bx_dbg_read_linear: physical memory read error on chapter 2 First Steps #20

arun-mani-j · 2024-09-21T09:37:13Z

arun-mani-j
Sep 21, 2024

Hii all.

I followed the exact steps and copied the code verbatim under https://ordoflammae.github.io/littleosbook/#hello-cafebabe.
The only change I did is, using sdl2 instead of sdl in Bochs' configuration.

This is what I get when I run bochs -f bochsrc.txt -q:

00000000000i[      ] LTDL_LIBRARY_PATH not set. using compile time default '/usr/lib/x86_64-linux-gnu/bochs/plugins'
========================================================================
                        Bochs x86 Emulator 2.8
             Built from GitHub snapshot on March 10, 2024
                Timestamp: Sun Mar 10 08:00:00 CET 2024
========================================================================
00000000000i[      ] BXSHARE not set. using compile time default '/usr/share/bochs'
00000000000i[      ] lt_dlhandle is 0x55da8b081160
00000000000i[PLUGIN] loaded plugin libbx_parallel.so
00000000000i[      ] lt_dlhandle is 0x55da8b082e00
00000000000i[PLUGIN] loaded plugin libbx_speaker.so
00000000000i[      ] lt_dlhandle is 0x55da8b083ee0
00000000000i[PLUGIN] loaded plugin libbx_biosdev.so
00000000000i[      ] lt_dlhandle is 0x55da8b084920
00000000000i[PLUGIN] loaded plugin libbx_gameport.so
00000000000i[      ] lt_dlhandle is 0x55da8b0851b0
00000000000i[PLUGIN] loaded plugin libbx_extfpuirq.so
00000000000i[      ] lt_dlhandle is 0x55da8b085a10
00000000000i[PLUGIN] loaded plugin libbx_iodebug.so
00000000000i[      ] lt_dlhandle is 0x55da8b086290
00000000000i[PLUGIN] loaded plugin libbx_serial.so
00000000000i[      ] lt_dlhandle is 0x55da8b08a490
00000000000i[PLUGIN] loaded plugin libbx_unmapped.so
00000000000i[      ] reading configuration from bochsrc.txt
00000000000i[      ] lt_dlhandle is 0x55da8b08af50
00000000000i[PLUGIN] loaded plugin libbx_textconfig.so
00000000000i[      ] lt_dlhandle is 0x55da8b08b6e0
00000000000i[PLUGIN] loaded plugin libbx_sdl2_gui.so
00000000000i[      ] installing sdl2 module as the Bochs GUI
00000000000i[SDL2  ] maximum host resolution: x=1920 y=1080
00000000000i[      ] using log file bochslog.txt
Bochs internal debugger, type 'help' for help or 'c' to continue
Switching to CPU0
Next at t=0
(0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmpf 0xf000:e05b          ; ea5be000f0
<bochs:1> c
bx_dbg_read_linear: physical memory read error (phy=0x0000322f3331, lin=0x00000000322f3331)
Next at t=662802
(0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmpf 0xf000:e05b          ; ea5be000f0
<bochs:2> c
bx_dbg_read_linear: physical memory read error (phy=0x0000322f3331, lin=0x00000000322f3331)
Next at t=1325794
(0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmpf 0xf000:e05b          ; ea5be000f0
<bochs:3> c
bx_dbg_read_linear: physical memory read error (phy=0x0000322f3331, lin=0x00000000322f3331)
Next at t=1988672
(0) [0x0000fffffff0] f000:fff0 (unk. ctxt): jmpf 0xf000:e05b          ; ea5be000f0
<bochs:4> q
(0).[1988672] [0x0000fffffff0] f000:fff0 (unk. ctxt): jmpf 0xf000:e05b          ; ea5be000f0

This is my bochslog.txt.

I'm on Debian GNU/Linux Trixie/Sid with Bochs 2.8.

What am I doing wrong, thanks in advance!

Answered by arun-mani-j

Sep 28, 2024

I must have been wearing my lucky hat - I got so nervous, I tried the images available in Bochs' sample images and they also had the same issue. I reinstalled packages, changed memory limits but everything failed with same error.

Then I tried searching for the errors in web, though most of them were due to buggy programs... then I found this AskUbuntu post - https://askubuntu.com/questions/1521719/bochs-cant-access-bootloader-address-0x7c00-error-physical-memory-read-error and the answer by the OP themselves:

aparrently because of a new update bochs pushed it kinda messed with the romimage on Ubuntu as a quick fix instead of using the latest i used the legacy bios so instead of:
romimage…

View full answer

arun-mani-j · 2024-09-23T13:30:52Z

arun-mani-j
Sep 23, 2024
Author

chapter-2.zip

The files of concern as discussed in #18

0 replies

OrdoFlammae · 2024-09-23T19:25:17Z

OrdoFlammae
Sep 23, 2024
Maintainer

@arun-mani-j, I stepped through all the different steps, comparing my files to yours, and it appears that everything becomes different when you create your ISO file. All the binaries before that are identical. Additionally, when I run my ISO, it works perfectly. What is your grub setup? Any logs or warnings when running grub-mkrescue -o os.iso iso? My guess is that the issue originates there.

5 replies

OrdoFlammae Sep 26, 2024
Maintainer

My logs are almost identical. When I got a chance, I mounted your ISO and mine to see what the difference between the two was. The first thing that stood out to me was that your ISO is missing all the i386 files, only including x86_64 files. I don't know entirely why this is, you'd probably have to do some probing into your GRUB installation, but it appears that your installation is missing some crucial pieces. Note that BOCHS emulates an IA32 system, not a 64-bit system, so I would guess that this is your problem.

Once you figure out what packages you need to install to fix this issue, please let me know and/or create a PR to add a note to the book for future users.

Your ISO's folders:

2.4M	test/boot/grub/fonts
5.0M	test/boot/grub/locale
2.0K	test/boot/grub/roms
2.8M	test/boot/grub/x86_64-efi
10M		test/boot/grub
10M		test/boot
202K	test/efi/boot
204K	test/efi
205K	test/System/Library/CoreServices
207K	test/System/Library
209K	test/System
2.0K	test/.disk
14M		test

My ISO's folders:

2.4M	test2/boot/grub/fonts
2.0M	test2/boot/grub/i386-efi
2.1M	test2/boot/grub/i386-pc
11M		test2/boot/grub/locale
2.0K	test2/boot/grub/roms
2.8M	test2/boot/grub/themes/starfield
2.8M	test2/boot/grub/themes
2.7M	test2/boot/grub/x86_64-efi
23M		test2/boot/grub
23M		test2/boot
498K	test2/efi/boot
500K	test2/efi
354K	test2/System/Library/CoreServices
356K	test2/System/Library
358K	test2/System
2.0K	test2/.disk
27M		test2

arun-mani-j Sep 27, 2024
Author

Thanks, I seem to be missing grub-pc-bin for the pc files and grub-efi-ia32-bin for the i386 files.

This is my image contents now:

$ tree -L 3 /media/arun-mani-j/ISOIMAGE/
/media/arun-mani-j/ISOIMAGE/
├── boot
│   ├── grub
│   │   ├── fonts
│   │   ├── grub.cfg
│   │   ├── i386-efi
│   │   ├── i386-pc
│   │   ├── locale
│   │   ├── roms
│   │   └── x86_64-efi
│   └── kernel.elf
├── efi
│   └── boot
│       ├── boot.efi
│       ├── bootia32.efi
│       └── bootx64.efi
├── mach_kernel
└── System
    └── Library
        └── CoreServices

But running bochs still gives the physical memory read error. :(

These are the packages I have regarding grub:

$ apt list --installed | grep grub-
grub-common/testing,now 2.12-5 amd64 [installed]
grub-efi-amd64-bin/testing,now 2.12-5 amd64 [installed,automatic]
grub-efi-amd64-signed/testing,now 1+2.12+5 amd64 [installed,automatic]
grub-efi-amd64-unsigned/testing,now 2.12-5 amd64 [installed,automatic]
grub-efi-amd64/testing,now 2.12-5 amd64 [installed]
grub-efi-ia32-bin/testing,now 2.12-5 amd64 [installed]
grub-efi-ia32-unsigned/testing,now 2.12-5 amd64 [installed,automatic]
grub-pc-bin/testing,now 2.12-5 amd64 [installed]

And my os.iso:
os.zip

Can you upload your ISO file so I can check if it is not something wrong with my bochs? Thanks!

OrdoFlammae Sep 28, 2024
Maintainer

Yes, it does look like it's an issue with your bochs setup, I ran the ISO you attached and it worked perfectly. It's not exactly the same as my ISO, but I am wondering if GRUB just attaches every single file it has access to into the ISO.

I've attached my OS file here so you can test it, but I doubt you will get anything new.
os.zip

arun-mani-j Sep 28, 2024
Author

I must have been wearing my lucky hat - I got so nervous, I tried the images available in Bochs' sample images and they also had the same issue. I reinstalled packages, changed memory limits but everything failed with same error.

Then I tried searching for the errors in web, though most of them were due to buggy programs... then I found this AskUbuntu post - https://askubuntu.com/questions/1521719/bochs-cant-access-bootloader-address-0x7c00-error-physical-memory-read-error and the answer by the OP themselves:

aparrently because of a new update bochs pushed it kinda messed with the romimage on Ubuntu as a quick fix instead of using the latest i used the legacy bios so instead of:
romimage: file=/usr/share/bochs/BIOS-bochs-latest, address = 0xfffe0000
just put:
romimage: file=/usr/share/bochs/BIOS-bochs-legacy

Oh my, I tried it and it worked!!

This is what I have in my bochslog.txt:

00553148000p[SDL2  ] >>PANIC<< POWER button turned off.
00553148000i[CPU0  ] CPU is in protected mode (active)
00553148000i[CPU0  ] CS.mode = 32 bit
00553148000i[CPU0  ] SS.mode = 32 bit
00553148000i[CPU0  ] EFER   = 0x00000000
00553148000i[CPU0  ] | EAX=cafebabe  EBX=00010000  ECX=00000000  EDX=00000000
00553148000i[CPU0  ] | ESP=0007ff00  EBP=00000000  ESI=00000000  EDI=00000000
00553148000i[CPU0  ] | IOPL=0 id vip vif ac vm rf nt of df if tf sf ZF af PF cf
00553148000i[CPU0  ] | SEG sltr(index|ti|rpl)     base    limit G D
00553148000i[CPU0  ] |  CS:0010( 0002| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] |  DS:0018( 0003| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] |  SS:0018( 0003| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] |  ES:0018( 0003| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] |  FS:0018( 0003| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] |  GS:0018( 0003| 0|  0) 00000000 ffffffff 1 1
00553148000i[CPU0  ] | EIP=00100011 (00100011)
00553148000i[CPU0  ] | CR0=0x60000011 CR2=0x00000000
00553148000i[CPU0  ] | CR3=0x00000000 CR4=0x00000000
00553148000i[CMOS  ] Last time: 1727533210 tz=utc (Sat Sep 28 14:20:10   2024)
00553148000i[SIM   ] quit_sim called with exit code 1

Feels so good now!

The person asked the question just 2 months ago.

I tried downloading the RPM package from Bochs website itself - https://sourceforge.net/projects/bochs/files/bochs/2.7/. Then I extracted it and found the BIOS images it had.
I tried using the BIOS-bochs-latest from it and it worked fine.

So let me try reporting it to Debian.

Thanks a lot for helping through the process 😄 .

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bx_dbg_read_linear: physical memory read error on chapter 2 First Steps #20

arun-mani-j Sep 21, 2024

Replies: 2 comments · 5 replies

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arun-mani-j
Sep 23, 2024
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