cmd/internal/dwarf: always use AT_ranges for scopes with DWARF 5
This patch extends the change in CL 657175 to apply the same abbrev
selection strategy to single-range lexical scopes that we're now using
for inlined routine bodies, when DWARF 5 is in effect. Ranges are more
compact and use fewer relocation than explicit hi/lo PC values, so we
might as well always use them.
Updates #26379.
Change-Id: Ieeaddf50e82acc4866010e29af32bcd1fb3b4f02
Reviewed-on: https://go-review.googlesource.com/c/go/+/657177
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go
index 7673c3f..6e06f13 100644
--- a/src/cmd/internal/dwarf/dwarf.go
+++ b/src/cmd/internal/dwarf/dwarf.go
@@ -600,12 +600,8 @@
DW_TAG_lexical_block,
DW_CHILDREN_yes,
[]dwAttrForm{
- // Note: we can't take advantage of DW_FORM_addrx here,
- // since there is no way (at least at the moment) to
- // have an encoding for low_pc of the form "addrx + constant"
- // in DWARF5. If we wanted to use addrx, we'd need to create
- // a whole new entry in .debug_addr for the block start,
- // which would kind of defeat the point.
+ // Note: unused if we are generating DWARF 5, we
+ // use the ranges form even if there is a singleton range.
{DW_AT_low_pc, DW_FORM_addr},
{DW_AT_high_pc, DW_FORM_addr},
},
@@ -1526,7 +1522,10 @@
continue
}
- if len(scope.Ranges) == 1 {
+ // For DWARF 5, we always use the ranges form of the abbrev, since
+ // it is more compact than using explicit hi/lo PC attrs. See
+ // issue #72821 for more on why this makes sense.
+ if len(scope.Ranges) == 1 && !buildcfg.Experiment.Dwarf5 {
Uleb128put(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE)
putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].Start, s.StartPC)
putattr(ctxt, s.Info, DW_ABRV_LEXICAL_BLOCK_SIMPLE, DW_FORM_addr, DW_CLS_ADDRESS, scope.Ranges[0].End, s.StartPC)
