Handle section groups

README.md

@@ -9,6 +9,7 @@ Usage: zelf [options] file
 
 General Options:
 -a, --all                        Equivalent of having all flags on
+-g, --section-groups             Display the section groups
 -h, --file-header                Display ELF file header
 -l, --program-headers            Display program headers (if present)
 -S, --section-headers            Display section headers

build.zig

@@ -10,7 +10,7 @@ pub fn build(b: *std.Build) void {
 
     const exe = b.addExecutable(.{
         .name = "zelf",
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = target,
         .optimize = mode,
         .use_llvm = use_llvm,

src/Object.zig

@@ -625,6 +625,50 @@ pub fn printPhdrs(self: Object, writer: anytype) !void {
     }
 }
 
+pub fn printSectionGroups(self: Object, writer: anytype) !void {
+    const has_section_groups = for (self.shdrs.items) |shdr| switch (shdr.sh_type) {
+        elf.SHT_GROUP => break true,
+        else => {},
+    } else false;
+    if (!has_section_groups) return writer.print("There are no section groups in this file.\n", .{});
+
+    for (self.shdrs.items, 0..) |shdr, i| switch (shdr.sh_type) {
+        elf.SHT_GROUP => {
+            const raw = self.getSectionContents(shdr);
+            const num_members = std.math.divExact(usize, raw.len, @sizeOf(u32)) catch {
+                // TODO convert into an error
+                return writer.print("Section {d}, '{s}' does not divide by group member size.\n", .{
+                    i, self.getShString(shdr.sh_name),
+                });
+            };
+            if (num_members == 0) return writer.print("Empty section {d}, '{s}'.\n", .{
+                i, self.getShString(shdr.sh_name),
+            });
+            const members = @as([*]align(1) const u32, @ptrCast(raw.ptr))[0..num_members];
+            if (members[0] != elf.GRP_COMDAT) return writer.print("Unknown SHT_GROUP format in section {d}, '{s}'.\n", .{
+                i, self.getShString(shdr.sh_name),
+            });
+            const group_info_sym = self.symtab.items[shdr.sh_info];
+            const group_signature = if (group_info_sym.st_name == 0 and group_info_sym.st_type() == elf.STT_SECTION)
+                self.getShString(self.shdrs.items[group_info_sym.st_shndx].sh_name)
+            else
+                getString(self.strtab, group_info_sym.st_name);
+            try writer.print("COMDAT group section [{d: >5}] `{s}' [{s}] contains {d} sections:\n", .{
+                i, self.getShString(shdr.sh_name), group_signature, num_members - 1,
+            });
+            try writer.writeAll("   [Index]    Name\n");
+            for (members[1..], 1..) |shndx, n| {
+                try writer.print("   [{d: >5}]   {s}", .{
+                    shndx,
+                    self.getShString(self.shdrs.items[shndx].sh_name),
+                });
+                if (n < members.len - 1) try writer.writeByte('\n');
+            }
+        },
+        else => {},
+    };
+}
+
 pub fn printRelocs(self: Object, writer: anytype) !void {
     const has_relocs = for (self.shdrs.items) |shdr| switch (shdr.sh_type) {
         elf.SHT_RELA, elf.SHT_REL => break true,

src/main.zig

@@ -12,6 +12,7 @@ const usage =
     \\
     \\General Options:
     \\-a, --all                        Equivalent of having all flags on
+    \\-g, --section-groups             Display the section groups
     \\-h, --file-header                Display ELF file header
     \\-l, --program-headers            Display program headers (if present)
     \\-S, --section-headers            Display section headers
@@ -139,6 +140,7 @@ pub fn main() anyerror!void {
                 '-' => break :blk,
                 'a' => tmp = PrintMatrix.enableAll(),
                 'c' => tmp.archive_index = true,
+                'g' => tmp.section_groups = true,
                 'h' => tmp.header = true,
                 'l' => tmp.phdrs = true,
                 'S' => tmp.shdrs = true,
@@ -166,6 +168,8 @@ pub fn main() anyerror!void {
             print_matrix.phdrs = true;
         } else if (p.flag2("section-headers")) {
             print_matrix.shdrs = true;
+        } else if (p.flag2("section-groups")) {
+            print_matrix.section_groups = true;
         } else if (p.flag2("symbols")) {
             print_matrix.dynamic_symbols = true;
             print_matrix.symbols = true;
@@ -264,6 +268,10 @@ fn printObject(object: Object, print_matrix: PrintMatrix, arg_data: ArgData, std
         try object.printPhdrs(stdout);
         try stdout.writeAll("\n");
     }
+    if (print_matrix.section_groups) {
+        try object.printSectionGroups(stdout);
+        try stdout.writeAll("\n");
+    }
     if (print_matrix.relocs) {
         try object.printRelocs(stdout);
         try stdout.writeAll("\n");
@@ -319,6 +327,7 @@ const PrintMatrix = packed struct {
     archive_index: bool = false,
     phdrs: bool = false,
     shdrs: bool = false,
+    section_groups: bool = false,
     symbols: bool = false,
     dynamic_symbols: bool = false,
     dynamic_section: bool = false,
@@ -346,6 +355,7 @@ const PrintMatrix = packed struct {
             .archive_index = true,
             .phdrs = true,
             .shdrs = true,
+            .section_groups = true,
             .symbols = true,
             .dynamic_symbols = true,
             .dynamic_section = true,