cmd/link, runtime: use a different section for Go libfuzzer counters

Currently in libfuzzer mode, we put our counters in section
__sancov_cntrs. When linking with C/C++ code that also has fuzzer
counters, apparently the C linker combines our counters and their
counters and registers them together. But in the Go runtime we
also have code to register our counters. So the Go counters ended
up registered twice, causing problems.

Since we already have code to register our counters, put them in
a Go-specific section so it won't be combined with the C counters.

Fixes #57449.

Change-Id: If3d41735124e7e301572d4b7aecf7d057ac134c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/459055
Reviewed-by: Nicolas Hillegeer <aktau@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>

src/cmd/link/internal/ld/data.go

@@ -1860,9 +1860,9 @@ func (state *dodataState) allocateDataSections(ctxt *Link) {
 
 	// 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)
-		ldr.SetSymSect(ldr.LookupOrCreateSym("__start___sancov_cntrs", 0), sect)
-		ldr.SetSymSect(ldr.LookupOrCreateSym("__stop___sancov_cntrs", 0), sect)
+		sect := state.allocateNamedSectionAndAssignSyms(&Segdata, ".go.fuzzcntrs", sym.SLIBFUZZER_8BIT_COUNTER, sym.Sxxx, 06)
+		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.__start___sancov_cntrs", 0), sect)
+		ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.__stop___sancov_cntrs", 0), sect)
 		ldr.SetSymSect(ldr.LookupOrCreateSym("internal/fuzz._counters", 0), sect)
 		ldr.SetSymSect(ldr.LookupOrCreateSym("internal/fuzz._ecounters", 0), sect)
 	}
@@ -2643,7 +2643,7 @@ func (ctxt *Link) address() []*sym.Segment {
 			bss = s
 		case ".noptrbss":
 			noptrbss = s
-		case "__sancov_cntrs":
+		case ".go.fuzzcntrs":
 			fuzzCounters = s
 		}
 	}
@@ -2764,8 +2764,8 @@ func (ctxt *Link) address() []*sym.Segment {
 	ctxt.xdefine("runtime.end", sym.SBSS, int64(Segdata.Vaddr+Segdata.Length))
 
 	if fuzzCounters != nil {
-		ctxt.xdefine("__start___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
-		ctxt.xdefine("__stop___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
+		ctxt.xdefine("runtime.__start___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
+		ctxt.xdefine("runtime.__stop___sancov_cntrs", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
 		ctxt.xdefine("internal/fuzz._counters", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr))
 		ctxt.xdefine("internal/fuzz._ecounters", sym.SLIBFUZZER_8BIT_COUNTER, int64(fuzzCounters.Vaddr+fuzzCounters.Length))
 	}

src/cmd/link/internal/ld/elf.go

@@ -1371,7 +1371,7 @@ func (ctxt *Link) doelf() {
 	shstrtab.Addstring(".data")
 	shstrtab.Addstring(".bss")
 	shstrtab.Addstring(".noptrbss")
-	shstrtab.Addstring("__sancov_cntrs")
+	shstrtab.Addstring(".go.fuzzcntrs")
 	shstrtab.Addstring(".go.buildinfo")
 	if ctxt.IsMIPS() {
 		shstrtab.Addstring(".MIPS.abiflags")

src/runtime/libfuzzer.go

@@ -148,13 +148,8 @@ var __sanitizer_cov_trace_const_cmp8 byte
 //go:cgo_import_static __sanitizer_cov_8bit_counters_init
 var __sanitizer_cov_8bit_counters_init byte
 
-//go:linkname __start___sancov_cntrs __start___sancov_cntrs
-//go:cgo_import_static __start___sancov_cntrs
-var __start___sancov_cntrs byte
-
-//go:linkname __stop___sancov_cntrs __stop___sancov_cntrs
-//go:cgo_import_static __stop___sancov_cntrs
-var __stop___sancov_cntrs byte
+// start, stop markers of counters, set by the linker
+var __start___sancov_cntrs, __stop___sancov_cntrs byte
 
 //go:linkname __sanitizer_cov_pcs_init __sanitizer_cov_pcs_init
 //go:cgo_import_static __sanitizer_cov_pcs_init