The branch main has been updated by kib:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=0e6b06d5c8719597b2ec59e6856b5decbd9e65f6

commit 0e6b06d5c8719597b2ec59e6856b5decbd9e65f6
Author:     Konstantin Belousov <[email protected]>
AuthorDate: 2021-12-13 23:25:36 +0000
Commit:     Konstantin Belousov <[email protected]>
CommitDate: 2021-12-14 17:14:40 +0000

    x86: add a comment providing source for numbers in legacy XSAVE area layout
    
    Suggested by:   Michael Pratt <[email protected]>
    Reviewed by:    Michael Pratt <[email protected]>, emaste
    Sponsored by:   The FreeBSD Foundation
    MFC after:      3 days
    Differential revision:  https://reviews.freebsd.org/D33423
---
 sys/amd64/amd64/fpu.c | 3 ++-
 sys/i386/i386/npx.c   | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/sys/amd64/amd64/fpu.c b/sys/amd64/amd64/fpu.c
index daf079b7d2cc..9b23cc5773a3 100644
--- a/sys/amd64/amd64/fpu.c
+++ b/sys/amd64/amd64/fpu.c
@@ -472,7 +472,8 @@ fpuinitstate(void *arg __unused)
 
        /*
         * Create a table describing the layout of the CPU Extended
-        * Save Area.
+        * Save Area.  See Intel SDM rev. 075 Vol. 1 13.4.1 "Legacy
+        * Region of an XSAVE Area" for the source of offsets/sizes.
         */
        if (use_xsave) {
                xstate_bv = (uint64_t *)((char *)(fpu_initialstate + 1) +
diff --git a/sys/i386/i386/npx.c b/sys/i386/i386/npx.c
index 4767d8896de9..dc04d84b0eb5 100644
--- a/sys/i386/i386/npx.c
+++ b/sys/i386/i386/npx.c
@@ -527,7 +527,10 @@ npxinitstate(void *arg __unused)
 
        /*
         * Create a table describing the layout of the CPU Extended
-        * Save Area.
+        * Save Area.  See Intel SDM rev. 075 Vol. 1 13.4.1 "Legacy
+        * Region of an XSAVE Area" for the source of offsets/sizes.
+        * Note that 32bit XSAVE does not use %xmm8-%xmm15, see
+        * 10.5.1.2 and 13.5.2 "SSE State".
         */
        if (use_xsave) {
                xstate_bv = (uint64_t *)((char *)(npx_initialstate + 1) +

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