Strip libc.so before linking against it
[termux-packages] / packages / termux-elf-cleaner / termux-elf-cleaner.cpp
1 #include <algorithm>
2 #include <fcntl.h>
3 #include <stdio.h>
4 #include <stdlib.h>
5 #include <string.h>
6 #include <sys/mman.h>
7 #include <sys/stat.h>
8 #include <sys/types.h>
9 #include <unistd.h>
10
11 #ifdef __APPLE__
12 # include "elf.h"
13 #else
14 # include <elf.h>
15 #endif
16
17 #define DT_VERSYM 0x6ffffff0
18 #define DT_VERNEEDED 0x6ffffffe
19 #define DT_VERNEEDNUM 0x6fffffff
20
21 template<typename ElfHeaderType /*Elf{32,64}_Ehdr*/,
22 typename ElfSectionHeaderType /*Elf{32,64}_Shdr*/,
23 typename ElfDynamicSectionEntryType /* Elf{32,64}_Dyn */>
24 bool process_elf(uint8_t* bytes, size_t elf_file_size, char const* file_name)
25 {
26 if (sizeof(ElfSectionHeaderType) > elf_file_size) {
27 fprintf(stderr, "termux-elf-cleaner: Elf header for '%s' would end at %zu but file size only %zu\n", file_name, sizeof(ElfSectionHeaderType), elf_file_size);
28 return false;
29 }
30 ElfHeaderType* elf_hdr = reinterpret_cast<ElfHeaderType*>(bytes);
31
32 size_t last_section_header_byte = elf_hdr->e_shoff + sizeof(ElfSectionHeaderType) * elf_hdr->e_shnum;
33 if (last_section_header_byte > elf_file_size) {
34 fprintf(stderr, "termux-elf-cleaner: Section header for '%s' would end at %zu but file size only %zu\n", file_name, last_section_header_byte, elf_file_size);
35 return false;
36 }
37 ElfSectionHeaderType* section_header_table = reinterpret_cast<ElfSectionHeaderType*>(bytes + elf_hdr->e_shoff);
38
39 for (unsigned int i = 1; i < elf_hdr->e_shnum; i++) {
40 ElfSectionHeaderType* section_header_entry = section_header_table + i;
41 if (section_header_entry->sh_type == SHT_DYNAMIC) {
42 size_t const last_dynamic_section_byte = section_header_entry->sh_offset + section_header_entry->sh_size;
43 if (last_dynamic_section_byte > elf_file_size) {
44 fprintf(stderr, "termux-elf-cleaner: Dynamic section for '%s' would end at %zu but file size only %zu\n", file_name, last_dynamic_section_byte, elf_file_size);
45 return false;
46 }
47
48 size_t const dynamic_section_entries = section_header_entry->sh_size / sizeof(ElfDynamicSectionEntryType);
49 ElfDynamicSectionEntryType* const dynamic_section =
50 reinterpret_cast<ElfDynamicSectionEntryType*>(bytes + section_header_entry->sh_offset);
51
52 unsigned int last_nonnull_entry_idx = 0;
53 for (unsigned int j = dynamic_section_entries - 1; j > 0; j--) {
54 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
55 if (dynamic_section_entry->d_tag != DT_NULL) {
56 last_nonnull_entry_idx = j;
57 break;
58 }
59 }
60
61 for (unsigned int j = 0; j < dynamic_section_entries; j++) {
62 ElfDynamicSectionEntryType* dynamic_section_entry = dynamic_section + j;
63 char const* removed_name = nullptr;
64 switch (dynamic_section_entry->d_tag) {
65 case DT_VERSYM: removed_name = "DT_VERSYM"; break;
66 case DT_VERNEEDED: removed_name = "DT_VERNEEDED"; break;
67 case DT_VERNEEDNUM: removed_name = "DT_VERNEEDNUM"; break;
68 case DT_VERDEF: removed_name = "DT_VERDEF"; break;
69 case DT_VERDEFNUM: removed_name = "DT_VERDEFNUM"; break;
70 case DT_RPATH: removed_name = "DT_RPATH"; break;
71 case DT_RUNPATH: removed_name = "DT_RUNPATH"; break;
72 }
73 if (removed_name != nullptr) {
74 printf("termux-elf-cleaner: Removing the %s dynamic section entry from '%s'\n", removed_name, file_name);
75 // Tag the entry with DT_NULL and put it last:
76 dynamic_section_entry->d_tag = DT_NULL;
77 // Decrease j to process new entry index:
78 std::swap(dynamic_section[j--], dynamic_section[last_nonnull_entry_idx--]);
79 }
80 }
81 } else if (section_header_entry->sh_type == SHT_GNU_verdef ||
82 section_header_entry->sh_type == SHT_GNU_verneed ||
83 section_header_entry->sh_type == SHT_GNU_versym) {
84 printf("termux-elf-cleaner: Removing version section from '%s'\n", file_name);
85 section_header_entry->sh_type = SHN_UNDEF;
86 }
87 }
88 return true;
89 }
90
91
92 int main(int argc, char const** argv)
93 {
94 if (argc < 2 || (argc == 2 && strcmp(argv[1], "-h")==0)) {
95 fprintf(stderr, "usage: %s <filename>\n", argv[0]);
96 fprintf(stderr, " Processes ELF files to remove DT_VERNEEDED, DT_VERNEEDNUM, DT_RPATH\n"
97 " and DT_RUNPATH entries (which the Android linker warns about)\n");
98 return 1;
99 }
100
101 for (int i = 1; i < argc; i++) {
102 char const* file_name = argv[i];
103 int fd = open(file_name, O_RDWR);
104 if (fd < 0) {
105 char* error_message;
106 if (asprintf(&error_message, "open(\"%s\")", file_name) == -1) error_message = (char*) "open()";
107 perror(error_message);
108 return 1;
109 }
110
111 struct stat st;
112 if (fstat(fd, &st) < 0) { perror("fstat()"); return 1; }
113
114 if (st.st_size < (long long) sizeof(Elf32_Ehdr)) {
115 close(fd);
116 continue;
117 }
118
119 void* mem = mmap(0, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
120 if (mem == MAP_FAILED) { perror("mmap()"); return 1; }
121
122 uint8_t* bytes = reinterpret_cast<uint8_t*>(mem);
123 if (!(bytes[0] == 0x7F && bytes[1] == 'E' && bytes[2] == 'L' && bytes[3] == 'F')) {
124 // Not the ELF magic number.
125 munmap(mem, st.st_size);
126 close(fd);
127 continue;
128 }
129
130 if (bytes[/*EI_DATA*/5] != 1) {
131 fprintf(stderr, "termux-elf-cleaner: Not little endianness in '%s'\n", file_name);
132 munmap(mem, st.st_size);
133 close(fd);
134 continue;
135 }
136
137 uint8_t const bit_value = bytes[/*EI_CLASS*/4];
138 if (bit_value == 1) {
139 if (!process_elf<Elf32_Ehdr, Elf32_Shdr, Elf32_Dyn>(bytes, st.st_size, file_name)) return 1;
140 } else if (bit_value == 2) {
141 if (!process_elf<Elf64_Ehdr, Elf64_Shdr, Elf64_Dyn>(bytes, st.st_size, file_name)) return 1;
142 } else {
143 printf("termux-elf-cleaner: Incorrect bit value %d in '%s'\n", bit_value, file_name);
144 return 1;
145 }
146
147 if (msync(mem, st.st_size, MS_SYNC) < 0) { perror("msync()"); return 1; }
148
149 munmap(mem, st.st_size);
150 close(fd);
151 }
152 return 0;
153 }
154