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cmd/compile/abi-internal: mention SSE restriction on Plan 9

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Change-Id: I2be08b88b5147cf37ac55b7472d63503739c9f05
Reviewed-on: https://go-review.googlesource.com/c/go/+/369156
Trust: Austin Clements <austin@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-12-03 13:40:10 -05:00
parent ebe99189fc
commit b3e1fbff4d
1 changed files with 5 additions and 1 deletions
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6
src/cmd/compile/abi-internal.md
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@ -410,7 +410,11 @@ Special-purpose registers are as follows:
| R13 | Scratch | Scratch | Scratch |
| R14 | Current goroutine | Same | Same |
| R15 | GOT reference temporary if dynlink | Same | Same |
| X15 | Zero value | Same | Scratch |
| X15 | Zero value (*) | Same | Scratch |
(*) Except on Plan 9, where X15 is a scratch register because SSE
registers cannot be used in note handlers (so the compiler avoids
using them except when absolutely necessary).
*Rationale*: These register meanings are compatible with Go’s
stack-based calling convention except for R14 and X15, which will have