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This article will explain in detail how to build an X86 assembly debugging environment. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

Build the assembly environment

This time using vscode to build, the required plug-ins are X86 and X86room64 Assembly (you can also use the masm plug-in), as well as a hexdump for VSCode.

Install NASM and add to the environment variable

Install QEMU and add it to the environment variable

Write code: (code from 30-day homemade operating system)

; hello-os; TAB=4; standard FAT12 format floppy disk specific code Stand FAT12 format floppy code DB 0xeb, 0x4e, 0x90 DB "HELLOIPL"; boot sector name (8 bytes) DW 512; each sector (sector) size (must 512 bytes) DB 1 Cluster (cluster) size (must be 1 sector) DW 1; FAT start position (usually the first sector) DB 2; number of FAT (must be 2) DW 224; root directory size (usually 224 entries) DW 2880 The disk size (must be 2880 sectors 1440mm 1024ap512) DB 0xf0; disk type (must be 0xf0) DW 9; length of FAT (must be 9 sectors) DW 18; one track (track) has several sectors (must be 18) DW 2 Number of heads (must be 2) DD 0; do not use partitions, must be 0 DD 2880; rewrite disk size; I found two lines of code in the book that the author said was unexplained, see https://www.ntfs.com/fat-partition-sector.htm DB 0 BPB_Physical_Disk_Number DB (This is related to the BIOS physical disk number. Floppy drives are numbered starting with 0x00 for the A disk. Physical hard disks are numbered starting with 0x80. The value is typically 0x80 for hard disks, regardless of how many physical disk drives exist, because the value is only relevant if the device is the startup disk.) DB 0; BPB_Current_Head DB (Not used by FAT file system) DB 0x29; BPB_Signature DB (Must be either 0x28 or 0x29 in order to be recognized by Windows NT.) DD 0xffffffff; BPB_Volume_Serial_Number DD DB "HELLO-OS"; disk name (must be 11 bytes, insufficient blanks) DB "FAT12"; disk format name (must be 8 bytes, insufficient blanks) TIMES 18 DB 0; vacate 18 bytes first Program body DB 0xb8, 0x00, 0x00, 0x8e, 0xd0, 0xbc, 0x00, 0x7c DB 0x8e, 0xd8, 0x8e, 0xc0, 0xbe, 0x74, 0x7c, 0x8a DB 0x04, 0x83, 0xc6, 0x01, 0x3c, 0x00, 0x74, 0x09 DB 0xb4, 0x0e, 0xbb, 0x0f, 0x00, 0xcd, 0x10, 0xeb DB 0xee, 0xf4, 0xeb, 0xfd; Information display part DB 0x0a, 0x0a DB "hello, world" DB 0x0a twice; line wrap DB 0 TIMES 0x1fe-($- $$) DB 0x00; fill in 0x00 until 0x001fe DB 0x55, 0xaa Output DB 0xf0, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00 TIMES 4600 DB 0 DB 0xf0, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00 TIMES 1469432 DB 0 outside the boot sector; just change RESB 20 to TIMES 20 DB 0

Compile command

Run directly at the terminal after the vscode is written.

Nasm-f bin day1.asm-o day1.img

-f specifies that the output format is bin, and the img file is generated this time, because it is needed for subsequent debugging. Of course, other types of files can also be generated.

Run command

Qemu-system-i386 day1.img

Running result:

Debugging environment building

Debugging and assembling We usually use bochs software to debug.

Download link

Go to the installation directory and find a person named bochsdbg. Exe program, we mainly use this program in debugging

Open it and you will see the following interface

Click the Disk & Boot option in the white menu box and select First HD/CD on channel under ATA channel 0

Modify the following parameters

The first is specified as a disk

The second specifies the path to the img file

Heads: number of heads

Sectors per track: how many sectors are there per track

These parameters are actually specified by the program specified by the program above

DW 18; one track (track) has several sectors (must be 18) DW 2; number of heads (must be 2)

Then click boot drive in Boot Options to set it to disk.

Click ok and go back to the Bochs start menu menu. Click start to start debugging.

It's shown here.

Note that the bottom s actually means single-step debugging, and note that the line of assembly code shown is actually not running and will be run next time, such as here

Jmpf 0xf000:e05b

It is not actually running. You need to enter s to run this step

What if you want to jump to an address such as 0x7c00?

Enter b 0x7c00 b to run the breakpoint.

Type c again, which means continue continues, and you can jump to this.

You need to type Q twice if you want to quit.

Do you have any orders to add in the future?

It is important to note that the assembly code must be added with the previous fat code, otherwise bochs cannot be debugged, another way is to use FixVhdw.

This is the end of this article on "how to build an X86 assembly debugging environment". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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