fix tls update issue

[betahxy]

Summary of this Pull Request (PR)

We already have updating tls logic when thread switches. Thus the only problem here is to remove save & restore %fs an %gs registers in entry.S. Also, in order to keep the pt_regs struct original logic, we can simply add & sub %rsp when there is an exception, no need to to push and pop. This will also fix that print regs problem, now it can correctly print all registers when there is a BUG()/assert().

Intent for your PR

Choose one (Mandatory):

• [x] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [ ] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

@gparmer

Code Quality

As part of this pull request, I've considered the following:

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [x] Naming adhere's to the SG
• [x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• [ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• [x] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

• [ ] micro_booter
• [x] unit_pingpong
• [ ] unit_schedtests
• [ ] ...(add others here)

[gparmer]

When you want to flip this over to "mature and ready for integration", let me know.

[gparmer]

You still have this marked for code review, and not as mature and ready for application. Can we move this along and apply it? I'm not sure what the hold up is.