linux编程──gcc和clang

实验链接

编译原理实验-GCC/Clang工具链在ARM架构上的使用

实验报告

第1关：理解程序的不同表示形式

##问题1-1：
如果在命令行下执行

gcc -DNEG -E sample.c -o sample.i

生成的sample.i 与之前的有何区别？
根据定义NEG,而选择了M定义为-4

##问题1-2
请对比sample-32.s和sample.s，找出它们的区别，并上网检索给出产生这些区别的原因。如：

• pushq和pushl
• rsp和esp
  sample-32.s和sample.s的区别

diff sample-32.s sample.s

1,4c1,6
<         .file   "sample.c"
<         .text
<         .globl  main
<         .type   main, @function
---
>       .arch armv8-a
>       .file   "sample.c"
>       .text
>       .align  2
>       .global main
>       .type   main, %function
6,18c8,17
< .LFB0:
<         .cfi_startproc
<         pushl   %ebp
<         .cfi_def_cfa_offset 8
<         .cfi_offset 5, -8
<         movl    %esp, %ebp
<         .cfi_def_cfa_register 5
<         subl    $16, %esp
<         movl    $4, -4(%ebp)
<         cmpl    $0, -4(%ebp)
<         je      .L2
<         addl    $4, -4(%ebp)
<         jmp     .L3
---
>       sub     sp, sp, #16
>       mov     w0, -4
>       str     w0, [sp, 12]
>       ldr     w0, [sp, 12]
>       cmp     w0, 0
>       beq     .L2
>       ldr     w0, [sp, 12]
>       add     w0, w0, 4
>       str     w0, [sp, 12]
>       b       .L3
20c19,21
<         sall    $2, -4(%ebp)
---
>       ldr     w0, [sp, 12]
>       lsl     w0, w0, 2
>       str     w0, [sp, 12]
22,31c23,28
<         movl    $0, %eax
<         leave
<         .cfi_restore 5
<         .cfi_def_cfa 4, 4
<         ret
<         .cfi_endproc
< .LFE0:
<         .size   main, .-main
<         .ident  "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
<         .section        .note.GNU-stack,"",@progbits
---
>       mov     w0, 0
>       add     sp, sp, 16
>       ret
>       .size   main, .-main
>       .ident  "GCC: (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
>       .section        .note.GNU-stack,"",@progbits

问题1-3 你可以用clang替换gcc，重复上面的各步，比较使用clang和gcc分别输出的结果有何异同。

gcc sample.c -o sample -v
clang sample.c -o sample -v

diff gcc.txt clang.txt 
1,5c1,2
< Using built-in specs.
< COLLECT_GCC=gcc
< COLLECT_LTO_WRAPPER=/usr/lib/gcc/aarch64-linux-gnu/5/lto-wrapper
< Target: aarch64-linux-gnu
< Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libquadmath --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-arm64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-arm64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-arm64 --with-arch-directory=aarch64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-multiarch --enable-fix-cortex-a53-843419 --disable-werror --enable-checking=release --build=aarch64-linux-gnu --host=aarch64-linux-gnu --target=aarch64-linux-gnu
---
> clang version 10.0.1 
> Target: aarch64-unknown-linux-gnu
7,14c4,14
< gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12) 
< COLLECT_GCC_OPTIONS='-o' 'sample' '-v' '-mlittle-endian' '-mabi=lp64'
<  /usr/lib/gcc/aarch64-linux-gnu/5/cc1 -quiet -v -imultiarch aarch64-linux-gnu sample.c -quiet -dumpbase sample.c -mlittle-endian -mabi=lp64 -auxbase sample -version -fstack-protector-strong -Wformat -Wformat-security -o /tmp/cc1Kcmw6.s
< GNU C11 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12) version 5.4.0 20160609 (aarch64-linux-gnu)
<         compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3
< GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
< ignoring nonexistent directory "/usr/local/include/aarch64-linux-gnu"
< ignoring nonexistent directory "/usr/lib/gcc/aarch64-linux-gnu/5/../../../../aarch64-linux-gnu/include"
---
> InstalledDir: /opt/llvm10/llvm-install/bin
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/5
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/5.4.0
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/6.0.0
> Selected GCC installation: /usr/lib/gcc/aarch64-linux-gnu/5.4.0
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
>  "/opt/llvm10/llvm-install/bin/clang-10" -cc1 -triple aarch64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name sample.c -mrelocation-model static -mthread-model posix -mframe-pointer=non-leaf -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -target-cpu generic -target-feature +neon -target-abi aapcs -fallow-half-arguments-and-returns -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /opt/llvm10/llvm-install/lib/clang/10.0.1 -internal-isystem /usr/local/include -internal-isystem /opt/llvm10/llvm-install/lib/clang/10.0.1/include -internal-externc-isystem /usr/include/aarch64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdebug-compilation-dir /data/workspace/myshixun -ferror-limit 19 -fmessage-length 0 -fno-signed-char -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o /tmp/sample-ee930b.o -x c sample.c
> clang -cc1 version 10.0.1 based upon LLVM 10.0.1 default target aarch64-unknown-linux-gnu
> ignoring nonexistent directory "/include"
17d16
<  /usr/lib/gcc/aarch64-linux-gnu/5/include
19c18
<  /usr/lib/gcc/aarch64-linux-gnu/5/include-fixed
---
>  /opt/llvm10/llvm-install/lib/clang/10.0.1/include
23,33c22
< GNU C11 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12) version 5.4.0 20160609 (aarch64-linux-gnu)
<         compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3
< GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
< Compiler executable checksum: 0aba823f581e395c09d29a3a6f3b731f
< COLLECT_GCC_OPTIONS='-o' 'sample' '-v' '-mlittle-endian' '-mabi=lp64'
<  as -v -EL -mabi=lp64 -o /tmp/cc281Jv1.o /tmp/cc1Kcmw6.s
< GNU assembler version 2.26.1 (aarch64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.26.1
< COMPILER_PATH=/usr/lib/gcc/aarch64-linux-gnu/5/:/usr/lib/gcc/aarch64-linux-gnu/5/:/usr/lib/gcc/aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/5/:/usr/lib/gcc/aarch64-linux-gnu/
< LIBRARY_PATH=/usr/lib/gcc/aarch64-linux-gnu/5/:/usr/lib/gcc/aarch64-linux-gnu/5/../../../aarch64-linux-gnu/:/usr/lib/gcc/aarch64-linux-gnu/5/../../../../lib/:/lib/aarch64-linux-gnu/:/lib/../lib/:/usr/lib/aarch64-linux-gnu/:/usr/lib/../lib/:/opt/llvm10/antlr4-cpp/dist/:/opt/llvm10/antlr4-cpp/dist/:./:/usr/lib/gcc/aarch64-linux-gnu/5/../../../:/lib/:/usr/lib/
< COLLECT_GCC_OPTIONS='-o' 'sample' '-v' '-mlittle-endian' '-mabi=lp64'
<  /usr/lib/gcc/aarch64-linux-gnu/5/collect2 -plugin /usr/lib/gcc/aarch64-linux-gnu/5/liblto_plugin.so -plugin-opt=/usr/lib/gcc/aarch64-linux-gnu/5/lto-wrapper -plugin-opt=-fresolution=/tmp/ccjhDePW.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --sysroot=/ --build-id --eh-frame-hdr --hash-style=gnu --as-needed -dynamic-linker /lib/ld-linux-aarch64.so.1 -X -EL -maarch64linux --fix-cortex-a53-843419 -z relro -o sample /usr/lib/gcc/aarch64-linux-gnu/5/../../../aarch64-linux-gnu/crt1.o /usr/lib/gcc/aarch64-linux-gnu/5/../../../aarch64-linux-gnu/crti.o /usr/lib/gcc/aarch64-linux-gnu/5/crtbegin.o -L/usr/lib/gcc/aarch64-linux-gnu/5 -L/usr/lib/gcc/aarch64-linux-gnu/5/../../../aarch64-linux-gnu -L/usr/lib/gcc/aarch64-linux-gnu/5/../../../../lib -L/lib/aarch64-linux-gnu -L/lib/../lib -L/usr/lib/aarch64-linux-gnu -L/usr/lib/../lib -L/opt/llvm10/antlr4-cpp/dist -L/opt/llvm10/antlr4-cpp/dist -L. -L/usr/lib/gcc/aarch64-linux-gnu/5/../../.. /tmp/cc281Jv1.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/aarch64-linux-gnu/5/crtend.o /usr/lib/gcc/aarch64-linux-gnu/5/../../../aarch64-linux-gnu/crtn.o
---
>  "/usr/bin/ld" -EL -z relro --hash-style=gnu --eh-frame-hdr -m aarch64linux -dynamic-linker /lib/ld-linux-aarch64.so.1 -o sample /usr/lib/gcc/aarch64-linux-gnu/5.4.0/../../../aarch64-linux-gnu/crt1.o /usr/lib/gcc/aarch64-linux-gnu/5.4.0/../../../aarch64-linux-gnu/crti.o /usr/lib/gcc/aarch64-linux-gnu/5.4.0/crtbegin.o -L/usr/lib/gcc/aarch64-linux-gnu/5.4.0 -L/usr/lib/gcc/aarch64-linux-gnu/5.4.0/../../../aarch64-linux-gnu -L/lib/aarch64-linux-gnu -L/usr/lib/aarch64-linux-gnu -L/usr/lib/gcc/aarch64-linux-gnu/5.4.0/../../.. -L/opt/llvm10/llvm-install/bin/../lib -L/lib -L/usr/lib -L/opt/llvm10/antlr4-cpp/dist -L/opt/llvm10/antlr4-cpp/dist -L. /tmp/sample-ee930b.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/aarch64-linux-gnu/5.4.0/crtend.o /usr/lib/gcc/aarch64-linux-gnu/5.4.0/../../../aarch64-linux-gnu/crtn.o

第2关：理解使用库的C程序的编译和链接

问题2-1：

-nostdinc选项的用处是什么？
请列出 EduCoder 平台上 gcc C程序默认的头文件查找路径
如何在使用了-nostdinc选项的同时使得上述命令编译通过? 请进一步说明通过的原因（不能修改源文件）。

命令选项 -nostdinc 不搜索默认路径头文件
-nostdinc: 不要在标准系统目录中寻找文件，只是搜索‘-I’选项指定的目录

root@evassh-17600448:/data/workspace/myshixun/lab2# gcc -E sample-io.c -o sample-io.i
root@evassh-17600448:/data/workspace/myshixun/lab2# gcc sample-io.i -o sample-io
root@evassh-17600448:/data/workspace/myshixun/lab2# ./sample-io 
Hello, world!
a=8

第3关：C 程序的编写和编译以及各种程序表示的对比

在文件HW/H3/c/sort.c中编写一个排序程序

#include<stdio.h>
#define N 1001
void selectSort(int a[], int n);
int main(){int n;scanf("%d", &n);int a[N];for(int i=0;i<n;i++){scanf("%d", &a[i]);}selectSort(a, n);for(int i=0;i<n;i++){printf("%d ", a[i]);}printf("\n");return 0;
}
// 排序函数
void selectSort(int a[], int n)
{for(int i=0;i<n;i++){int k=i;for(int j=i+1;j<n;j++){if(a[j]<a[k]){k=j;}}if(k!=i){int t=a[k];a[k]=a[i];a[i]=t;}}
}

在文件HW/H3/c/Makefile中编写编译规则

exe=sort
$(exe):$(wildcard *.c)gcc -o $@ $^.PHONY:cleanclean:rm -f $(exe)echo "clean object files"