build: move link flags to build.rs

Binary-specific link flags (-nostartfiles, -static, section stripping)
now use cargo:rustc-link-arg-bin so they don't break proc-macro or
build-script linking. ld-wrapper only strips sections from static
binaries.

.cargo/config.toml

@@ -3,29 +3,14 @@
 # it as a post-link step.
 # See:
 #  <https://github.com/rui314/mold?tab=readme-ov-file#how-to-use>
+#
+# Binary-specific link flags live in microfetch/build.rs via cargo:rustc-link-arg-bin
+# so they only affect the final binary and don't break proc-macro or build-script linking.
 [target.'cfg(target_os = "linux")']
 linker = "scripts/ld-wrapper"
 rustflags = [
-  # No C runtime, we provide _start ourselves
-  "-C",
-  "link-arg=-nostartfiles",
-  # Fully static,  no dynamic linker, no .interp/.dynsym/.dynamic overhead
-  "-C",
-  "link-arg=-static",
-  # Static PIE is incompatible with -static :(
-  "-C",
-  "relocation-model=static",
   # Suppress .eh_frame emission from our own codegen (does not cover compiler_builtins;
   # those remnants are removed by the linker wrapper via objcopy post-link)
   "-C",
   "force-unwind-tables=no",
-  # Linker flags
-  "-C",
-  "link-arg=-Wl,--gc-sections",   # remove unreferenced input sections
-  "-C",
-  "link-arg=-Wl,--strip-all",     # strip all symbol table entries
-  "-C",
-  "link-arg=-Wl,--build-id=none", # omit the .note.gnu.build-id section
-  "-C",
-  "link-arg=-Wl,-z,norelro",      # disable RELRO (removes relro_padding)
 ]

microfetch/build.rs

@@ -0,0 +1,17 @@
+fn main() {
+  // These flags only apply to the microfetch binary, not to proc-macro crates
+  // or other host-compiled artifacts.
+
+  // No C runtime, we provide _start ourselves
+  println!("cargo:rustc-link-arg-bin=microfetch=-nostartfiles");
+  // Fully static, no dynamic linker, no .interp/.dynsym/.dynamic overhead
+  println!("cargo:rustc-link-arg-bin=microfetch=-static");
+  // Remove unreferenced input sections
+  println!("cargo:rustc-link-arg-bin=microfetch=-Wl,--gc-sections");
+  // Strip all symbol table entries
+  println!("cargo:rustc-link-arg-bin=microfetch=-Wl,--strip-all");
+  // Omit the .note.gnu.build-id section
+  println!("cargo:rustc-link-arg-bin=microfetch=-Wl,--build-id=none");
+  // Disable RELRO (removes relro_padding)
+  println!("cargo:rustc-link-arg-bin=microfetch=-Wl,-z,norelro");
+}

scripts/ld-wrapper

@@ -2,20 +2,23 @@
 # Invoke mold, then strip junk sections from the output binary with objcopy.
 # This (more or less) removes sections that mold cannot discard itself, suck as:
 #  - .eh_frame / .eh_frame_hdr  - unwind tables from compiler_builtins
-#  - dynstr                     - mold emits this, even for fully static binaries
+#  - .dynstr                     - mold emits this, even for fully static binaries
 #  - .comment                   - compiler version string
 #
 #  We forward everything to mold via -fuse-ld, then post-process the output in place.
 
 set -eu
 
-# Locate the output file
+# Locate the output file and detect static linking
+IS_STATIC=0
 OUTPUT=""
 prev=""
 for arg in "$@"; do
+	case "$arg" in
+		-static) IS_STATIC=1 ;;
+	esac
 	if [ "$prev" = "-o" ]; then
 		OUTPUT="$arg"
-		break
 	fi
 	prev="$arg"
 done
@@ -23,8 +26,9 @@ done
 # Invoke mold via the cc driver, forward all original arguments
 cc -fuse-ld=mold "$@"
 
-# Remove sections that mold cannot discard
-if [ -n "$OUTPUT" ] && [ -f "$OUTPUT" ]; then
+# Only strip sections from fully static binaries.
+# Dynamic executables (i.e. build scripts, proc-macros) need .dynstr at runtime.
+if [ "$IS_STATIC" = 1 ] && [ -n "$OUTPUT" ] && [ -f "$OUTPUT" ]; then
 	objcopy \
 		--remove-section=.eh_frame \
 		--remove-section=.eh_frame_hdr \