如何使用GDB调试交叉编译的QEMU程序? [英] How to debug cross-compiled QEMU program with GDB?
问题描述
我无法调试使用GDB在QEMU中运行的简单程序. GDB似乎无法找到我在程序中的位置(因为它始终将??显示为我的当前位置)，并且它从未达到我设置的任何断点.
I'm having trouble debugging a simple program running in QEMU with GDB. GDB seems unable to find where I am in the program (in that it always displays ?? as my current location), and it never hits any breakpoint I set.
在一个终端中，我运行QEMU:
In one terminal, I run QEMU:
$ cat add.c
int main() {
int x = 9;
int v = 1;
while (1) {
int q = x + v;
}
return 0;
}
$ riscv64-unknown-elf-gcc add.c -g
$ qemu-system-riscv64 -gdb tcp::1234 -drive file=a.out,format=raw
在另一个终端中，我运行GDB:
And in another terminal, I run GDB:
$ riscv64-unknown-elf-gdb a.out
GNU gdb (GDB) 8.2.90.20190228-git
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=x86_64-apple-darwin17.7.0 --target=riscv64-unknown-elf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from a.out...
(gdb) target remote :1234
Remote debugging using :1234
0x0000000000000000 in ?? ()
(gdb) list
1 int main() {
2 int x = 9;
3 int v = 1;
4 while (1) {
5 int q = x + v;
6 }
7 return 0;
8 }
(gdb) b main
Breakpoint 1 at 0x1018e: file add.c, line 2.
(gdb) b 5
Breakpoint 2 at 0x1019a: file add.c, line 5.
(gdb) b _start
Breakpoint 3 at 0x10114
(gdb) b 4
Breakpoint 4 at 0x101a8: file add.c, line 4.
(gdb) c
Continuing.
即使程序应该无限循环，我也从未遇到断点.它显示0x0000000000000000 in ?? ()似乎很奇怪...但是也许可以吗?
I never hit a breakpoint, even though the program should be looping infinitely. It seems odd that it's displaying 0x0000000000000000 in ?? ()...but maybe that's okay?
我在这里做错了什么?我如何逐步完成该程序?
What am I doing wrong here? How can I step through this program?
推荐答案
我认为您缺少链接描述文件和一些启动代码-免责声明:我是riscv的新手.
您可以在Internet上找到有关这两个主题的很多信息，但是基本上您需要指定程序在RAM中的位置，以建立堆栈并初始化帧指针:
如果您希望能够调用函数并在程序中声明自动C变量(如a，b，c)，则必须这样做.
I think you are missing a linker script and some startup code - disclaimer: I am a newcomer to riscv.
You will find a lot of information on those two topics on the Internet, but you basically need to specify where your program will be located in RAM, to establish a stack and initialize the frame pointer:
This is required if you want to be able to call functions and declare automatic C variables like a, b, c in your program.
我使用了Windows 此处.
I used the Windows toolchain from Kendryte for the purpose of this example (the Linux version is available here), and a Windows version of qemu retrieved here.
1)链接描述文件:该示例使用了riscv64-unknown-elf-ld使用的默认链接描述文件的稍微修改的示例:
1) Linker script: the example uses a slightly modified example of the default linker script used by riscv64-unknown-elf-ld:
riscv64-unknown-elf-ld --verbose > riscv64-virt.ld
编辑riscv64-virt.ld，并仅保留以下行分隔的行:
Edit riscv64-virt.ld, and keep only the lines delimited by:
==================================================
添加有关qemu-system-riscv64 virt计算机的内存布局的描述:
Add a description for the memory layout of the qemu-system-riscv64 virt machine:
OUTPUT_ARCH(riscv)
MEMORY
{
/* qemu-system-risc64 virt machine */
RAM (rwx) : ORIGIN = 0x80000000, LENGTH = 128M
}
ENTRY(_start)
使用ORIGIN(RAM)和LENGTH(RAM)代替硬编码值，并提供__stack_top符号:
Use ORIGIN(RAM) and LENGTH(RAM) instead of hard-coded values, and provide a __stack_top symbol:
PROVIDE (__executable_start = SEGMENT_START("text-segment", ORIGIN(RAM))); . = SEGMENT_START("text-segment", ORIGIN(RAM)) + SIZEOF_HEADERS;
PROVIDE(__stack_top = ORIGIN(RAM) + LENGTH(RAM));
顺便说一句，有很多方法可以学习qemu系统目标机器的内存布局，但是我通常看一下它的设备树文件:
By the way, there are multiple ways of learning the memory layout of a qemu-system target machine, but I usually look at its Device Tree file:
qemu-system-riscv64 -machine virt -machine dumpdtb=riscv64-virt.dtb
dtc -I dtb -O dts -o riscv-virt.dts riscv-virt.dtb
描述内存的部分告诉我们它从0x80000000开始:
The section describing the memory tells us it starts at 0x80000000:
memory@80000000 {
device_type = "memory";
reg = <0x0 0x80000000 0x0 0x8000000>;
};
riscv64-virt.ld:
riscv64-virt.ld:
/* Script for -z combreloc: combine and sort reloc sections */
/* Copyright (C) 2014-2018 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-littleriscv", "elf64-littleriscv",
"elf64-littleriscv")
OUTPUT_ARCH(riscv)
MEMORY
{
/* qemu-system-risc64 virt machine */
RAM (rwx) : ORIGIN = 0x80000000, LENGTH = 128M
}
ENTRY(_start)
SECTIONS
{
/* Read-only sections, merged into text segment: */
PROVIDE (__executable_start = SEGMENT_START("text-segment", ORIGIN(RAM))); . = SEGMENT_START("text-segment", ORIGIN(RAM)) + SIZEOF_HEADERS;
PROVIDE(__stack_top = ORIGIN(RAM) + LENGTH(RAM));
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the same address within the page on the next page up. */
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*(.tdata .tdata.* .gnu.linkonce.td.*)
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.preinit_array :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array))
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KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
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PROVIDE_HIDDEN (__init_array_end = .);
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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 = .);
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the constructors, so we make sure it is
first. Because this is a wildcard, it
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KEEP (*crtbegin?.o(.ctors))
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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))
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2) startup.s: (credits: here and here).
.section .init, "ax"
.global _start
_start:
.cfi_startproc
.cfi_undefined ra
.option push
.option norelax
la gp, __global_pointer$
.option pop
la sp, __stack_top
add s0, sp, zero
jal zero, main
.cfi_endproc
.end
add.c :(您的代码)
add.c: (your code)
int main() {
int a = 4;
int b = 12;
while (1) {
int c = a + b;
}
return 0;
}
3)编译/链接并创建列表:
3) compiling/linking, and creating a listing:
riscv64-unknown-elf-gcc -g -ffreestanding -O0 -Wl,--gc-sections -nostartfiles -nostdlib -nodefaultlibs -Wl,-T,riscv64-virt.ld -o add.elf startup.s add.c
riscv64-unknown-elf-objdump -D add.elf > add.objdump
4)在控制台中启动qemu:
4) starting qemu in a console:
qemu-system-riscv64 -machine virt -m 128M -gdb tcp::1234,ipv4 -kernel add.elf
我不确定您使用的qemu选项:-drive file=a.out,format=raw
是正确的，但我认为不是，但是我没有花时间检查，而是使用了我通常使用的选项:-kernel add.elf
I am not sure that the qemu options you were using: -drive file=a.out,format=raw
are correct, and I think they are not, but I did not spend time checking, and used the options I am usually using: -kernel add.elf
4)在另一个控制台中启动gdb(为了方便自己，我在这里使用的是GUI编译的TDB支持的GDB).
4) starting gdb in another console (I am using here a GDB I compiled with TUI support for mingw64 for my own convenience).
riscv64-elf-gdb --tui add.elf
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
main () at add.c:5
(gdb) p a
$1 = 4
(gdb) p b
$2 = 12
(gdb) p c
$3 = 16
(gdb)
这可能有点长，但是我希望这会有所帮助. 请注意，启动代码足以满足您的代码要求，但是缺少一些重要的初始化操作，例如将数据部分从闪存复制到RAM(此处不相关)，以及清除.bss部分.
This may have been a little bit long, but I hope this will help. Please note that the startup code is good enough for your code, but some important initializations are missing, such as copying the data section from flash to RAM (not relevant here), and clearing the .bss section.
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