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author | Michael Anthony Knyszek <mknyszek@google.com> | 2021-02-18 17:33:01 +0000 |
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committer | Michael Knyszek <mknyszek@google.com> | 2021-03-05 15:34:32 +0000 |
commit | a2f70672334ecc71c81bd1f424e1734485d8cb83 (patch) | |
tree | d9de8f0be7b1d57cb02bb037854644cfe5c0acb4 /src/reflect | |
parent | c5a1c2276ee41a65cce93b7e443d333dfa29aba7 (diff) | |
download | go-a2f70672334ecc71c81bd1f424e1734485d8cb83.tar.gz go-a2f70672334ecc71c81bd1f424e1734485d8cb83.zip |
reflect: include the alignment of zero-sized types in stack offsets
This change modifies the reflect ABI assignment algorithm to catch
zero-sized types at the top level of each argument and faux-stack-assign
them. It doesn't actually generate an ABI step, which is unnecessary,
but it ensures that the offsets of further stack-assigned arguments are
aligned to the alignment of that zero-sized argument.
This change is necessary to have the register ABI assignment algorithm
gracefully degrade to ABI0 when no registers are present in the ABI.
Fixes #44377.
Change-Id: Ia95571688a61259302bb3c6d5fb33fbb6b5e8db8
Reviewed-on: https://go-review.googlesource.com/c/go/+/293789
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: Than McIntosh <thanm@google.com>
Diffstat (limited to 'src/reflect')
-rw-r--r-- | src/reflect/abi.go | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/src/reflect/abi.go b/src/reflect/abi.go index 618efd0980..50e6312172 100644 --- a/src/reflect/abi.go +++ b/src/reflect/abi.go @@ -123,6 +123,24 @@ func (a *abiSeq) stepsForValue(i int) []abiStep { func (a *abiSeq) addArg(t *rtype) *abiStep { pStart := len(a.steps) a.valueStart = append(a.valueStart, pStart) + if t.size == 0 { + // If the size of the argument type is zero, then + // in order to degrade gracefully into ABI0, we need + // to stack-assign this type. The reason is that + // although zero-sized types take up no space on the + // stack, they do cause the next argument to be aligned. + // So just do that here, but don't bother actually + // generating a new ABI step for it (there's nothing to + // actually copy). + // + // We cannot handle this in the recursive case of + // regAssign because zero-sized *fields* of a + // non-zero-sized struct do not cause it to be + // stack-assigned. So we need a special case here + // at the top. + a.stackBytes = align(a.stackBytes, uintptr(t.align)) + return nil + } if !a.regAssign(t, 0) { a.steps = a.steps[:pStart] a.stackAssign(t.size, uintptr(t.align)) |