From 95d78c7e7c81a6b788f28c33ef2cafd87471a0d7 Mon Sep 17 00:00:00 2001

From: David Herrmann <dh.herrmann@gmail.com>

Date: Mon, 22 Sep 2014 12:05:16 +0200

Subject: [PATCH] util: add alloca_align()

The alloca_align() helper is the alloca() equivalent of posix_memalign().

As there is no such function provided by glibc, we simply account for

additional memory and return a pointer offset into the allocated memory to

grant the alignment.

Furthermore, alloca0_align() is added, which simply clears the allocated

memory.

---

 src/shared/util.h    | 16 ++++++++++++++++

 src/test/test-util.c | 14 ++++++++++++++

 2 files changed, 30 insertions(+)

diff --git a/src/shared/util.h b/src/shared/util.h

index 08d556fc92..a1d5657237 100644

--- a/src/shared/util.h

+++ b/src/shared/util.h

@@ -852,6 +852,22 @@ int unlink_noerrno(const char *path);

                 (void *) memset(_new_, 0, _len_);       \

         })

+#define alloca_align(size, align)                                       \

+        ({                                                              \

+                void *_ptr_;                                            \

+                size_t _mask_ = (align) - 1;                            \

+                _ptr_ = alloca((size) + _mask_);                        \

+                (void*)(((uintptr_t)_ptr_ + _mask_) & ~_mask_);         \

+        })

+

+#define alloca0_align(size, align)                                      \

+        ({                                                              \

+                void *_new_;                                            \

+                size_t _size_ = (size);                                 \

+                _new_ = alloca_align(_size_, (align));                  \

+                (void*)memset(_new_, 0, _size_);                        \

+        })

+

 #define strappenda(a, ...)                                       \

         ({                                                       \

                 int _len = strlen(a);                            \

diff --git a/src/test/test-util.c b/src/test/test-util.c

index f8e42f3a55..1311184815 100644

--- a/src/test/test-util.c

+++ b/src/test/test-util.c

@@ -131,6 +131,19 @@ static void test_container_of(void) {

                                v1) == &myval);

 }

+static void test_alloca(void) {

+        static const uint8_t zero[997] = { };

+        char *t;

+

+        t = alloca_align(17, 512);

+        assert_se(!((uintptr_t)t & 0xff));

+        memzero(t, 17);

+

+        t = alloca0_align(997, 1024);

+        assert_se(!((uintptr_t)t & 0x1ff));

+        assert_se(!memcmp(t, zero, 997));

+}

+

 static void test_first_word(void) {

         assert_se(first_word("Hello", ""));

         assert_se(first_word("Hello", "Hello"));

@@ -1272,6 +1285,7 @@ int main(int argc, char *argv[]) {

         test_align_power2();

         test_max();

         test_container_of();

+        test_alloca();

         test_first_word();

         test_close_many();

         test_parse_boolean();