Changes to handle elf image bases / text link-at addresses (#21)

Figure out the text offset for elf files. When testing on a system that
did not use ASLR by default a user found addr2line being invoked with
the wrong addresses.

src/platform/common.hpp

@@ -250,6 +250,7 @@ static_assert(n_digits(10) == 2, "n_digits utility producing the wrong result");
 static_assert(n_digits(11) == 2, "n_digits utility producing the wrong result");
 static_assert(n_digits(1024) == 4, "n_digits utility producing the wrong result");
 
+// TODO: Re-evaluate use of off_t
 template<typename T, typename std::enable_if<std::is_pod<T>::value, int>::type = 0>
 T load_bytes(FILE* obj_file, off_t offset) {
     T object;

src/platform/elf.hpp

@@ -0,0 +1,87 @@
+#ifndef ELF_HPP
+#define ELF_HPP
+
+#include "common.hpp"
+
+#if IS_LINUX
+#include <array>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+
+#include <elf.h>
+
+template<typename T, typename std::enable_if<std::is_integral<T>::value, int>::type = 0>
+T elf_byteswap_if_needed(T value, bool elf_is_little) {
+    if(is_little_endian() == elf_is_little) {
+        return value;
+    } else {
+        return byteswap(value);
+    }
+}
+
+// TODO: Re-evaluate use of off_t
+// I think we can rely on PT_PHDR https://stackoverflow.com/q/61568612/15675011...
+static uintptr_t elf_get_module_image_base_from_program_table(
+    FILE* file,
+    bool is_64,
+    bool is_little_endian,
+    off_t e_phoff,
+    off_t e_phentsize,
+    int e_phnum
+) {
+    for(int i = 0; i < e_phnum; i++) {
+        if(is_64) {
+            Elf64_Phdr program_header = load_bytes<Elf64_Phdr>(file, e_phoff + e_phentsize * i);
+            if(elf_byteswap_if_needed(program_header.p_type, is_little_endian) == PT_PHDR) {
+                return elf_byteswap_if_needed(program_header.p_vaddr, is_little_endian)
+                        - elf_byteswap_if_needed(program_header.p_offset, is_little_endian);
+            }
+        } else {
+            Elf32_Phdr program_header = load_bytes<Elf32_Phdr>(file, e_phoff + e_phentsize * i);
+            if(elf_byteswap_if_needed(program_header.p_type, is_little_endian) == PT_PHDR) {
+                return elf_byteswap_if_needed(program_header.p_vaddr, is_little_endian)
+                        - elf_byteswap_if_needed(program_header.p_offset, is_little_endian);
+            }
+        }
+    }
+    return 0;
+}
+
+static uintptr_t elf_get_module_image_base(const std::string& obj_path) {
+    FILE* file = fopen(obj_path.c_str(), "rb");
+    // Initial checks/metadata
+    auto magic = load_bytes<std::array<char, 4>>(file, 0);
+    internal_verify(magic == (std::array<char, 4>{0x7F, 'E', 'L', 'F'}));
+    bool is_64 = load_bytes<uint8_t>(file, 4) == 2;
+    bool is_little_endian = load_bytes<uint8_t>(file, 5) == 1;
+    internal_verify(load_bytes<uint8_t>(file, 6) == 1, "Unexpected ELF version");
+    //
+    if(is_64) {
+        Elf64_Ehdr file_header = load_bytes<Elf64_Ehdr>(file, 0);
+        internal_verify(file_header.e_ehsize == sizeof(Elf64_Ehdr));
+        return elf_get_module_image_base_from_program_table(
+            file,
+            is_64,
+            is_little_endian,
+            elf_byteswap_if_needed(file_header.e_phoff, is_little_endian),
+            elf_byteswap_if_needed(file_header.e_phentsize, is_little_endian),
+            elf_byteswap_if_needed(file_header.e_phnum, is_little_endian)
+        );
+    } else {
+        Elf32_Ehdr file_header = load_bytes<Elf32_Ehdr>(file, 0);
+        internal_verify(file_header.e_ehsize == sizeof(Elf32_Ehdr));
+        return elf_get_module_image_base_from_program_table(
+            file,
+            is_64,
+            is_little_endian,
+            elf_byteswap_if_needed(file_header.e_phoff, is_little_endian),
+            elf_byteswap_if_needed(file_header.e_phentsize, is_little_endian),
+            elf_byteswap_if_needed(file_header.e_phnum, is_little_endian)
+        );
+    }
+}
+
+#endif
+
+#endif

src/platform/mach-o.hpp

@@ -1,13 +1,13 @@
 #ifndef MACHO_HPP
 #define MACHO_HPP
 
+#include "common.hpp"
+
 #if IS_APPLE
 #include <cstdio>
 #include <cstring>
 #include <type_traits>
 
-#include "common.hpp"
-
 #include <mach-o/loader.h>
 #include <mach-o/swap.h>
 #include <mach-o/fat.h>

src/platform/pe.hpp

@@ -1,15 +1,15 @@
 #ifndef PE_HPP
 #define PE_HPP
 
+#include "common.hpp"
+
+#if IS_WINDOWS
 #include <array>
 #include <cstddef>
 #include <cstdio>
 #include <cstring>
 #include <string>
 
-#include "common.hpp"
-
-#if IS_WINDOWS
 #include <windows.h>
 
 template<typename T, typename std::enable_if<std::is_integral<T>::value, int>::type = 0>

src/symbols/symbols_with_addr2line.cpp

@@ -21,6 +21,8 @@
  #include <sys/wait.h>
  #if IS_APPLE
   #include "../platform/mach-o.hpp"
+ #else
+  #include "../platform/elf.hpp"
  #endif
 #elif IS_WINDOWS
  #include "../platform/pe.hpp"
@@ -166,8 +168,7 @@ namespace cpptrace {
 
         #if !IS_APPLE
         uintptr_t get_module_image_base(const dlframe &entry) {
-            (void)entry;
-            return 0;
+            return elf_get_module_image_base(entry.obj_path);
         }
         #else
         uintptr_t get_module_image_base(const dlframe &entry) {