[V4][0/2] explicit_bzero

[V4][0/2] explicit_bzero

[roucaries.bastien]

Sorry for the late reply

Last modification of explicit_bzero

[PATCH 1/2] Support clang for explicit_bzero

[roucaries.bastien]

From: Bastien Roucariès <rouca@debian.org>

According to https://bugs.llvm.org/show_bug.cgi?id=15495#c11
llvm need g type constraint

Signed-off-by: Bastien Roucariès <rouca@debian.org>
---
 lib/explicit_bzero.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
index 87fadba81a..71a1cca3b0 100644
--- a/lib/explicit_bzero.c
+++ b/lib/explicit_bzero.c
@@ -56,9 +56,19 @@ explicit_bzero (void *s, size_t len)
   (void) memset_s (s, len, '\0', len);
 #else
   memset (s, '\0', len);
-# if defined __GNUC__ && !defined __clang__
-  /* Compiler barrier.  */
+# if defined __GNUC__
+/* Compiler barrier.  */
+#  if !defined __clang__
   asm volatile ("" ::: "memory");
+#  else
+   /* See https://bugs.llvm.org/show_bug.cgi?id=15495#c11
+      with asm("" ::: "memory") LLVM analyzes uses of 's'
+      and finds that the whole thing is dead and eliminates it.
+
+      Using g workarround this problem
+   */
+  __asm__ volatile("" : : "g"(s) : "memory");
+#  endif
 # endif
 #endif
 }
-- 
2.29.2

[PATCH 2/2] Implement fallback for explicit_bzero using jump to volatile pointer

[roucaries.bastien]

From: Bastien Roucariès <rouca@debian.org>

Signed-off-by: Bastien Roucariès <rouca@debian.org>
---
 lib/explicit_bzero.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
index 71a1cca3b0..86a5fd35d7 100644
--- a/lib/explicit_bzero.c
+++ b/lib/explicit_bzero.c
@@ -54,11 +54,10 @@ explicit_bzero (void *s, size_t len)
   explicit_memset (s, '\0', len);
 #elif HAVE_MEMSET_S
   (void) memset_s (s, len, '\0', len);
-#else
+#elif defined __GNUC__
   memset (s, '\0', len);
-# if defined __GNUC__
 /* Compiler barrier.  */
-#  if !defined __clang__
+# if !defined __clang__
   asm volatile ("" ::: "memory");
 #  else
    /* See https://bugs.llvm.org/show_bug.cgi?id=15495#c11
@@ -70,5 +69,8 @@ explicit_bzero (void *s, size_t len)
   __asm__ volatile("" : : "g"(s) : "memory");
 #  endif
 # endif
+#else
+  void * (* const volatile volatile_memset)(void *, int, size_t) = memset;
+  (void) volatile_memset(s, '\0', len);
 #endif
 }
-- 
2.29.2

[PATCH 1/2] Support clang for explicit_bzero

[roucaries.bastien]

From: Bastien Roucariès <rouca@debian.org>

According to https://bugs.llvm.org/show_bug.cgi?id=15495#c11
llvm need g type constraint

Signed-off-by: Bastien Roucariès <rouca@debian.org>
---
 lib/explicit_bzero.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
index 87fadba81a..71a1cca3b0 100644
--- a/lib/explicit_bzero.c
+++ b/lib/explicit_bzero.c
@@ -56,9 +56,19 @@ explicit_bzero (void *s, size_t len)
   (void) memset_s (s, len, '\0', len);
 #else
   memset (s, '\0', len);
-# if defined __GNUC__ && !defined __clang__
-  /* Compiler barrier.  */
+# if defined __GNUC__
+/* Compiler barrier.  */
+#  if !defined __clang__
   asm volatile ("" ::: "memory");
+#  else
+   /* See https://bugs.llvm.org/show_bug.cgi?id=15495#c11
+      with asm("" ::: "memory") LLVM analyzes uses of 's'
+      and finds that the whole thing is dead and eliminates it.
+
+      Using g workarround this problem
+   */
+  __asm__ volatile("" : : "g"(s) : "memory");
+#  endif
 # endif
 #endif
 }
-- 
2.29.2

Re: [PATCH 1/2] Support clang for explicit_bzero

[Bruno Haible]

> diff --git a/lib/explicit_bzero.c b/lib/explicit_bzero.c
> index 87fadba81a..71a1cca3b0 100644
> --- a/lib/explicit_bzero.c
> +++ b/lib/explicit_bzero.c
> @@ -56,9 +56,19 @@ explicit_bzero (void *s, size_t len)
>    (void) memset_s (s, len, '\0', len);
>  #else
>    memset (s, '\0', len);
> -# if defined __GNUC__ && !defined __clang__
> -  /* Compiler barrier.  */
> +# if defined __GNUC__
> +/* Compiler barrier.  */
> +#  if !defined __clang__
>    asm volatile ("" ::: "memory");
> +#  else
> +   /* See https://bugs.llvm.org/show_bug.cgi?id=15495#c11
> +      with asm("" ::: "memory") LLVM analyzes uses of 's'
> +      and finds that the whole thing is dead and eliminates it.
> +
> +      Using g workarround this problem
> +   */
> +  __asm__ volatile("" : : "g"(s) : "memory");
> +#  endif
>  # endif
>  #endif
>  }

Thanks. I applied this with two changes:
  - Make it work also with clang on Windows. Recall that clang on Windows
    does not define __GNUC__ [1].
  - Use a gnulib-style ChangeLog entry.

Bruno

[1] https://lists.gnu.org/archive/html/bug-gnulib/2020-08/msg00038.html