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

benchmarks/Makefile.am

@@ -10,18 +10,30 @@ EXTRA_PROGRAMS = bench_vlibc bench_string
 bench_vlibc_SOURCES = bench_vlibc.c
 bench_string_SOURCES = bench_string.c
 
-# bench_string is a system-headers-only translation unit (it times whichever
-# libc it is linked against), so it must NOT inherit AM_CPPFLAGS: -I include
-# would pull vlibc's self-contained <stddef.h>/<string.h> into the same TU as
-# the system <stdio.h>/<time.h> and double-define size_t/NULL/offsetof.
-# bench_vlibc keeps the inherited -I include.
+# Both harness TUs are system-headers-only translation units (they time
+# whichever libc they are linked against), so they must NOT inherit
+# AM_CPPFLAGS: -I include would pull vlibc's self-contained
+# <stdarg.h>/<stddef.h>/<string.h> into the same TU as the system
+# <stdio.h>/<time.h> and double-define size_t/NULL/offsetof (or hide the
+# compiler's internal <stdarg.h> behind vlibc's). The vlibc function under
+# test is reached through the adapter TU bench_vlibc_under.c, which is
+# compiled with vlibc's headers and exposes the call to the harness through
+# its own declaration (see that file).
+bench_vlibc_CPPFLAGS =
 bench_string_CPPFLAGS =
 
+# Adapter TU for bench_vlibc: vlibc's headers only, so it must NOT inherit
+# the (empty) per-target CPPFLAGS above; it gets the include path back
+# explicitly.
+bench_vlibc_under.o: bench_vlibc_under.c
+	$(AM_V_CC)$(CC) -I$(top_srcdir)/include $(CPPFLAGS) $(AM_CFLAGS) \
+	    $(CFLAGS) -c -o $@ $<
+
 # By default benchmarks link against vlibc itself. --with-libc=glibc links the
 # same harness against the system glibc; --with-libc=musl builds it with
 # musl-gcc for the musl reference.
 if BENCH_LINK_VLIBC
-bench_vlibc_LDADD = ../libvlibc.la
+bench_vlibc_LDADD = bench_vlibc_under.o ../libvlibc.la
 bench_string_LDADD = ../libvlibc.la
 else
 bench_vlibc_LDADD =
@@ -38,6 +50,12 @@ endif
 # binary from the previous configuration and the wrong libc would be measured.
 EXTRA_bench_string_DEPENDENCIES = $(top_builddir)/config.status
 EXTRA_bench_vlibc_DEPENDENCIES = $(top_builddir)/config.status
+bench_vlibc_DEPENDENCIES = bench_vlibc_under.o
+
+# The adapter TU is built by a hand-rolled rule (per-TU include paths), so it
+# is not picked up by automake's automatic distribution/cleaning.
+EXTRA_DIST = bench_vlibc_under.c
+CLEANFILES = bench_vlibc_under.o
 
 # bench_vlibc.c calls vlibc_version(), which exists only in vlibc — under
 # --with-libc=glibc/musl it cannot link, so it is built and run only in the

benchmarks/bench_string.c

@@ -149,5 +149,14 @@ main(void)
         printf("%llu\n", sink);
     }
 
+    /*
+     * Explicit flush: this harness is a host program, but under
+     * --with-libc=vlibc 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 timed results above are lost.
+     */
+    fflush(stdout);
+
     return 0;
 }

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;
 }

benchmarks/bench_vlibc_under.c

@@ -0,0 +1,29 @@
+/*
+ * vlibc-under-test adapter for the bench_vlibc harness (todo 6 bench fix).
+ *
+ * This translation unit is compiled with vlibc's OWN headers (-I ../include)
+ * and is the ONLY TU in the benchmark that may include a vlibc header. The
+ * harness TU (bench_vlibc.c) must never include one: vlibc's self-contained
+ * <stdarg.h>/<stddef.h>/<limits.h>/<float.h> shadow GCC's internal headers,
+ * so any TU that mixes a vlibc header with the host <stdio.h>/<time.h>
+ * fails to compile (glibc's <stdio.h> needs __gnuc_va_list, which only the
+ * compiler's internal <stdarg.h> defines). The adapter isolates the
+ * vlibc-facing call here and exposes it to the host-header harness through
+ * its own declaration.
+ *
+ * Passing through the adapter also drops vlibc_version()'s
+ * __attribute__((const)) at the harness call site: the harness sees a plain
+ * external function, so the timed loop genuinely executes the call instead
+ * of being hoisted out by the optimizer.
+ */
+
+#include <vlibc.h>
+
+const char *
+bench_vlibc_version(void);
+
+const char *
+bench_vlibc_version(void)
+{
+    return vlibc_version();
+}