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ptitSeb / box64

Box64 - Linux Userspace x86_64 Emulator with a twist, targeted at ARM64 Linux devices
https://box86.org
MIT License
3.73k stars 267 forks source link

Fix X64 FS_BASE #1638

Closed Coekjan closed 1 month ago

Coekjan commented 2 months ago

I found that mov %fs:0x0, %rax in my application got wrong FS BASE. After investigation, I found that my_context->segtls[idx].key (where idx = 8 in my case corresponding to FS BASE) is not correctly initialized. I modified the if-statement condition and my app is working well now.

I am not very sure if my patch is correct. If I am wrong, please correct me.

Coekjan commented 2 months ago

In addition, I see line 178: for (int i=9; i<15 && idx==-1; ++i). I don't understand why the for-loop starts from 9 (I am not familiar with x64 architecture), could you please give me some hints or information about it?

ptitSeb commented 2 months ago

I don't remember those stuff. I did that some time ago and didn't touched it. I just remember it's very sensitive. I have to go back in the code to understand/remember what desciptor 8 is...

Coekjan commented 2 months ago

To reproduce the issue, download the newest version (1.36.1-2) of busybox from archlinux archive ( https://archive.archlinux.org/packages/b/busybox/ ), and run it with box64:

$ box64 busybox ls
ptitSeb commented 1 month ago

So, "8" is the selector used by libc for it's tls stuffs. That's why it's handled as a spacial case, to be abble to wrap libc correctly.

I suppose on you side, the program you are using is statically linked, wich is still not really supported with box64. While I can do a special case to check if libc is currently used and if not, allow the selector 8, there are still some other stuffs, like "threads", that will probably badly behave because box64 use libphtread internaly, and that will conflict with staticaly linked pthread on your program I think.

Coekjan commented 1 month ago

@ptitSeb if statically-linked programs are not planned to support yet, I will close this PR (even if we plan to support those programs, this PR is not doing the right thing)