[RFC PATCH] Allow annotating calloc for Valgrind

[Alexander Monakov <amonakov@ispras.ru>]

With mal0_clear entered only for larger-than-one-page allocations, a
few additional nops and stack accesses don't matter.

This only needs Valgrind headers to build, Valgrind itself doesn't need to be
built/installed.  However, valgrind.h unconditionally includes stdarg.h.

Untested.
---
 configure           | 11 +++++++++++
 src/malloc/malloc.c |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/configure b/configure
index c2db298c..7e78094f 100755
--- a/configure
+++ b/configure
@@ -30,6 +30,7 @@ System types:
 Optional features:
   --enable-optimize=...   optimize listed components for speed over size [auto]
   --enable-debug          build with debugging information [disabled]
+  --enable-valgrind       add Valgrind annotations [disabled]
   --enable-warnings       build with recommended warnings flags [disabled]
   --enable-visibility     use global visibility options to optimize PIC [auto]
   --enable-wrapper=...    build given musl toolchain wrapper [auto]
@@ -134,6 +135,7 @@ build=
 target=
 optimize=auto
 debug=no
+valgrind=no
 warnings=no
 visibility=auto
 shared=auto
@@ -161,6 +163,8 @@ case "$arg" in
 --disable-optimize) optimize=no ;;
 --enable-debug|--enable-debug=yes) debug=yes ;;
 --disable-debug|--enable-debug=no) debug=no ;;
+--enable-valgrind|--enable-valgrind=yes) valgrind=yes ;;
+--disable-valgrind|--enable-valgrind=no) valgrind=no ;;
 --enable-warnings|--enable-warnings=yes) warnings=yes ;;
 --disable-warnings|--enable-warnings=no) warnings=no ;;
 --enable-visibility|--enable-visibility=yes) visibility=yes ;;
@@ -390,6 +394,13 @@ tryflag CFLAGS_MEMOPS -fno-tree-loop-distribute-patterns
 #
 test "$debug" = yes && CFLAGS_AUTO=-g
 
+if test x"$valgrind" = xyes  ; then
+CPPFLAGS="$CPPFLAGS -DVG_MEMCHECK_H='<memcheck.h>'"
+else
+CPPFLAGS="$CPPFLAGS -DVG_MEMCHECK_H='</dev/null>'"
+fi
+CPPFLAGS="${CPPFLAGS# }"
+
 #
 # Preprocess asm files to add extra debugging information if debug is
 # enabled, our assembler supports the needed directives, and the
diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index b56fdaa2..d4c229bd 100644
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -8,6 +8,7 @@
 #include "libc.h"
 #include "atomic.h"
 #include "pthread_impl.h"
+#include VG_MEMCHECK_H
 
 #if defined(__GNUC__) && defined(__PIC__)
 #define inline inline __attribute__((always_inline))
@@ -373,6 +374,9 @@ static size_t mal0_clear(char *p, size_t pagesz, size_t n)
 	typedef unsigned long long T;
 	char *pp = p + n;
 	size_t i = (uintptr_t)pp & (pagesz - 1);
+#ifdef VALGRIND_MAKE_MEM_DEFINED_IF_ADDRESSABLE
+	VALGRIND_MAKE_MEM_DEFINED_IF_ADDRESSABLE(p, n);
+#endif
 	for (;;) {
 		pp = memset(pp - i, 0, i);
 		if (pp - p < pagesz) return pp - p;
-- 
2.11.0