From 93f0189f14a575fbc64dd170afabbfdba63c441c Mon Sep 17 00:00:00 2001
From: "MATSUMOTO, Katsuyoshi" <github@katsyoshi.org>
Date: Thu, 2 Jul 2026 18:12:22 +0900
Subject: [PATCH] remap symbol indexes after sorting symtab

---
 lib/caotral/linker/builder.rb                | 23 +++++++++++++-------
 sample/C/mixed_external_and_libc_functions.c |  7 ++++++
 test/caotral/linker/symbol_remap_test.rb     | 19 ++++++++++++++++
 3 files changed, 41 insertions(+), 8 deletions(-)
 create mode 100644 sample/C/mixed_external_and_libc_functions.c

diff --git a/lib/caotral/linker/builder.rb b/lib/caotral/linker/builder.rb
index f0e3d4e..c5c3e3c 100644
--- a/lib/caotral/linker/builder.rb
+++ b/lib/caotral/linker/builder.rb
@@ -291,6 +291,9 @@ def build
 
         old_syms = symtab_section.body.dup
         symtab_section.body.sort_by! { |sym| sym.info >> 4 }
+        sym_indexes = {}
+        symtab_section.body.each_with_index { |sym, index| sym_indexes[sym.object_id] = index }
+        sym_index_map = old_syms.each_with_index.to_h { |sym, index| [index, sym_indexes[sym.object_id]] }
         local_count = symtab_section.body.count { |sym| (sym.info >> 4) == SYMTAB_BIND[:locals] }
 
         symtab_section.header.set!(
@@ -366,13 +369,6 @@ def build
           end
         end
 
-        resolved_index = {}
-        symtab_section.body.each_with_index do |sym, index|
-          name = sym.name_string
-          next if name.empty? || sym.shndx == 0 || sym.bind != 1
-          resolved_index[name] ||= index
-        end
-
         sym_by_elf.each do |elf_obj, syms|
           syms.each do |sym|
             next if sym.shndx == 0
@@ -388,6 +384,17 @@ def build
           defined_global_index[sym.name_string] ||= index
         end
 
+        got_plt_offsets = got_plt_offsets.each_with_object({}) do |(old_index, offset), offsets|
+          new_index = sym_index_map[old_index]
+          offsets[new_index] = offset unless new_index.nil?
+        end
+
+        rela_plt_section.body.each do |rel|
+          new_index = sym_index_map[rel.sym]
+          next if new_index.nil?
+          rel.set!(info: (new_index << 32) | rel.type)
+        end
+
         rel_sections.each do |rel_section|
           rel_section.body.each do |rel|
             orig_sym = old_syms[rel.sym]
@@ -396,7 +403,7 @@ def build
             new_index = if orig_sym.shndx == 0 && defined_global_index.key?(name)
                           defined_global_index[orig_sym.name_string]
                         else
-                          resolved_index[name]
+                          sym_index_map[rel.sym]
                         end
             next if new_index.nil?
             rel.set!(info: (new_index << 32) | rel.type)
diff --git a/sample/C/mixed_external_and_libc_functions.c b/sample/C/mixed_external_and_libc_functions.c
new file mode 100644
index 0000000..1b61378
--- /dev/null
+++ b/sample/C/mixed_external_and_libc_functions.c
@@ -0,0 +1,7 @@
+extern int value_from_b(void);
+extern int puts(const char *);
+
+int main(void) {
+  puts("hello, glibc");
+  return value_from_b();
+}
diff --git a/test/caotral/linker/symbol_remap_test.rb b/test/caotral/linker/symbol_remap_test.rb
index 7d232d0..981ec3a 100644
--- a/test/caotral/linker/symbol_remap_test.rb
+++ b/test/caotral/linker/symbol_remap_test.rb
@@ -28,4 +28,23 @@ def test_remap_external_symbols
     ec, hc = check_process(status.to_i)
     assert_equal(ec, 42)
   end
+
+  def test_remap_external_symbols_using_glibc
+    inputs = ["mixed_external_and_libc_functions.o", "symbol_remap_external_b.o"]
+    files = inputs.map { |f| "sample/C/#{f.sub(/\.o$/, ".c")}" }
+    execute = "combined_with_glibc"
+    @generated = [execute] + inputs
+    inputs.zip(files).each { |o, i| IO.popen(["gcc", "-fPIC", "-c", "-o", o, "%s" % i]).close }
+    Caotral::Linker.link!(inputs:, output: execute, linker: "self", pie: true, needed: ["libc.so.6"])
+    elf = Caotral::Binary::ELF::Reader.read!(input: execute)
+    dynsym = elf.find_by_name(".dynsym")
+    dynsym_names = dynsym.body.map(&:name_string)
+    assert_equal(4, dynsym.body.size)
+    assert_include(dynsym_names, "main")
+    assert_include(dynsym_names, "value_from_b")
+    assert_include(dynsym_names, "puts")
+    _o, _e, status = Open3.capture3("./#{execute}")
+    ec, hc = check_process(status.to_i)
+    assert_equal(ec, 42)
+  end
 end