编译器工具链初步解析
GNU
一般编译器分为三个stage: cc1,as,ld.
- 预处理器：cc1
- 编译器：cc1 →输出汇编代码 (* .s)
- 汇编程序：as → 输出目标文件 (* .o)
- 链接器：ld (collect2 )→输出执行对象文件（a.out等） 在gcc版本 2 之前，预处理器是一个名为 cpp 的命令。cpp 是完成 C 语言源文件上的文件包含和宏置换，在预处理过程没有输出文件 .i 棒的扩展名作为过程的结果文件。从 gcc版本 3 开始，编译器cc1也用作预处理器。
从 collect2 调用链接器 ld。当实际删除 /usr/bin/ld 并运行 collect2 时，会收到类似 ld not found 的错误。
gcc放了-v 选项，gcc就可以看到处理的过程了。
root@node2:~/Downloads# gcc ./a.c -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 10.3.0-1ubuntu1~20.04' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-10 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-10-S4I5Pr/gcc-10-10.3.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-S4I5Pr/gcc-10-10.3.0/debian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-build-config=bootstrap-lto-lean --enable-link-mutex
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.3.0 (Ubuntu 10.3.0-1ubuntu1~20.04)
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/10/cc1 -quiet -v -imultiarch x86_64-linux-gnu ./a.c -quiet -dumpbase a.c -mtune=generic -march=x86-64 -auxbase a -version -fasynchronous-unwind-tables -fstack-protector-strong -Wformat -Wformat-security -fstack-clash-protection -fcf-protection -o /tmp/ccq3lrsa.s
GNU C17 (Ubuntu 10.3.0-1ubuntu1~20.04) version 10.3.0 (x86_64-linux-gnu)
compiled by GNU C version 10.3.0, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/include-fixed"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-linux-gnu/10/include
/usr/local/include
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C17 (Ubuntu 10.3.0-1ubuntu1~20.04) version 10.3.0 (x86_64-linux-gnu)
compiled by GNU C version 10.3.0, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: f2dc2f7bd2244142e4cf7a4d43b693bf
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
as -v --64 -o /tmp/ccRKbQ88.o /tmp/ccq3lrsa.s
GNU assembler version 2.34 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.34
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/10/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/10/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/10/collect2 -plugin /usr/lib/gcc/x86_64-linux-gnu/10/liblto_plugin.so -plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper -plugin-opt=-fresolution=/tmp/ccYzFpGa.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 --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -z now -z relro /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/Scrt1.o /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/10/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu/10 -L/usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib -L/lib/x86_64-linux-gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/10/../../.. /tmp/ccRKbQ88.o -lgcc --push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state --as-needed -lgcc_s --pop-state /usr/lib/gcc/x86_64-linux-gnu/10/crtendS.o /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
riscv-gnu-toolchain
LLVM的链接器只在linux上有完整实现，所以为了本编译器的跨平台测试，仍然使用LLVM编译.ll文件，gcc链接器后端。有关riscv链接器的dark side，详见MaskRay
LLVM
LLVM也有对应的一套工具链。对于 GCC，可以仅使用宿主 C++ 编译器（通常是 GCC）从 Binutils 和 GCC 源代码构建完整的 C/C++ 交叉编译器。Clang 依赖于 GCC，并且您无法仅使用 LLVM 项目的源代码构建完整的交叉编译器（因此您必须按原样使用 GCC 头文件和库）。这是因为CMake需要一个完整的C/C++编译器（可以生成a.out），除此之外，还需要在Clang本身上构建Clang的运行时库compiler-rt。如果使用 GCC 构建甚至一个库，该库将依赖于 GCC 头文件，因此所有其他库都必须使用相同的 GCC 构建。
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: x86_64-apple-darwin21.1.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
"/Library/Developer/CommandLineTools/usr/bin/clang" -cc1 -triple x86_64-apple-macosx12.0.0 -Wundef-prefix=TARGET_OS_ -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all --mrelax-relocations -disable-free -disable-llvm-verifier -discard-value-names -main-file-name a.c -mrelocation-model pic -pic-level 2 -mframe-pointer=all -fno-strict-return -fno-rounding-math -munwind-tables -target-sdk-version=12.1 -fvisibility-inlines-hidden-static-local-var -target-cpu penryn -tune-cpu generic -debugger-tuning=lldb -target-linker-version 711 -v -resource-dir /Library/Developer/CommandLineTools/usr/lib/clang/13.0.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -I/usr/local/include -internal-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include -internal-isystem /Library/Developer/CommandLineTools/usr/lib/clang/13.0.0/include -internal-externc-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -internal-externc-isystem /Library/Developer/CommandLineTools/usr/include -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -Wno-elaborated-enum-base -fdebug-compilation-dir /Users/yiweiyang/project/hpl-ai -ferror-limit 19 -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fmax-type-align=16 -fcommon -fcolor-diagnostics -clang-vendor-feature=+nullptrToBoolConversion -clang-vendor-feature=+messageToSelfInClassMethodIdReturnType -clang-vendor-feature=+disableInferNewAvailabilityFromInit -clang-vendor-feature=+disableNeonImmediateRangeCheck -clang-vendor-feature=+disableNonDependentMemberExprInCurrentInstantiation -fno-odr-hash-protocols -clang-vendor-feature=+revert09abecef7bbf -mllvm -disable-aligned-alloc-awareness=1 -mllvm -enable-dse-memoryssa=0 -o /var/folders/1x/tx5s6n452zv5qkyx4n3xz58c0000gn/T/a-d764d3.o -x c a.c
clang -cc1 version 13.0.0 (clang-1300.0.29.30) default target x86_64-apple-darwin21.1.0
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/local/include"
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/Library/Developer/CommandLineTools/usr/lib/clang/13.0.0/include
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include
/Library/Developer/CommandLineTools/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Library/Developer/CommandLineTools/usr/bin/ld" -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -platform_version macos 12.0.0 12.1 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -o a.out -L/usr/local/lib /var/folders/1x/tx5s6n452zv5qkyx4n3xz58c0000gn/T/a-d764d3.o -lSystem /Library/Developer/CommandLineTools/usr/lib/clang/13.0.0/lib/darwin/libclang_rt.osx.a
在不同的编译器之间需要考虑ABI兼容的问题。 相比之下
$A$prototype:
.word 4 # 0x4
.word 4 # 0x4
.word ($A$dispatchTable)
.word 42 # 0x2a
.size $A$prototype, 16
.type $A$dispatchTable,@object # @"$A$dispatchTable"
.section .sdata,"aw",@progbits
.globl $A$dispatchTable
.p2align 3
Venus
在体系结构课上使用的是Venus做模拟，使用的ecall遵循spim的规则，其call convention如下
| ID (a0) | Name | Description |
|---|---|---|
| 1 | print_int | prints integer in a1 |
| 4 | print_string | prints the null-terminated string whose address is in a1 |
| 9 | sbrk | allocates a1 bytes on the heap, returns pointer to start in a0 |
| 10 | exit | ends the program |
| 11 | print_character | prints ASCII character in a1 |
| 13 | openFile | Opens the file in the VFS where a pointer to the path is in a1 and the permission bits are in a2. Returns to a0 an integer representing the file descriptor. |
| 14 | readFile | Takes in: a1 = FileDescriptor, a2 = Where to store the data (an array), a3 = the amount you want to read from the file. Returns a0 = Number of items which were read and put to the given array. If it is less than a3 it is either an error or EOF. You will have to use another ecall to determine what was the cause. |
| 15 | writeFile | Takes in: a1 = FileDescriptor, a2 = Buffer to read data from, a3 = amount of the buffer you want to read, a4 = Size of each item. Returns a0 = Number of items written. If it is less than a3 it is either an error or EOF. You will have to use another ecall to determine what was the cause. Also, you need to flush or close the file for the changes to be written to the VFS. |
| 16 | closeFile | Takes in: a1 = FileDescriptor. Returns 0 on success and EOF (-1) otherwise. Will flush the data as well. |
| 17 | exit2 | ends the program with return code in a1 |
| 18 | fflush | Takes in: a1 = FileDescriptor. Will return 0 on success otherwise EOF on an error. |
| 19 | feof | Takes in: a1 = FileDescriptor. Returns a nonzero value when the end of file is reached otherwise, it returns 0. |
| 20 | ferror | Takes in: a1 = FileDescriptor. Returns Nnnzero value if the file stream has errors occurred, 0 otherwise. |
| 34 | printHex | prints hex in a1 |
| 0x3CC | vlib | Please check out the vlib page to see what functions you can use! |
以下是使用方法
li a0, 1 # syscall number for printing integer
li a1, 1024 # the integer we're printing
ecall # issue system call
a0为syscall参数，决定是哪个系统调用，a1为系统调用的参数。由于只有几个系统调用，所以可以用li指令来构造参数，且只有一个寄存器传参。 linux下的系统调用很多，其call convention如下，可以最多支持6个参数传递，再多就只能放栈上了。
Arch/ABI Instruction System Ret Ret Error Notes
call # val val2
───────────────────────────────────────────────────────────────────
alpha callsys v0 v0 a4 a3 1, 6
arc trap0 r8 r0 - -
arm/OABI swi NR - r0 - - 2
arm/EABI swi 0x0 r7 r0 r1 -
arm64 svc #0 w8 x0 x1 -
blackfin excpt 0x0 P0 R0 - -
i386 int $0x80 eax eax edx -
ia64 break 0x100000 r15 r8 r9 r10 1, 6
m68k trap #0 d0 d0 - -
microblaze brki r14,8 r12 r3 - -
mips syscall v0 v0 v1 a3 1, 6
nios2 trap r2 r2 - r7
parisc ble 0x100(%sr2, %r0) r20 r28 - -
powerpc sc r0 r3 - r0 1
powerpc64 sc r0 r3 - cr0.SO 1
riscv ecall a7 a0 a1 -
s390 svc 0 r1 r2 r3 - 3
s390x svc 0 r1 r2 r3 - 3
superh trapa #31 r3 r0 r1 - 4, 6
sparc/32 t 0x10 g1 o0 o1 psr/csr 1, 6
sparc/64 t 0x6d g1 o0 o1 psr/csr 1, 6
tile swint1 R10 R00 - R01 1
x86-64 syscall rax rax rdx - 5
x32 syscall rax rax rdx - 5
xtensa syscall a2 a2 - -
spike
spike 是完整的用户态CPU模拟器，同时支持Machine Mode/Hypervisor Mode/User Mode的模拟，在启动的时候会自己通过定义分配用户态栈空间。系统调用、指令crash都会被记录，并通过openocd模拟jtag方式告诉用户。proxy kernel是一个最简单的软核心，自带bootloader，可以通过bootloader后启动一个最小linux跑任意riscv elf文件，但是支持的syscall有限。
调试和编译方法如下，详细介绍请见官网。
riscv64-unknown-elf-gcc -march=rv32imac -mabi=ilp32 -g -Og -T spike.lds -nostartfiles -o [file] ./[file].c
spike --rbb-port=9824 -m0x10000000:0x20000 [file]
#another shell for probing the output and open port for debugging
openocd -f spike.cfg
#another shell for gdb
riscv64-unknown-elf-gdb [file]
-> target remote :3333
qemu
qemu是模拟届的永远的神，在qemu出来以前，我们需要通过真的在体制好的CPU及外设上进行调试操作系统，且需要实时查看硬件错误码，而qemu完整的模拟了硬件的状态，新硬件出来时，硬件厂商会给予第一步支持。
qemu-user-static
用户态模拟qemu，内部自带一个linux handler。