ed1959c6e6
On amd64, the virtual address space, when interpreted as signed values, is [-2^47, 2^47). Currently, we only support heap addresses in the "positive" half of this, [0, 2^47). This suffices for linux/amd64 and windows/amd64, but solaris/amd64 can map user addresses in the negative part of this range. Specifically, addresses 0xFFFF8000'00000000 to 0xFFFFFD80'00000000 are part of user space. This leads to "memory allocated by OS not in usable address space" panic, since we don't map heap arena index space for these addresses. Fix this by offsetting addresses when computing arena indexes so that arena entry 0 corresponds to address -2^47 on amd64. We already map enough arena space for 2^48 heap addresses on 64-bit (because arm64's virtual address space is [0, 2^48)), so we don't need to grow any structures to support this. A different approach would be to simply mask out the top 16 bits. However, there are two advantages to the offset approach: 1) invalid heap addresses continue to naturally map to invalid arena indexes so we don't need extra checks and 2) it perturbs the mapping of addresses to arena indexes more, which helps check that we don't accidentally compute incorrect arena indexes somewhere that happen to be right most of the time. Several comments and constant names are now somewhat misleading. We'll fix that in the next CL. This CL is the core change the arena indexing. Fixes #23862. Change-Id: Idb8e299fded04593a286b01a9582da6ddbac2f9a Reviewed-on: https://go-review.googlesource.com/95497 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> |
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