.out_offset,
             fde.calcSize(),
@@ -123,9 +121,9 @@ pub const Cie = struct {
         return base + cie.out_offset;
     }
 
-    pub fn data(cie: Cie, elf_file: *Elf) error{Overflow}![]const u8 {
+    pub fn data(cie: Cie, elf_file: *Elf) []const u8 {
         const object = elf_file.file(cie.file_index).?.object;
-        const contents = try object.shdrContents(cie.input_section_index);
+        const contents = object.shdrContents(cie.input_section_index);
         return contents[cie.offset..][0..cie.calcSize()];
     }
 
@@ -133,16 +131,16 @@ pub const Cie = struct {
         return cie.size + 4;
     }
 
-    pub fn relocs(cie: Cie, elf_file: *Elf) error{Overflow}![]align(1) const elf.Elf64_Rela {
+    pub fn relocs(cie: Cie, elf_file: *Elf) []align(1) const elf.Elf64_Rela {
         const object = elf_file.file(cie.file_index).?.object;
-        return (try object.getRelocs(cie.rel_section_index))[cie.rel_index..][0..cie.rel_num];
+        return object.getRelocs(cie.rel_section_index)[cie.rel_index..][0..cie.rel_num];
     }
 
-    pub fn eql(cie: Cie, other: Cie, elf_file: *Elf) error{Overflow}!bool {
-        if (!std.mem.eql(u8, try cie.data(elf_file), try other.data(elf_file))) return false;
+    pub fn eql(cie: Cie, other: Cie, elf_file: *Elf) bool {
+        if (!std.mem.eql(u8, cie.data(elf_file), other.data(elf_file))) return false;
 
-        const cie_relocs = try cie.relocs(elf_file);
-        const other_relocs = try other.relocs(elf_file);
+        const cie_relocs = cie.relocs(elf_file);
+        const other_relocs = other.relocs(elf_file);
         if (cie_relocs.len != other_relocs.len) return false;
 
         for (cie_relocs, other_relocs) |cie_rel, other_rel| {
@@ -152,8 +150,8 @@ pub const Cie = struct {
 
             const cie_object = elf_file.file(cie.file_index).?.object;
             const other_object = elf_file.file(other.file_index).?.object;
-            const cie_sym = cie_object.symbol(cie_rel.r_sym(), elf_file);
-            const other_sym = other_object.symbol(other_rel.r_sym(), elf_file);
+            const cie_sym = cie_object.symbols.items[cie_rel.r_sym()];
+            const other_sym = other_object.symbols.items[other_rel.r_sym()];
             if (!std.mem.eql(u8, std.mem.asBytes(&cie_sym), std.mem.asBytes(&other_sym))) return false;
         }
         return true;
@@ -319,10 +317,10 @@ pub fn writeEhFrame(elf_file: *Elf, writer: anytype) !void {
         for (object.cies.items) |cie| {
             if (!cie.alive) continue;
 
-            const contents = try gpa.dupe(u8, try cie.data(elf_file));
+            const contents = try gpa.dupe(u8, cie.data(elf_file));
             defer gpa.free(contents);
 
-            for (try cie.relocs(elf_file)) |rel| {
+            for (cie.relocs(elf_file)) |rel| {
                 const sym = object.symbol(rel.r_sym(), elf_file);
                 try resolveReloc(cie, sym, rel, elf_file, contents);
             }
@@ -337,7 +335,7 @@ pub fn writeEhFrame(elf_file: *Elf, writer: anytype) !void {
         for (object.fdes.items) |fde| {
             if (!fde.alive) continue;
 
-            const contents = try gpa.dupe(u8, try fde.data(elf_file));
+            const contents = try gpa.dupe(u8, fde.data(elf_file));
             defer gpa.free(contents);
 
             std.mem.writeIntLittle(
@@ -346,7 +344,7 @@ pub fn writeEhFrame(elf_file: *Elf, writer: anytype) !void {
                 @as(i32, @truncate(@as(i64, @intCast(fde.out_offset + 4)) - @as(i64, @intCast(fde.cie(elf_file).out_offset)))),
             );
 
-            for (try fde.relocs(elf_file)) |rel| {
+            for (fde.relocs(elf_file)) |rel| {
                 const sym = object.symbol(rel.r_sym(), elf_file);
                 try resolveReloc(fde, sym, rel, elf_file, contents);
             }
@@ -395,7 +393,7 @@ pub fn writeEhFrameHdr(elf_file: *Elf, writer: anytype) !void {
         for (object.fdes.items) |fde| {
             if (!fde.alive) continue;
 
-            const relocs = try fde.relocs(elf_file);
+            const relocs = fde.relocs(elf_file);
             assert(relocs.len > 0); // Should this be an error? Things are completely broken anyhow if this trips...
             const rel = relocs[0];
             const sym = object.symbol(rel.r_sym(), elf_file);
src/link/Elf/Object.zig
@@ -4,7 +4,7 @@ data: []const u8,
 index: File.Index,
 
 header: ?elf.Elf64_Ehdr = null,
-shdrs: std.ArrayListUnmanaged(elf.Elf64_Shdr) = .{},
+shdrs: std.ArrayListUnmanaged(ElfShdr) = .{},
 strings: StringTable(.object_strings) = .{},
 symtab: []align(1) const elf.Elf64_Sym = &[0]elf.Elf64_Sym{},
 strtab: []const u8 = &[0]u8{},
@@ -64,8 +64,13 @@ pub fn parse(self: *Object, elf_file: *Elf) !void {
         [*]align(1) const elf.Elf64_Shdr,
         @ptrCast(self.data.ptr + shoff),
     )[0..self.header.?.e_shnum];
-    try self.shdrs.appendUnalignedSlice(gpa, shdrs);
-    try self.strings.buffer.appendSlice(gpa, try self.shdrContents(self.header.?.e_shstrndx));
+    try self.shdrs.ensureTotalCapacityPrecise(gpa, shdrs.len);
+
+    for (shdrs) |shdr| {
+        self.shdrs.appendAssumeCapacity(try ElfShdr.fromElf64Shdr(shdr));
+    }
+
+    try self.strings.buffer.appendSlice(gpa, self.shdrContents(self.header.?.e_shstrndx));
 
     const symtab_index = for (self.shdrs.items, 0..) |shdr, i| switch (shdr.sh_type) {
         elf.SHT_SYMTAB => break @as(u16, @intCast(i)),
@@ -76,21 +81,21 @@ pub fn parse(self: *Object, elf_file: *Elf) !void {
         const shdr = shdrs[index];
         self.first_global = shdr.sh_info;
 
-        const symtab = try self.shdrContents(index);
+        const symtab = self.shdrContents(index);
         const nsyms = @divExact(symtab.len, @sizeOf(elf.Elf64_Sym));
         self.symtab = @as([*]align(1) const elf.Elf64_Sym, @ptrCast(symtab.ptr))[0..nsyms];
-        self.strtab = try self.shdrContents(@as(u16, @intCast(shdr.sh_link)));
+        self.strtab = self.shdrContents(@as(u16, @intCast(shdr.sh_link)));
     }
 
     try self.initAtoms(elf_file);
     try self.initSymtab(elf_file);
 
-    // for (self.shdrs.items, 0..) |shdr, i| {
-    //     const atom = elf_file.atom(self.atoms.items[i]) orelse continue;
-    //     if (!atom.alive) continue;
-    //     if (shdr.sh_type == elf.SHT_X86_64_UNWIND or mem.eql(u8, atom.name(elf_file), ".eh_frame"))
-    //         try self.parseEhFrame(@as(u16, @intCast(i)), elf_file);
-    // }
+    for (self.shdrs.items, 0..) |shdr, i| {
+        const atom = elf_file.atom(self.atoms.items[i]) orelse continue;
+        if (!atom.flags.alive) continue;
+        if (shdr.sh_type == elf.SHT_X86_64_UNWIND or mem.eql(u8, atom.name(elf_file), ".eh_frame"))
+            try self.parseEhFrame(@as(u16, @intCast(i)), elf_file);
+    }
 }
 
 fn initAtoms(self: *Object, elf_file: *Elf) !void {
@@ -120,7 +125,7 @@ fn initAtoms(self: *Object, elf_file: *Elf) !void {
                 };
 
                 const shndx = @as(u16, @intCast(i));
-                const group_raw_data = try self.shdrContents(shndx);
+                const group_raw_data = self.shdrContents(shndx);
                 const group_nmembers = @divExact(group_raw_data.len, @sizeOf(u32));
                 const group_members = @as([*]align(1) const u32, @ptrCast(group_raw_data.ptr))[0..group_nmembers];
 
@@ -173,11 +178,11 @@ fn initAtoms(self: *Object, elf_file: *Elf) !void {
 
 fn addAtom(
     self: *Object,
-    shdr: elf.Elf64_Shdr,
+    shdr: ElfShdr,
     shndx: u16,
     name: [:0]const u8,
     elf_file: *Elf,
-) error{ OutOfMemory, Overflow }!void {
+) error{OutOfMemory}!void {
     const atom_index = try elf_file.addAtom();
     const atom = elf_file.atom(atom_index).?;
     atom.atom_index = atom_index;
@@ -188,7 +193,7 @@ fn addAtom(
     self.atoms.items[shndx] = atom_index;
 
     if (shdr.sh_flags & elf.SHF_COMPRESSED != 0) {
-        const data = try self.shdrContents(shndx);
+        const data = self.shdrContents(shndx);
         const chdr = @as(*align(1) const elf.Elf64_Chdr, @ptrCast(data.ptr)).*;
         atom.size = chdr.ch_size;
         atom.alignment = Alignment.fromNonzeroByteUnits(chdr.ch_addralign);
@@ -198,7 +203,7 @@ fn addAtom(
     }
 }
 
-fn initOutputSection(self: Object, elf_file: *Elf, shdr: elf.Elf64_Shdr) error{OutOfMemory}!u16 {
+fn initOutputSection(self: Object, elf_file: *Elf, shdr: ElfShdr) error{OutOfMemory}!u16 {
     const name = blk: {
         const name = self.strings.getAssumeExists(shdr.sh_name);
         if (shdr.sh_flags & elf.SHF_MERGE != 0) break :blk name;
@@ -244,7 +249,6 @@ fn initOutputSection(self: Object, elf_file: *Elf, shdr: elf.Elf64_Shdr) error{O
 }
 
 fn skipShdr(self: *Object, index: u16, elf_file: *Elf) bool {
-    _ = elf_file;
     const shdr = self.shdrs.items[index];
     const name = self.strings.getAssumeExists(shdr.sh_name);
     const ignore = blk: {
@@ -252,9 +256,8 @@ fn skipShdr(self: *Object, index: u16, elf_file: *Elf) bool {
         if (mem.startsWith(u8, name, ".comment")) break :blk true;
         if (mem.startsWith(u8, name, ".llvm_addrsig")) break :blk true;
         if (mem.startsWith(u8, name, ".eh_frame")) break :blk true;
-        // if (elf_file.base.options.strip and shdr.sh_flags & elf.SHF_ALLOC == 0 and
-        //     mem.startsWith(u8, name, ".debug")) break :blk true;
-        if (shdr.sh_flags & elf.SHF_ALLOC == 0 and mem.startsWith(u8, name, ".debug")) break :blk true;
+        if (elf_file.base.options.strip and shdr.sh_flags & elf.SHF_ALLOC == 0 and
+            mem.startsWith(u8, name, ".debug")) break :blk true;
         break :blk false;
     };
     return ignore;
@@ -303,8 +306,8 @@ fn parseEhFrame(self: *Object, shndx: u16, elf_file: *Elf) !void {
     };
 
     const gpa = elf_file.base.allocator;
-    const raw = try self.shdrContents(shndx);
-    const relocs = try self.getRelocs(relocs_shndx);
+    const raw = self.shdrContents(shndx);
+    const relocs = self.getRelocs(relocs_shndx);
     const fdes_start = self.fdes.items.len;
     const cies_start = self.cies.items.len;
 
@@ -408,7 +411,7 @@ pub fn scanRelocs(self: *Object, elf_file: *Elf, undefs: anytype) !void {
         const shdr = atom.inputShdr(elf_file);
         if (shdr.sh_flags & elf.SHF_ALLOC == 0) continue;
         if (shdr.sh_type == elf.SHT_NOBITS) continue;
-        if (try atom.scanRelocsRequiresCode(elf_file)) {
+        if (atom.scanRelocsRequiresCode(elf_file)) {
             // TODO ideally, we don't have to decompress at this stage (should already be done)
             // and we just fetch the code slice.
             const code = try self.codeDecompressAlloc(elf_file, atom_index);
@@ -418,7 +421,7 @@ pub fn scanRelocs(self: *Object, elf_file: *Elf, undefs: anytype) !void {
     }
 
     for (self.cies.items) |cie| {
-        for (try cie.relocs(elf_file)) |rel| {
+        for (cie.relocs(elf_file)) |rel| {
             const sym = elf_file.symbol(self.symbols.items[rel.r_sym()]);
             if (sym.flags.import) {
                 if (sym.type(elf_file) != elf.STT_FUNC)
@@ -518,6 +521,15 @@ pub fn markLive(self: *Object, elf_file: *Elf) void {
     }
 }
 
+pub fn markEhFrameAtomsDead(self: Object, elf_file: *Elf) void {
+    for (self.atoms.items) |atom_index| {
+        const atom = elf_file.atom(atom_index) orelse continue;
+        const is_eh_frame = atom.inputShdr(elf_file).sh_type == elf.SHT_X86_64_UNWIND or
+            mem.eql(u8, atom.name(elf_file), ".eh_frame");
+        if (atom.flags.alive and is_eh_frame) atom.flags.alive = false;
+    }
+}
+
 pub fn checkDuplicates(self: *Object, elf_file: *Elf) void {
     const first_global = self.first_global orelse return;
     for (self.globals(), 0..) |index, i| {
@@ -747,12 +759,10 @@ pub fn globals(self: Object) []const Symbol.Index {
     return self.symbols.items[start..];
 }
 
-fn shdrContents(self: Object, index: u32) error{Overflow}![]const u8 {
+pub fn shdrContents(self: Object, index: u32) []const u8 {
     assert(index < self.shdrs.items.len);
     const shdr = self.shdrs.items[index];
-    const offset = math.cast(usize, shdr.sh_offset) orelse return error.Overflow;
-    const size = math.cast(usize, shdr.sh_size) orelse return error.Overflow;
-    return self.data[offset..][0..size];
+    return self.data[shdr.sh_offset..][0..shdr.sh_size];
 }
 
 /// Returns atom's code and optionally uncompresses data if required (for compressed sections).
@@ -761,7 +771,7 @@ pub fn codeDecompressAlloc(self: Object, elf_file: *Elf, atom_index: Atom.Index)
     const gpa = elf_file.base.allocator;
     const atom_ptr = elf_file.atom(atom_index).?;
     assert(atom_ptr.file_index == self.index);
-    const data = try self.shdrContents(atom_ptr.input_section_index);
+    const data = self.shdrContents(atom_ptr.input_section_index);
     const shdr = atom_ptr.inputShdr(elf_file);
     if (shdr.sh_flags & elf.SHF_COMPRESSED != 0) {
         const chdr = @as(*align(1) const elf.Elf64_Chdr, @ptrCast(data.ptr)).*;
@@ -789,8 +799,8 @@ fn getString(self: *Object, off: u32) [:0]const u8 {
     return mem.sliceTo(@as([*:0]const u8, @ptrCast(self.strtab.ptr + off)), 0);
 }
 
-pub fn comdatGroupMembers(self: *Object, index: u16) error{Overflow}![]align(1) const u32 {
-    const raw = try self.shdrContents(index);
+pub fn comdatGroupMembers(self: *Object, index: u16) []align(1) const u32 {
+    const raw = self.shdrContents(index);
     const nmembers = @divExact(raw.len, @sizeOf(u32));
     const members = @as([*]align(1) const u32, @ptrCast(raw.ptr))[1..nmembers];
     return members;
@@ -800,8 +810,8 @@ pub fn asFile(self: *Object) File {
     return .{ .object = self };
 }
 
-pub fn getRelocs(self: *Object, shndx: u32) error{Overflow}![]align(1) const elf.Elf64_Rela {
-    const raw = try self.shdrContents(shndx);
+pub fn getRelocs(self: *Object, shndx: u32) []align(1) const elf.Elf64_Rela {
+    const raw = self.shdrContents(shndx);
     const num = @divExact(raw.len, @sizeOf(elf.Elf64_Rela));
     return @as([*]align(1) const elf.Elf64_Rela, @ptrCast(raw.ptr))[0..num];
 }
@@ -941,7 +951,7 @@ fn formatComdatGroups(
         const cg = elf_file.comdatGroup(cg_index);
         const cg_owner = elf_file.comdatGroupOwner(cg.owner);
         if (cg_owner.file != object.index) continue;
-        const cg_members = object.comdatGroupMembers(cg.shndx) catch continue;
+        const cg_members = object.comdatGroupMembers(cg.shndx);
         for (cg_members) |shndx| {
             const atom_index = object.atoms.items[shndx];
             const atom = elf_file.atom(atom_index) orelse continue;
@@ -970,6 +980,34 @@ fn formatPath(
     } else try writer.writeAll(object.path);
 }
 
+pub const ElfShdr = struct {
+    sh_name: u32,
+    sh_type: u32,
+    sh_flags: u64,
+    sh_addr: u64,
+    sh_offset: usize,
+    sh_size: usize,
+    sh_link: u32,
+    sh_info: u32,
+    sh_addralign: u64,
+    sh_entsize: u64,
+
+    fn fromElf64Shdr(shdr: elf.Elf64_Shdr) error{Overflow}!ElfShdr {
+        return .{
+            .sh_name = shdr.sh_name,
+            .sh_type = shdr.sh_type,
+            .sh_flags = shdr.sh_flags,
+            .sh_addr = shdr.sh_addr,
+            .sh_offset = math.cast(usize, shdr.sh_offset) orelse return error.Overflow,
+            .sh_size = math.cast(usize, shdr.sh_size) orelse return error.Overflow,
+            .sh_link = shdr.sh_link,
+            .sh_info = shdr.sh_info,
+            .sh_addralign = shdr.sh_addralign,
+            .sh_entsize = shdr.sh_entsize,
+        };
+    }
+};
+
 const Object = @This();
 
 const std = @import("std");
src/link/Elf/ZigModule.zig
@@ -145,7 +145,7 @@ pub fn scanRelocs(self: *ZigModule, elf_file: *Elf, undefs: anytype) !void {
     for (self.atoms.items) |atom_index| {
         const atom = elf_file.atom(atom_index) orelse continue;
         if (!atom.flags.alive) continue;
-        if (try atom.scanRelocsRequiresCode(elf_file)) {
+        if (atom.scanRelocsRequiresCode(elf_file)) {
             // TODO ideally we don't have to fetch the code here.
             // Perhaps it would make sense to save the code until flushModule where we
             // would free all of generated code?
src/link/Elf.zig
@@ -1235,7 +1235,8 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
     // input Object files.
     // Any qualifing unresolved symbol will be upgraded to an absolute, weak
     // symbol for potential resolution at load-time.
-    try self.resolveSymbols();
+    self.resolveSymbols();
+    self.markEhFrameAtomsDead();
     self.markImportsExports();
     self.claimUnresolved();
 
@@ -1610,7 +1611,7 @@ fn parseArchive(
 /// 4. Reset state of all resolved globals since we will redo this bit on the pruned set.
 /// 5. Remove references to dead objects/shared objects
 /// 6. Re-run symbol resolution on pruned objects and shared objects sets.
-fn resolveSymbols(self: *Elf) error{Overflow}!void {
+fn resolveSymbols(self: *Elf) void {
     // Resolve symbols in the ZigModule. For now, we assume that it's always live.
     if (self.zig_module_index) |index| self.file(index).?.resolveSymbols(self);
     // Resolve symbols on the set of all objects and shared objects (even if some are unneeded).
@@ -1652,11 +1653,11 @@ fn resolveSymbols(self: *Elf) error{Overflow}!void {
             const cg = self.comdatGroup(cg_index);
             const cg_owner = self.comdatGroupOwner(cg.owner);
             if (cg_owner.file != index) {
-                for (try object.comdatGroupMembers(cg.shndx)) |shndx| {
+                for (object.comdatGroupMembers(cg.shndx)) |shndx| {
                     const atom_index = object.atoms.items[shndx];
                     if (self.atom(atom_index)) |atom_ptr| {
                         atom_ptr.flags.alive = false;
-                        // atom_ptr.markFdesDead(self);
+                        atom_ptr.markFdesDead(self);
                     }
                 }
             }
@@ -1680,6 +1681,14 @@ fn markLive(self: *Elf) void {
     }
 }
 
+fn markEhFrameAtomsDead(self: *Elf) void {
+    for (self.objects.items) |index| {
+        const file_ptr = self.file(index).?;
+        if (!file_ptr.isAlive()) continue;
+        file_ptr.object.markEhFrameAtomsDead(self);
+    }
+}
+
 fn markImportsExports(self: *Elf) void {
     const mark = struct {
         fn mark(elf_file: *Elf, file_index: File.Index) void {
@@ -3389,17 +3398,39 @@ fn initSections(self: *Elf) !void {
         .p32 => true,
         .p64 => false,
     };
+    const ptr_size = self.ptrWidthBytes();
 
     for (self.objects.items) |index| {
         try self.file(index).?.object.initOutputSections(self);
     }
 
+    const needs_eh_frame = for (self.objects.items) |index| {
+        if (self.file(index).?.object.cies.items.len > 0) break true;
+    } else false;
+    if (needs_eh_frame) {
+        self.eh_frame_section_index = try self.addSection(.{
+            .name = ".eh_frame",
+            .type = elf.SHT_PROGBITS,
+            .flags = elf.SHF_ALLOC,
+            .addralign = ptr_size,
+        });
+
+        if (self.base.options.eh_frame_hdr) {
+            self.eh_frame_hdr_section_index = try self.addSection(.{
+                .name = ".eh_frame_hdr",
+                .type = elf.SHT_PROGBITS,
+                .flags = elf.SHF_ALLOC,
+                .addralign = ptr_size,
+            });
+        }
+    }
+
     if (self.got.entries.items.len > 0 and self.got_section_index == null) {
         self.got_section_index = try self.addSection(.{
             .name = ".got",
             .type = elf.SHT_PROGBITS,
             .flags = elf.SHF_ALLOC | elf.SHF_WRITE,
-            .addralign = self.ptrWidthBytes(),
+            .addralign = ptr_size,
         });
     }
 
@@ -3533,6 +3564,18 @@ fn updateSectionSizes(self: *Elf) !void {
         self.file(index).?.object.updateSectionSizes(self);
     }
 
+    if (self.eh_frame_section_index) |index| {
+        const shdr = &self.shdrs.items[index];
+        shdr.sh_size = try eh_frame.calcEhFrameSize(self);
+        shdr.sh_addralign = @alignOf(u64);
+    }
+
+    if (self.eh_frame_hdr_section_index) |index| {
+        const shdr = &self.shdrs.items[index];
+        shdr.sh_size = eh_frame.calcEhFrameHdrSize(self);
+        shdr.sh_addralign = @alignOf(u32);
+    }
+
     if (self.got_section_index) |index| {
         self.shdrs.items[index].sh_size = self.got.size(self);
     }
@@ -4937,6 +4980,7 @@ const math = std.math;
 const mem = std.mem;
 
 const codegen = @import("../codegen.zig");
+const eh_frame = @import("Elf/eh_frame.zig");
 const glibc = @import("../glibc.zig");
 const link = @import("../link.zig");
 const lldMain = @import("../main.zig").lldMain;