main: strip debug information at link time instead of at compile time

Stripping debug information at link time also allows relocation
compression (aka linker relaxations). Keeping debug information at
compile time and optionally stripping it at link time has some
advantages:

  * Automatic stack sizes on Cortex-M rely on the presence of debug
    information.
  * Some parts of the compiler now rely on the presence of debug
    information for proper diagnostics.
  * It works better with the cache: there is no distinction between
    debug and no-debug builds.
  * It makes it easier (or possible at all) to enable debug information
    in the wasi-libc library without big downsides.

builder/build.go

@@ -100,7 +100,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		AutomaticStackSize: config.AutomaticStackSize(),
 		DefaultStackSize:   config.Target.DefaultStackSize,
 		NeedsStackObjects:  config.NeedsStackObjects(),
-		Debug:              config.Debug(),
+		Debug:              true,
 		LLVMFeatures:       config.LLVMFeatures(),
 	}
 
@@ -539,6 +539,39 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		return fmt.Errorf("unknown libc: %s", config.Target.Libc)
 	}
 
+	// Strip debug information with -no-debug.
+	if !config.Debug() {
+		for _, tag := range config.BuildTags() {
+			if tag == "baremetal" {
+				// Don't use -no-debug on baremetal targets. It makes no sense:
+				// the debug information isn't flashed to the device anyway.
+				return fmt.Errorf("stripping debug information is unnecessary for baremetal targets")
+			}
+		}
+		if config.Target.Linker == "wasm-ld" {
+			// Don't just strip debug information, also compress relocations
+			// while we're at it. Relocations can only be compressed when debug
+			// information is stripped.
+			ldflags = append(ldflags, "--strip-debug", "--compress-relocations")
+		} else {
+			switch config.GOOS() {
+			case "linux":
+				// Either real linux or an embedded system (like AVR) that
+				// pretends to be Linux. It's a ELF linker wrapped by GCC in any
+				// case.
+				ldflags = append(ldflags, "-Wl,--strip-debug")
+			case "darwin":
+				// MacOS (darwin) doesn't have a linker flag to strip debug
+				// information. Apple expects you to use the strip command
+				// instead.
+				return errors.New("cannot remove debug information: MacOS doesn't suppor this linker flag")
+			default:
+				// Other OSes may have different flags.
+				return errors.New("cannot remove debug information: unknown OS: " + config.GOOS())
+			}
+		}
+	}
+
 	// Create a linker job, which links all object files together and does some
 	// extra stuff that can only be done after linking.
 	jobs = append(jobs, &compileJob{

compileopts/config.go

@@ -209,9 +209,8 @@ func (c *Config) CFlags() []string {
 		cflags = append(cflags, "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", filepath.Join(root, "lib", "picolibc", "newlib", "libc", "include"))
 		cflags = append(cflags, "-I"+filepath.Join(root, "lib/picolibc-include"))
 	}
-	if c.Debug() {
-		cflags = append(cflags, "-g")
-	}
+	// Always emit debug information. It is optionally stripped at link time.
+	cflags = append(cflags, "-g")
 	return cflags
 }
 
@@ -250,8 +249,9 @@ func (c *Config) VerifyIR() bool {
 	return c.Options.VerifyIR
 }
 
-// Debug returns whether to add debug symbols to the IR, for debugging with GDB
-// and similar.
+// Debug returns whether debug (DWARF) information should be retained by the
+// linker. By default, debug information is retained but it can be removed with
+// the -no-debug flag.
 func (c *Config) Debug() bool {
 	return c.Options.Debug
 }

main.go

@@ -1019,7 +1019,7 @@ func main() {
 	printStacks := flag.Bool("print-stacks", false, "print stack sizes of goroutines")
 	printAllocsString := flag.String("print-allocs", "", "regular expression of functions for which heap allocations should be printed")
 	printCommands := flag.Bool("x", false, "Print commands")
-	nodebug := flag.Bool("no-debug", false, "disable DWARF debug symbol generation")
+	nodebug := flag.Bool("no-debug", false, "strip debug information")
 	ocdCommandsString := flag.String("ocd-commands", "", "OpenOCD commands, overriding target spec (can specify multiple separated by commas)")
 	ocdOutput := flag.Bool("ocd-output", false, "print OCD daemon output during debug")
 	port := flag.String("port", "", "flash port (can specify multiple candidates separated by commas)")