example
~/test/asm_linker/linker
1. Source code¶
main.c¶
C++
int add(int a, int b);
int main() {
int a = 10, b = 11;
printf("result: %d\n", add(a, b));
return 0;
}
foo.c¶
2. Command¶
Bash
clang foo.c -S -o foo.s
clang main.c -S -o main.s
clang foo.s main.s -o a.out
clang foo.c -c -o foo.o
clang main.c -c -o main.o
clang main.c foo.c -o a.out
Bash
clang main.c foo.c -o a.out -V
clang version 12.0.0 (https://github.com/llvm/llvm-project.git 154860af338f7b0c82cb04e91d6f199aa72cfdff)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/ken/workspace/llvm/build/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Candidate multilib: .;@m64
Selected multilib: .;@m64
"/home/ken/workspace/llvm/build/bin/clang-12" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -main-file-name main.c -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /home/ken/workspace/llvm/build/lib/clang/12.0.0 -internal-isystem /usr/local/include -internal-isystem /home/ken/workspace/llvm/build/lib/clang/12.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdebug-compilation-dir /home/ken/test/asm_linker/linker -ferror-limit 19 -fgnuc-version=4.2.1 -faddrsig -o /tmp/main-a6666a.o -x c main.c
clang -cc1 version 12.0.0 based upon LLVM 12.0.0git default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/home/ken/workspace/llvm/build/lib/clang/12.0.0/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
"/home/ken/workspace/llvm/build/bin/clang-12" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -main-file-name foo.c -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /home/ken/workspace/llvm/build/lib/clang/12.0.0 -internal-isystem /usr/local/include -internal-isystem /home/ken/workspace/llvm/build/lib/clang/12.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdebug-compilation-dir /home/ken/test/asm_linker/linker -ferror-limit 19 -fgnuc-version=4.2.1 -faddrsig -o /tmp/foo-51c971.o -x c foo.c
clang -cc1 version 12.0.0 based upon LLVM 12.0.0git default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/home/ken/workspace/llvm/build/lib/clang/12.0.0/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
"/usr/bin/ld" -z relro --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crt1.o /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/9/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/9 -L/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/9/../../../../lib64 -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib64 -L/usr/lib/x86_64-linux-gnu/../../lib64 -L/usr/lib/gcc/x86_64-linux-gnu/9/../../.. -L/home/ken/workspace/llvm/build/bin/../lib -L/lib -L/usr/lib /tmp/main-a6666a.o /tmp/foo-51c971.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-linux-gnu/9/crtend.o /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o
3. asm¶
foo.s¶
Bash
.text
.file "foo.c"
.globl add # -- Begin function add
.p2align 4, 0x90
.type add,@function
add: # @add
.cfi_startproc
# %bb.0: # %entry
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
movl %edi, -4(%rbp)
movl %esi, -8(%rbp)
movl -4(%rbp), %eax
addl -8(%rbp), %eax
popq %rbp
.cfi_def_cfa %rsp, 8
retq
.Lfunc_end0:
.size add, .Lfunc_end0-add
.cfi_endproc
# -- End function
.ident "clang version 12.0.0 (https://github.com/llvm/llvm-project.git 154860af338f7b0c82cb04e91d6f199aa72cfdff)"
.section ".note.GNU-stack","",@progbits
.addrsig
main.s¶
Bash
.text
.file "main.c"
.globl main # -- Begin function main
.p2align 4, 0x90
.type main,@function
main: # @main
.cfi_startproc
# %bb.0: # %entry
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
subq $16, %rsp
movl $0, -4(%rbp)
movl $10, -8(%rbp)
movl $11, -12(%rbp)
movl -8(%rbp), %edi // 将参数放到指令的位置
movl -12(%rbp), %esi
callq add // 调用foo.s中的add函数
movabsq $.L.str, %rdi
movl %eax, %esi
movb $0, %al
callq printf // 调用printf函数
xorl %ecx, %ecx
movl %eax, -16(%rbp) # 4-byte Spill
movl %ecx, %eax
addq $16, %rsp
popq %rbp
.cfi_def_cfa %rsp, 8
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
# -- End function
.type .L.str,@object # @.str
.section .rodata.str1.1,"aMS",@progbits,1
.L.str:
.asciz "result: %d\n"
.size .L.str, 12
.ident "clang version 12.0.0 (https://github.com/llvm/llvm-project.git 154860af338f7b0c82cb04e91d6f199aa72cfdff)"
.section ".note.GNU-stack","",@progbits
.addrsig
.addrsig_sym printf
.addrsig_sym add
4. linker¶
用多个.o文件和库文件组装成可执行文件。
a.dis¶
Bash
110 0000000000401130 <main>:
111 401130: 55 push %rbp
112 401131: 48 89 e5 mov %rsp,%rbp
113 401134: 48 83 ec 10 sub $0x10,%rsp
114 401138: c7 45 fc 00 00 00 00 movl $0x0,-0x4(%rbp)
115 40113f: c7 45 f8 0a 00 00 00 movl $0xa,-0x8(%rbp)
116 401146: c7 45 f4 0b 00 00 00 movl $0xb,-0xc(%rbp)
117 40114d: 8b 7d f8 mov -0x8(%rbp),%edi
118 401150: 8b 75 f4 mov -0xc(%rbp),%esi
119 401153: e8 28 00 00 00 callq 401180 <add> // add函数
120 401158: 48 bf 04 20 40 00 00 movabs $0x402004,%rdi
121 40115f: 00 00 00
122 401162: 89 c6 mov %eax,%esi
123 401164: b0 00 mov $0x0,%al
124 401166: e8 c5 fe ff ff callq 401030 <printf@plt> // 动态库中的printf函数
125 40116b: 31 c9 xor %ecx,%ecx
126 40116d: 89 45 f0 mov %eax,-0x10(%rbp)
127 401170: 89 c8 mov %ecx,%eax
128 401172: 48 83 c4 10 add $0x10,%rsp
129 401176: 5d pop %rbp
130 401177: c3 retq
131 401178: 0f 1f 84 00 00 00 00 nopl 0x0(%rax,%rax,1)
132 40117f: 00
133
134 0000000000401180 <add>:
135 401180: 55 push %rbp
136 401181: 48 89 e5 mov %rsp,%rbp
137 401184: 89 7d fc mov %edi,-0x4(%rbp)
138 401187: 89 75 f8 mov %esi,-0x8(%rbp)
139 40118a: 8b 45 fc mov -0x4(%rbp),%eax
140 40118d: 03 45 f8 add -0x8(%rbp),%eax
141 401190: 5d pop %rbp
142 401191: c3 r etq
143 401192: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
144 401199: 00 00 00
145 40119c: 0f 1f 40 00 nopl 0x0(%rax)
...
24 0000000000401030 <printf@plt>: // GLIBC中的printf函数
25 401030: ff 25 e2 2f 00 00 jmpq *0x2fe2(%rip) # 404018 <printf@GLIBC_2.2.5>
26 401036: 68 00 00 00 00 pushq $0x0
27 40103b: e9 e0 ff ff ff jmpq 401020 <.plt>
链接脚本文件¶
Bash
ld --verbose
GNU ld (GNU Binutils for Ubuntu) 2.34
Supported emulations:
elf_x86_64
elf32_x86_64
elf_i386
elf_iamcu
elf_l1om
elf_k1om
i386pep
i386pe
using internal linker script:
==================================================
/* Script for -z combreloc -z separate-code */
/* Copyright (C) 2014-2020 Free Software Foundation, Inc.
Copying and distribution of this script, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. */
OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64",
"elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(_start)
SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib");
SECTIONS
{
PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000)); . = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;
.interp : { *(.interp) }
.note.gnu.build-id : { *(.note.gnu.build-id) }
.hash : { *(.hash) }
.gnu.hash : { *(.gnu.hash) }
.dynsym : { *(.dynsym) }
.dynstr : { *(.dynstr) }
.gnu.version : { *(.gnu.version) }
.gnu.version_d : { *(.gnu.version_d) }
.gnu.version_r : { *(.gnu.version_r) }
.rela.dyn :
{
*(.rela.init)
*(.rela.text .rela.text.* .rela.gnu.linkonce.t.*)
*(.rela.fini)
*(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*)
*(.rela.data .rela.data.* .rela.gnu.linkonce.d.*)
*(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*)
*(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*)
*(.rela.ctors)
*(.rela.dtors)
*(.rela.got)
*(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*)
*(.rela.ldata .rela.ldata.* .rela.gnu.linkonce.l.*)
*(.rela.lbss .rela.lbss.* .rela.gnu.linkonce.lb.*)
*(.rela.lrodata .rela.lrodata.* .rela.gnu.linkonce.lr.*)
*(.rela.ifunc)
}
.rela.plt :
{
*(.rela.plt)
PROVIDE_HIDDEN (__rela_iplt_start = .);
*(.rela.iplt)
PROVIDE_HIDDEN (__rela_iplt_end = .);
}
. = ALIGN(CONSTANT (MAXPAGESIZE));
.init :
{
KEEP (*(SORT_NONE(.init)))
}
.plt : { *(.plt) *(.iplt) }
.plt.got : { *(.plt.got) }
.plt.sec : { *(.plt.sec) }
.text :
{
*(.text.unlikely .text.*_unlikely .text.unlikely.*)
*(.text.exit .text.exit.*)
*(.text.startup .text.startup.*)
*(.text.hot .text.hot.*)
*(SORT(.text.sorted.*))
*(.text .stub .text.* .gnu.linkonce.t.*)
/* .gnu.warning sections are handled specially by elf.em. */
*(.gnu.warning)
}
.fini :
{
KEEP (*(SORT_NONE(.fini)))
}
PROVIDE (__etext = .);
PROVIDE (_etext = .);
PROVIDE (etext = .);
. = ALIGN(CONSTANT (MAXPAGESIZE));
/* Adjust the address for the rodata segment. We want to adjust up to
the same address within the page on the next page up. */
. = SEGMENT_START("rodata-segment", ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)));
.rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
.rodata1 : { *(.rodata1) }
.eh_frame_hdr : { *(.eh_frame_hdr) *(.eh_frame_entry .eh_frame_entry.*) }
.eh_frame : ONLY_IF_RO { KEEP (*(.eh_frame)) *(.eh_frame.*) }
.gcc_except_table : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
.gnu_extab : ONLY_IF_RO { *(.gnu_extab*) }
/* These sections are generated by the Sun/Oracle C++ compiler. */
.exception_ranges : ONLY_IF_RO { *(.exception_ranges*) }
/* Adjust the address for the data segment. We want to adjust up to
the same address within the page on the next page up. */
. = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE));
/* Exception handling */
.eh_frame : ONLY_IF_RW { KEEP (*(.eh_frame)) *(.eh_frame.*) }
.gnu_extab : ONLY_IF_RW { *(.gnu_extab) }
.gcc_except_table : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) }
.exception_ranges : ONLY_IF_RW { *(.exception_ranges*) }
/* Thread Local Storage sections */
.tdata :
{
PROVIDE_HIDDEN (__tdata_start = .);
*(.tdata .tdata.* .gnu.linkonce.td.*)
}
.tbss : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
.preinit_array :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array))
PROVIDE_HIDDEN (__preinit_array_end = .);
}
.init_array :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))
PROVIDE_HIDDEN (__init_array_end = .);
}
.fini_array :
{
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))
KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors))
PROVIDE_HIDDEN (__fini_array_end = .);
}
.ctors :
{
/* gcc uses crtbegin.o to find the start of
the constructors, so we make sure it is
first. Because this is a wildcard, it
doesn't matter if the user does not
actually link against crtbegin.o; the
linker won't look for a file to match a
wildcard. The wildcard also means that it
doesn't matter which directory crtbegin.o
is in. */
KEEP (*crtbegin.o(.ctors))
KEEP (*crtbegin?.o(.ctors))
/* We don't want to include the .ctor section from
the crtend.o file until after the sorted ctors.
The .ctor section from the crtend file contains the
end of ctors marker and it must be last */
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
}
.dtors :
{
KEEP (*crtbegin.o(.dtors))
KEEP (*crtbegin?.o(.dtors))
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
KEEP (*(SORT(.dtors.*)))
KEEP (*(.dtors))
}
.jcr : { KEEP (*(.jcr)) }
.data.rel.ro : { *(.data.rel.ro.local* .gnu.linkonce.d.rel.ro.local.*) *(.data.rel.ro .data.rel.ro.* .gnu.linkonce.d.rel.ro.*) }
.dynamic : { *(.dynamic) }
.got : { *(.got) *(.igot) }
. = DATA_SEGMENT_RELRO_END (SIZEOF (.got.plt) >= 24 ? 24 : 0, .);
.got.plt : { *(.got.plt) *(.igot.plt) }
.data :
{
*(.data .data.* .gnu.linkonce.d.*)
SORT(CONSTRUCTORS)
}
.data1 : { *(.data1) }
_edata = .; PROVIDE (edata = .);
. = .;
__bss_start = .;
.bss :
{
*(.dynbss)
*(.bss .bss.* .gnu.linkonce.b.*)
*(COMMON)
/* Align here to ensure that the .bss section occupies space up to
_end. Align after .bss to ensure correct alignment even if the
.bss section disappears because there are no input sections.
FIXME: Why do we need it? When there is no .bss section, we do not
pad the .data section. */
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
.lbss :
{
*(.dynlbss)
*(.lbss .lbss.* .gnu.linkonce.lb.*)
*(LARGE_COMMON)
}
. = ALIGN(64 / 8);
. = SEGMENT_START("ldata-segment", .);
.lrodata ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
{
*(.lrodata .lrodata.* .gnu.linkonce.lr.*)
}
.ldata ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
{
*(.ldata .ldata.* .gnu.linkonce.l.*)
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
. = ALIGN(64 / 8);
_end = .; PROVIDE (end = .);
. = DATA_SEGMENT_END (.);
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
.gnu.build.attributes : { *(.gnu.build.attributes .gnu.build.attributes.*) }
/* DWARF debug sections.
Symbols in the DWARF debugging sections are relative to the beginning
of the section so we begin them at 0. */
/* DWARF 1 */
.debug 0 : { *(.debug) }
.line 0 : { *(.line) }
/* GNU DWARF 1 extensions */
.debug_srcinfo 0 : { *(.debug_srcinfo) }
.debug_sfnames 0 : { *(.debug_sfnames) }
/* DWARF 1.1 and DWARF 2 */
.debug_aranges 0 : { *(.debug_aranges) }
.debug_pubnames 0 : { *(.debug_pubnames) }
/* DWARF 2 */
.debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) }
.debug_abbrev 0 : { *(.debug_abbrev) }
.debug_line 0 : { *(.debug_line .debug_line.* .debug_line_end) }
.debug_frame 0 : { *(.debug_frame) }
.debug_str 0 : { *(.debug_str) }
.debug_loc 0 : { *(.debug_loc) }
.debug_macinfo 0 : { *(.debug_macinfo) }
/* SGI/MIPS DWARF 2 extensions */
.debug_weaknames 0 : { *(.debug_weaknames) }
.debug_funcnames 0 : { *(.debug_funcnames) }
.debug_typenames 0 : { *(.debug_typenames) }
.debug_varnames 0 : { *(.debug_varnames) }
/* DWARF 3 */
.debug_pubtypes 0 : { *(.debug_pubtypes) }
.debug_ranges 0 : { *(.debug_ranges) }
/* DWARF Extension. */
.debug_macro 0 : { *(.debug_macro) }
.debug_addr 0 : { *(.debug_addr) }
.gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
/DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) }
}
==================================================