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runtime: use one more address bit for tagged pointers

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We use one extra bit to placate systems which simulate amd64 binaries on
an arm64 host. Allocated arm64 addresses could be as high as 1<<48-1,
which would be invalid if we assumed 48-bit sign-extended addresses.

(Note that this does not help the other way around, simluating arm64
on amd64, but we don't have that problem at the moment.)

Fixes #69255

Change-Id: Iace17a5d41a65e34abf201d03d8b0ff6f7bf1150
Reviewed-on: https://go-review.googlesource.com/c/go/+/700515
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Keith Randall 2025-09-02 15:46:11 -07:00 • committed by Gopher Robot
parent b09068041a
commit 2a7f1d47b0
1 changed files with 8 additions and 1 deletions
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9
src/runtime/tagptr_64bit.go
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@ -22,10 +22,17 @@ const (
// On AMD64, virtual addresses are 48-bit (or 57-bit) sign-extended. // On AMD64, virtual addresses are 48-bit (or 57-bit) sign-extended.
// Other archs are 48-bit zero-extended. // Other archs are 48-bit zero-extended.
// //
// We use one extra bit to placate systems which simulate amd64 binaries on
// an arm64 host. Allocated arm64 addresses could be as high as 1<<48-1,
// which would be invalid if we assumed 48-bit sign-extended addresses.
// See issue 69255.
// (Note that this does not help the other way around, simluating arm64
// on amd64, but we don't have that problem at the moment.)
//
// On s390x, virtual addresses are 64-bit. There's not much we // On s390x, virtual addresses are 64-bit. There's not much we
// can do about this, so we just hope that the kernel doesn't // can do about this, so we just hope that the kernel doesn't
// get to really high addresses and panic if it does. // get to really high addresses and panic if it does.
defaultAddrBits = 48 defaultAddrBits = 48 + 1
// On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit // On AIX, 64-bit addresses are split into 36-bit segment number and 28-bit
// offset in segment. Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA) // offset in segment. Segment numbers in the range 0x0A0000000-0x0AFFFFFFF(LSA)