cmd/link: fix cgo on riscv64 when building with gcc-15

It's not currently possible to build cgo programs that are partially
compiled with gcc-15 on riscv64 using the internal linker. There are
two reasons for this.

1. When gcc-15 compiles _cgo_export.c, which contains no actual code,
   for a riscv64 target, it emits a label in the .text section called
   .Letext0. This label is referred to by another section, .debug_line,
   and an entry is generated in the symbol table for it. The Go linker
   panics when processing the .Letext0 symbol in _cgo_export.o, as it
   occurs in an empty section.
2. GCC-15 is generating additional debug symbols with the .LVUS
   prefix, e.g., .LVUS33, that need to be ignored.

We fix the issue by removing the check in
cmd/link/internal/loader/loader.go that panics if we encounter a
symbol in an empty section (the comments preceding this check suggest
it's safe to remove it) and by adding .LVUS to the list of symbol
prefixes to ignore.

Fixes #72840

Change-Id: I00658b6bdd01606dde1581b5bc2f42edfc37de82
Reviewed-on: https://go-review.googlesource.com/c/go/+/668276
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>

diff --git a/src/cmd/link/internal/loadelf/ldelf.go b/src/cmd/link/internal/loadelf/ldelf.go
index e0363b5535ccea3568007e5b0f606103431576e4..9f251e746b79adf162964e25f495d0982887119f 100644 (file)
--- a/src/cmd/link/internal/loadelf/ldelf.go
+++ b/src/cmd/link/internal/loadelf/ldelf.go
@@ -609,7 +609,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
                                continue
                        }
 
-                       if strings.HasPrefix(elfsym.name, ".LASF") || strings.HasPrefix(elfsym.name, ".LLRL") || strings.HasPrefix(elfsym.name, ".LLST") {
+                       if strings.HasPrefix(elfsym.name, ".LASF") || strings.HasPrefix(elfsym.name, ".LLRL") || strings.HasPrefix(elfsym.name, ".LLST") || strings.HasPrefix(elfsym.name, ".LVUS") {
                                // gcc on s390x and riscv64 does this.
                                continue
                        }

diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 6a7057b80e81eaa1b2ee6121791c7553c0f5344d..128173b8cf990c5dabb94c394173dd5be526bcec 100644 (file)
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -1719,14 +1719,6 @@ func (l *Loader) GetVarDwarfAuxSym(i Sym) Sym {
 // expected to have the actual content/payload) and then a set of
 // interior loader.Sym's that point into a portion of the container.
 func (l *Loader) AddInteriorSym(container Sym, interior Sym) {
-       // Container symbols are expected to have content/data.
-       // NB: this restriction may turn out to be too strict (it's possible
-       // to imagine a zero-sized container with an interior symbol pointing
-       // into it); it's ok to relax or remove it if we counter an
-       // oddball host object that triggers this.
-       if l.SymSize(container) == 0 && len(l.Data(container)) == 0 {
-               panic("unexpected empty container symbol")
-       }
        // The interior symbols for a container are not expected to have
        // content/data or relocations.
        if len(l.Data(interior)) != 0 {