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runtime: use entry stack map at function entry
Currently, when the runtime looks up the stack map for a frame, it uses frame.continpc - 1 unless continpc is the function entry PC, in which case it uses frame.continpc. As a result, if continpc is the function entry point (which happens for deferred frames), it will actually look up the stack map *following* the first instruction. I think, though I am not positive, that this is always okay today because the first instruction of a function can never change the stack map. It's usually not a CALL, so it doesn't have PCDATA. Or, if it is a CALL, it has to have the entry stack map. But we're about to start emitting stack maps at every instruction that changes them, which means the first instruction can have PCDATA (notably, in leaf functions that don't have a prologue). To prepare for this, tweak how the runtime looks up stack map indexes so that if continpc is the function entry point, it directly uses the entry stack map. For #24543. Change-Id: I85aa818041cd26aff416f7b1fba186e9c8ca6568 Reviewed-on: https://go-review.googlesource.com/109349 Reviewed-by: Rick Hudson <rlh@golang.org>
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@ -248,10 +248,11 @@ func dumpframe(s *stkframe, arg unsafe.Pointer) bool {
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// Figure out what we can about our stack map
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pc := s.pc
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pcdata := int32(-1) // Use the entry map at function entry
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if pc != f.entry {
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pc--
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pcdata = pcdatavalue(f, _PCDATA_StackMapIndex, pc, nil)
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}
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pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, pc, nil)
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if pcdata == -1 {
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// We do not have a valid pcdata value but there might be a
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// stackmap for this function. It is likely that we are looking
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@ -2004,10 +2004,11 @@ func getgcmask(ep interface{}) (mask []byte) {
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if targetpc == 0 {
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return
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}
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pcdata := int32(-1) // Use the entry map at function entry
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if targetpc != f.entry {
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targetpc--
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pcdata = pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, nil)
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}
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pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, nil)
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if pcdata == -1 {
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return
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}
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@ -801,10 +801,15 @@ func scanframeworker(frame *stkframe, cache *pcvalueCache, gcw *gcWork) {
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if _DebugGC > 1 {
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print("scanframe ", funcname(f), "\n")
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}
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pcdata := int32(-1)
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if targetpc != f.entry {
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// Back up to the CALL. If we're at the function entry
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// point, we want to use the entry map (-1), even if
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// the first instruction of the function changes the
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// stack map.
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targetpc--
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pcdata = pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, cache)
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}
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pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, cache)
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if pcdata == -1 {
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// We do not have a valid pcdata value but there might be a
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// stackmap for this function. It is likely that we are looking
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@ -625,10 +625,11 @@ func adjustframe(frame *stkframe, arg unsafe.Pointer) bool {
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// have full GC info for it (because it is written in asm).
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return true
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}
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pcdata := int32(-1) // Use the entry map at function entry
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if targetpc != f.entry {
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targetpc--
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pcdata = pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, &adjinfo.cache)
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}
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pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc, &adjinfo.cache)
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if pcdata == -1 {
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pcdata = 0 // in prologue
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}
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