x86 FRED: add hardware definitions for the trap frames fields
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Authored by kib on Thu, Mar 12, 4:15 PM.

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jhb
markj

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rGe90950627327: x86 FRED: add hardware definitions for the trap frames fields

Summary

as provided by the Intel document 346446-009 AKA FRED 8.0 and SDM v90,
February 2026.

Note that the layout of the struct trapframe does not change with
FRED. The differences are in addition of two fields at the end of the
structure. Other members are carved from existing tf_cs and tf_ss by
limiting hw-written segments to 16 bits officially, and reusing rest
from the doubleword for the new data.

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rG FreeBSD src repository

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kib created this revision.Thu, Mar 12, 4:15 PM

Herald added a subscriber: imp. · View Herald TranscriptThu, Mar 12, 4:15 PM

kib requested review of this revision.Thu, Mar 12, 4:15 PM

markj added inline comments.Sat, Mar 14, 12:52 AM

sys/amd64/amd64/trap.c
944	No need anymore for the mask of tf_cs.
sys/x86/include/frame.h
148	The field prefix should be `tf_`.
152–157	Should we apply some explicit masking in places where `tf_ss` is assigned by software? e.g. in set_mcontext(), we have `tp->tf_ss = mcp->mc_ss`, so there is implicit truncation.
154	The numbering of the evinfo fields is a bit weird. I see why you did it this way, it follows the order that the fields are described in the FRED documentation. Probably not worth changing.

kib marked 4 inline comments as done.Sat, Mar 14, 10:55 AM

kib added inline comments.

sys/x86/include/frame.h
152–157	I do not object, but I do not see a purpose for explicit cast or masking. OTOH we indeed might consider adding checks that ss cs from the mcontext fits into 16 bits, i.e. the reserved bits are not passed by userspace.

Fix typo in the name of the reserved field.
Remove cs masking.

markj accepted this revision.Sun, Mar 15, 1:47 AM

markj added inline comments.

sys/x86/include/frame.h
152–157	Some checks would be good. I'm not sure if there is any chance that they would break compatibility somehow.

This revision is now accepted and ready to land.Sun, Mar 15, 1:47 AM

FYI, kgdb will have to know about the change in layout to trapframe I think, so bump __FreeBSD_version when you land this just to be on the safe side please?

In D55831#1279681, @jhb wrote:

FYI, kgdb will have to know about the change in layout to trapframe I think, so bump __FreeBSD_version when you land this just to be on the safe side please?

The trapframe layout does not change with FRED. The differences are in addition of two fields at the end of the structure. Other members are carved from existing tf_cs and tf_ss by limiting hw-written segments to 16 bits officially, and reusing rest from the doubleword for the new data.

sys/x86/include/frame.h
152–157	D55861

kib edited the summary of this revision. (Show Details)Thu, Mar 19, 3:46 PM

I can't recall if kgdb has to know the size of struct trapframe is my only concern. I think we already only use the 16 bits for cs/ss today.

In D55831#1279764, @jhb wrote:

I can't recall if kgdb has to know the size of struct trapframe is my only concern. I think we already only use the 16 bits for cs/ss today.

Ok, I will bump the version.

Is there the same concern for struct pcb? I need to add FRED MSRs to it.

Closed by commit rGe90950627327: x86 FRED: add hardware definitions for the trap frames fields (authored by kib). · Explain WhyFri, Mar 20, 10:50 PM

This revision was automatically updated to reflect the committed changes.

kib added a commit: rGe90950627327: x86 FRED: add hardware definitions for the trap frames fields.