For glibc with: From ac187dc4abde9ca6504c646106e2a7f7b2806262 Mon Sep 17 00:00:00 2001 From: H.J. Lu <hjl.tools@gmail.com> Date: Thu, 9 Jun 2016 04:43:16 -0700 Subject: [PATCH] Always indirect branch to __libc_start_main via GOT Since __libc_start_main in libc.so is called very early, lazy binding isn't relevant. Always call __libc_start_main with indirect branch via GOT to avoid extra branch to PLT slot. In case of static executable, ld in binutils 2.26 or above can convert indirect branch into direct branch: 0000000000400a80 <_start>: 400a80: 31 ed xor %ebp,%ebp 400a82: 49 89 d1 mov %rdx,%r9 400a85: 5e pop %rsi 400a86: 48 89 e2 mov %rsp,%rdx 400a89: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 400a8d: 50 push %rax 400a8e: 54 push %rsp 400a8f: 49 c7 c0 20 1b 40 00 mov $0x401b20,%r8 400a96: 48 c7 c1 90 1a 40 00 mov $0x401a90,%rcx 400a9d: 48 c7 c7 c0 03 40 00 mov $0x4003c0,%rdi 400aa4: 67 e8 96 09 00 00 addr32 callq 401440 <__libc_start_main> 400aaa: f4 hlt * sysdeps/x86_64/start.S (_start): Always indirect branch to __libc_start_main via GOT. I got (gdb) r Starting program: /export/build/gnu/binutils-gold/build-x86_64-linux/gold/testsuite/script_test_2 Missing separate debuginfos, use: dnf debuginfo-install glibc-2.22-17.1.fc23.x86_64 Program received signal SIGSEGV, Segmentation fault. 0x0000000000000000 in ?? () (gdb) bt #0 0x0000000000000000 in ?? () #1 0x000000001000002a in _start () (gdb) disass _start Dump of assembler code for function _start: 0x0000000010000000 <+0>: xor %ebp,%ebp 0x0000000010000002 <+2>: mov %rdx,%r9 0x0000000010000005 <+5>: pop %rsi 0x0000000010000006 <+6>: mov %rsp,%rdx 0x0000000010000009 <+9>: and $0xfffffffffffffff0,%rsp 0x000000001000000d <+13>: push %rax 0x000000001000000e <+14>: push %rsp 0x000000001000000f <+15>: mov $0x10000170,%r8 0x0000000010000016 <+22>: mov $0x10000100,%rcx 0x000000001000001d <+29>: mov $0x100001a0,%rdi 0x0000000010000024 <+36>: callq *0x100ee6(%rip) # 0x10100f10 <_DYNAMIC+496> ^^^^^^^^^^^ GOT offset is wrong It should be 0x10100f50. 0x000000001000002a <+42>: hlt End of assembler dump. (gdb) There are 44 section headers, starting at offset 0x3af8: Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ 0] NULL 0000000000000000 000000 000000 00 0 0 0 [ 1] .text PROGBITS 0000000010000000 001000 000172 00 AX 0 0 16 [ 2] .init PROGBITS 0000000010000174 001174 000017 00 AX 0 0 4 [ 3] .fini PROGBITS 000000001000018c 00118c 000009 00 AX 0 0 4 [ 4] .text.unlikely PROGBITS 0000000010000195 001195 000000 00 AX 0 0 1 [ 5] .text.startup PROGBITS 00000000100001a0 0011a0 0002dd 00 AX 0 0 16 [ 6] .plt PROGBITS 0000000010000480 001480 000040 10 AX 0 0 16 [ 7] .rela.plt RELA 00000000100004c0 0014c0 000048 18 AI 15 6 8 [ 8] .rela.dyn RELA 0000000010000508 001508 000030 18 A 15 0 8 [ 9] .rodata.cst4 PROGBITS 0000000010000538 001538 000004 04 AM 0 0 4 [10] .eh_frame PROGBITS 0000000010000540 001540 0000f4 00 A 0 0 8 [11] .eh_frame_hdr PROGBITS 0000000010000634 001634 000034 00 A 0 0 4 [12] .rodata PROGBITS 0000000010000670 001670 000056 00 A 0 0 16 [13] .rodata.str1.8 PROGBITS 00000000100006c8 0016c8 000287 01 AMS 0 0 8 [14] .rodata.str1.1 PROGBITS 000000001000094f 00194f 0000af 01 AMS 0 0 1 [15] .dynsym DYNSYM 0000000010000a00 001a00 0000c0 18 A 16 1 8 [16] .dynstr STRTAB 0000000010000ac0 001ac0 0000ae 00 A 0 0 1 [17] .gnu.hash GNU_HASH 0000000010000b70 001b70 00001c 00 A 15 0 8 [18] .interp PROGBITS 0000000010000b8c 001b8c 00001c 00 A 0 0 1 [19] .gnu.version VERSYM 0000000010000ba8 001ba8 000010 02 A 15 0 2 [20] .gnu.version_r VERNEED 0000000010000bb8 001bb8 000020 00 A 16 1 4 [21] .note.ABI-tag NOTE 0000000010000bd8 001bd8 000020 00 A 0 0 4 [22] .note.gnu.build-id NOTE 0000000010000bf8 001bf8 000024 00 A 0 0 4 [23] .data PROGBITS 0000000010100d00 001d00 000004 00 WA 0 0 1 [24] .jcr PROGBITS 0000000010100d08 001d08 000008 00 WA 0 0 8 [25] .tm_clone_table PROGBITS 0000000010100d10 001d10 000000 00 WA 0 0 8 [26] .fini_array FINI_ARRAY 0000000010100d10 001d10 000008 00 WA 0 0 8 [27] .init_array INIT_ARRAY 0000000010100d18 001d18 000008 00 WA 0 0 8 [28] .dynamic DYNAMIC 0000000010100d20 001d20 000200 10 WA 16 0 8 [29] .got.plt PROGBITS 0000000010100f20 001f20 000030 00 WA 0 0 8 [30] .got PROGBITS 0000000010100f50 001f50 000010 00 WA 0 0 8 [31] .bss NOBITS 0000000010100f60 001f60 000001 00 WA 0 0 1 [32] .gold_test PROGBITS 0000000020000010 002010 000053 00 WA 0 0 32 [33] .comment PROGBITS 0000000000000000 002063 00002d 01 MS 0 0 1 [34] .debug_info PROGBITS 0000000000000000 002090 0007d0 00 0 0 1 [35] .debug_abbrev PROGBITS 0000000000000000 002860 0001f9 00 0 0 1 [36] .debug_aranges PROGBITS 0000000000000000 002a59 000070 00 0 0 1 [37] .debug_ranges PROGBITS 0000000000000000 002ac9 000080 00 0 0 1 [38] .debug_line PROGBITS 0000000000000000 002b49 0002c5 00 0 0 1 [39] .debug_str PROGBITS 0000000000000000 002e0e 000326 01 MS 0 0 1 [40] .note.gnu.gold-version NOTE 0000000000000000 003134 00001c 00 0 0 4 [41] .symtab SYMTAB 0000000000000000 003150 0004c8 18 42 24 8 [42] .strtab STRTAB 0000000000000000 003618 00030a 00 0 0 1 [43] .shstrtab STRTAB 0000000000000000 003922 0001d0 00 0 0 1 Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings), I (info), L (link order), O (extra OS processing required), G (group), T (TLS), C (compressed), x (unknown), o (OS specific), E (exclude), l (large), p (processor specific) Relocation section '.rela.plt' at offset 0x14c0 contains 3 entries: Offset Info Type Symbol's Value Symbol's Name + Addend 0000000010100f38 0000000100000007 R_X86_64_JUMP_SLOT 0000000000000000 __libc_start_main@GLIBC_2.2.5 + 0 0000000010100f40 0000000600000007 R_X86_64_JUMP_SLOT 0000000000000000 memcmp@GLIBC_2.2.5 + 0 0000000010100f48 0000000700000007 R_X86_64_JUMP_SLOT 0000000000000000 __assert_fail@GLIBC_2.2.5 + 0 Relocation section '.rela.dyn' at offset 0x1508 contains 2 entries: Offset Info Type Symbol's Value Symbol's Name + Addend 0000000010100f50 0000000100000006 R_X86_64_GLOB_DAT 0000000000000000 __libc_start_main@GLIBC_2.2.5 + 0 0000000010100f58 0000000200000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0 gnu-6:pts/33[6]>
The master branch has been updated by H.J. Lu <hjl@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=3328c04b103286c3422aed59b97595bbbd9bbef5 commit 3328c04b103286c3422aed59b97595bbbd9bbef5 Author: H.J. Lu <hjl.tools@gmail.com> Date: Mon Jun 13 11:14:57 2016 -0700 Add .got.plt to testsuite/script_test_2.t The .got.plt section must be placed right after the .got section. Otherwise, GOT offset will be wrong. PR gold/20246 * testsuite/script_test_2.t: Add .got.plt after .got.
Fixed