fix(bench): separate vlibc-under-test TU from host harness TUs

benchmarks/bench_vlibc.c

@@ -5,16 +5,29 @@
  * This stub times vlibc_version() and is the skeleton that per-component
  * benchmarks build on. Reconfigure with --with-libc=musl or --with-libc=glibc
  * to link the same harness against a reference libc for comparison.
+ *
+ * This TU is deliberately a HOST-headers-only translation unit: it includes
+ * no vlibc header, because vlibc's self-contained
+ * <stdarg.h>/<stddef.h>/<limits.h>/<float.h> shadow GCC's internal headers
+ * and mixing them with the system <stdio.h>/<time.h> hard-errors. The
+ * function under test is reached through the adapter TU
+ * bench_vlibc_under.c, which is compiled with vlibc's headers and exposes
+ * the call through its own declaration here.
  */
 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif
 
-#include <vlibc.h>
-
 #include <stdio.h>
 #include <time.h>
 
+/* Adapter entry (bench_vlibc_under.c); declared here rather than including
+ * <vlibc.h>, which this host-header TU must not do. The adapter also drops
+ * vlibc_version()'s __attribute__((const)), so the timed loop really
+ * executes the call. */
+const char *
+bench_vlibc_version(void);
+
 #define ITERATIONS 100000000ULL
 
 int
@@ -34,7 +47,7 @@ main(void)
 
     for (unsigned long long i = 0; i < ITERATIONS; i++)
     {
-        version = vlibc_version();
+        version = bench_vlibc_version();
     }
 
     if (clock_gettime(CLOCK_MONOTONIC, &end) != 0)
@@ -49,5 +62,13 @@ main(void)
     printf("vlibc_version() x %llu: %.3f s (%.2f ns/call), version=%s\n", ITERATIONS, seconds,
            seconds * 1000000000.0 / ITERATIONS, (const char *)version);
 
+    /*
+     * Explicit flush: this harness is a host program, but its DT_NEEDED order
+     * puts libvlibc.so before libc.so.6, so the exit() that runs at process
+     * end is vlibc's — which does not flush stdio yet (that hook lands with
+     * the stdio todo). Without the flush the buffered result above is lost.
+     */
+    fflush(stdout);
+
     return 0;
 }