cmd/compile,cmd/link: hooks for identifying coverage counters

Add a new "coverage counter" classification for variables to be used
for storing code coverage counter values (somewhat in the same way
that we identify fuzzer counters). Tagging such variables allows us to
aggregate them in the linker, and to treat updates specially.

Updates #51430.

Change-Id: Ib49fb05736ffece98bcc2f7a7c37e991b7f67bbb
Reviewed-on: https://go-review.googlesource.com/c/go/+/401235
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

4 files changed, 46 insertions, 23 deletions

diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index c2668b29a4..c23eac08a4 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -1074,6 +1074,8 @@ func dwarfblk(ctxt *Link, out *OutBuf, addr int64, size int64) {
 	writeBlocks(ctxt, out, ctxt.outSem, ctxt.loader, syms, addr, size, zeros[:])
 }
 
+var covCounterDataStartOff, covCounterDataLen uint64
+
 var zeros [512]byte
 
 var (
@@ -1781,6 +1783,15 @@ func (state *dodataState) allocateDataSections(ctxt *Link) {
 	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.enoptrbss", 0), sect)
 	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.end", 0), sect)
 
+	// Code coverage counters are assigned to the .noptrbss section.
+	// We assign them in a separate pass so that they stay aggregated
+	// together in a single blob (coverage runtime depends on this).
+	covCounterDataStartOff = sect.Length
+	state.assignToSection(sect, sym.SCOVERAGE_COUNTER, sym.SNOPTRBSS)
+	covCounterDataLen = sect.Length - covCounterDataStartOff
+	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.covctrs", 0), sect)
+	ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.ecovctrs", 0), sect)
+
 	// Coverage instrumentation counters for libfuzzer.
 	if len(state.data[sym.SLIBFUZZER_8BIT_COUNTER]) > 0 {
 		sect := state.allocateNamedSectionAndAssignSyms(&Segdata, "__sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, sym.Sxxx, 06)
@@ -2682,6 +2693,8 @@ func (ctxt *Link) address() []*sym.Segment {
 	ctxt.xdefine("runtime.edata", sym.SDATA, int64(data.Vaddr+data.Length))
 	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr))
 	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, int64(noptrbss.Vaddr+noptrbss.Length))
+	ctxt.xdefine("runtime.covctrs", sym.SCOVERAGE_COUNTER, int64(noptrbss.Vaddr+covCounterDataStartOff))
+	ctxt.xdefine("runtime.ecovctrs", sym.SCOVERAGE_COUNTER, int64(noptrbss.Vaddr+covCounterDataStartOff+covCounterDataLen))
 	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
 
 	if fuzzCounters != nil {
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index 5074ffa8c9..21a1466c49 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -453,6 +453,8 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	ctxt.xdefine("runtime.ebss", sym.SBSS, 0)
 	ctxt.xdefine("runtime.noptrbss", sym.SNOPTRBSS, 0)
 	ctxt.xdefine("runtime.enoptrbss", sym.SNOPTRBSS, 0)
+	ctxt.xdefine("runtime.covctrs", sym.SNOPTRBSS, 0)
+	ctxt.xdefine("runtime.ecovctrs", sym.SNOPTRBSS, 0)
 	ctxt.xdefine("runtime.end", sym.SBSS, 0)
 	ctxt.xdefine("runtime.epclntab", sym.SRODATA, 0)
 	ctxt.xdefine("runtime.esymtab", sym.SRODATA, 0)
@@ -529,7 +531,7 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	nsym := loader.Sym(ldr.NSym())
 	symGroupType := make([]sym.SymKind, nsym)
 	for s := loader.Sym(1); s < nsym; s++ {
-		if !ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) && ldr.SymPkg(s) != "" {
+		if (!ctxt.IsExternal() && ldr.IsFileLocal(s) && !ldr.IsFromAssembly(s) && ldr.SymPkg(s) != "") || (ctxt.LinkMode == LinkInternal && ldr.SymType(s) == sym.SCOVERAGE_COUNTER) {
 			ldr.SetAttrNotInSymbolTable(s, true)
 		}
 		if !ldr.AttrReachable(s) || ldr.AttrSpecial(s) || (ldr.SymType(s) != sym.SRODATA && ldr.SymType(s) != sym.SGOFUNC) {
@@ -672,6 +674,8 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ebss", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.noptrbss", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.enoptrbss", 0))
+	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.covctrs", 0))
+	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.ecovctrs", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.end", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcdata", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.gcbss", 0))
diff --git a/src/cmd/link/internal/sym/symkind.go b/src/cmd/link/internal/sym/symkind.go
index 0f8fbed878..2f8e8fe133 100644
--- a/src/cmd/link/internal/sym/symkind.go
+++ b/src/cmd/link/internal/sym/symkind.go
@@ -98,6 +98,8 @@ const (
 	SBSS
 	SNOPTRBSS
 	SLIBFUZZER_8BIT_COUNTER
+	SCOVERAGE_COUNTER
+	SCOVERAGE_AUXVAR
 	STLSBSS
 	SXREF
 	SMACHOSYMSTR
@@ -144,6 +146,8 @@ var AbiSymKindToSymKind = [...]SymKind{
 	objabi.SDWARFLOC:               SDWARFLOC,
 	objabi.SDWARFLINES:             SDWARFLINES,
 	objabi.SLIBFUZZER_8BIT_COUNTER: SLIBFUZZER_8BIT_COUNTER,
+	objabi.SCOVERAGE_COUNTER:       SCOVERAGE_COUNTER,
+	objabi.SCOVERAGE_AUXVAR:        SCOVERAGE_AUXVAR,
 }
 
 // ReadOnly are the symbol kinds that form read-only sections. In some
diff --git a/src/cmd/link/internal/sym/symkind_string.go b/src/cmd/link/internal/sym/symkind_string.go
index 14b57db41f..1cd7ab17ef 100644
--- a/src/cmd/link/internal/sym/symkind_string.go
+++ b/src/cmd/link/internal/sym/symkind_string.go
@@ -45,31 +45,33 @@ func _() {
 	_ = x[SBSS-34]
 	_ = x[SNOPTRBSS-35]
 	_ = x[SLIBFUZZER_8BIT_COUNTER-36]
-	_ = x[STLSBSS-37]
-	_ = x[SXREF-38]
-	_ = x[SMACHOSYMSTR-39]
-	_ = x[SMACHOSYMTAB-40]
-	_ = x[SMACHOINDIRECTPLT-41]
-	_ = x[SMACHOINDIRECTGOT-42]
-	_ = x[SFILEPATH-43]
-	_ = x[SDYNIMPORT-44]
-	_ = x[SHOSTOBJ-45]
-	_ = x[SUNDEFEXT-46]
-	_ = x[SDWARFSECT-47]
-	_ = x[SDWARFCUINFO-48]
-	_ = x[SDWARFCONST-49]
-	_ = x[SDWARFFCN-50]
-	_ = x[SDWARFABSFCN-51]
-	_ = x[SDWARFTYPE-52]
-	_ = x[SDWARFVAR-53]
-	_ = x[SDWARFRANGE-54]
-	_ = x[SDWARFLOC-55]
-	_ = x[SDWARFLINES-56]
+	_ = x[SCOVERAGE_COUNTER-37]
+	_ = x[SCOVERAGE_AUXVAR-38]
+	_ = x[STLSBSS-39]
+	_ = x[SXREF-40]
+	_ = x[SMACHOSYMSTR-41]
+	_ = x[SMACHOSYMTAB-42]
+	_ = x[SMACHOINDIRECTPLT-43]
+	_ = x[SMACHOINDIRECTGOT-44]
+	_ = x[SFILEPATH-45]
+	_ = x[SDYNIMPORT-46]
+	_ = x[SHOSTOBJ-47]
+	_ = x[SUNDEFEXT-48]
+	_ = x[SDWARFSECT-49]
+	_ = x[SDWARFCUINFO-50]
+	_ = x[SDWARFCONST-51]
+	_ = x[SDWARFFCN-52]
+	_ = x[SDWARFABSFCN-53]
+	_ = x[SDWARFTYPE-54]
+	_ = x[SDWARFVAR-55]
+	_ = x[SDWARFRANGE-56]
+	_ = x[SDWARFLOC-57]
+	_ = x[SDWARFLINES-58]
 }
 
-const _SymKind_name = "SxxxSTEXTSELFRXSECTSMACHOPLTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSFirstWritableSBUILDINFOSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASXCOFFTOCSBSSSNOPTRBSSSLIBFUZZER_8BIT_COUNTERSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSDYNIMPORTSHOSTOBJSUNDEFEXTSDWARFSECTSDWARFCUINFOSDWARFCONSTSDWARFFCNSDWARFABSFCNSDWARFTYPESDWARFVARSDWARFRANGESDWARFLOCSDWARFLINES"
+const _SymKind_name = "SxxxSTEXTSELFRXSECTSMACHOPLTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSFirstWritableSBUILDINFOSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASXCOFFTOCSBSSSNOPTRBSSSLIBFUZZER_8BIT_COUNTERSCOVERAGE_COUNTERSCOVERAGE_AUXVARSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSDYNIMPORTSHOSTOBJSUNDEFEXTSDWARFSECTSDWARFCUINFOSDWARFCONSTSDWARFFCNSDWARFABSFCNSDWARFTYPESDWARFVARSDWARFRANGESDWARFLOCSDWARFLINES"
 
-var _SymKind_index = [...]uint16{0, 4, 9, 19, 28, 33, 40, 49, 56, 63, 70, 78, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 220, 230, 238, 244, 253, 261, 268, 278, 286, 291, 300, 304, 313, 336, 343, 348, 360, 372, 389, 406, 415, 425, 433, 442, 452, 464, 475, 484, 496, 506, 515, 526, 535, 546}
+var _SymKind_index = [...]uint16{0, 4, 9, 19, 28, 33, 40, 49, 56, 63, 70, 78, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 220, 230, 238, 244, 253, 261, 268, 278, 286, 291, 300, 304, 313, 336, 353, 369, 376, 381, 393, 405, 422, 439, 448, 458, 466, 475, 485, 497, 508, 517, 529, 539, 548, 559, 568, 579}
 
 func (i SymKind) String() string {
 	if i >= SymKind(len(_SymKind_index)-1) {