New string function explicit_bzero (from OpenBSD).

explicit_bzero(s, n) is the same as memset(s, 0, n), except that the
compiler is not allowed to delete a call to explicit_bzero even if the
memory pointed to by 's' is dead after the call.  Right now, this effect
is achieved externally by having explicit_bzero be a function whose
semantics are unknown to the compiler, and internally, with a no-op
asm statement that clobbers memory.  This does mean that small
explicit_bzero operations cannot be expanded inline as small memset
operations can, but on the other hand, small memset operations do get
deleted by the compiler.  Hopefully full compiler support for
explicit_bzero will happen relatively soon.

There are two new tests: test-explicit_bzero.c verifies the
visible semantics in the same way as the existing test-bzero.c,
and tst-xbzero-opt.c verifies the not-being-optimized-out property.
The latter is conceptually based on a test written by Matthew Dempsky
for the OpenBSD regression suite.

The crypt() implementation has an immediate use for this new feature.
We avoid having to add a GLIBC_PRIVATE alias for explicit_bzero
by running all of libcrypt's calls through the fortified variant,
__explicit_bzero_chk, which is in the impl namespace anyway.  Currently
I'm not aware of anything in libc proper that needs this, but the
glue is all in place if it does become necessary.  The legacy DES
implementation wasn't bothering to clear its buffers, so I added that,
mostly for consistency's sake.

	* string/explicit_bzero.c: New routine.
	* string/test-explicit_bzero.c, string/tst-xbzero-opt.c: New tests.
	* string/Makefile (routines, strop-tests, tests): Add them.
	* string/test-memset.c: Add ifdeffage for testing explicit_bzero.
	* string/string.h [__USE_MISC]: Declare explicit_bzero.

	* debug/explicit_bzero_chk.c: New routine.
	* debug/Makefile (routines): Add it.
	* debug/tst-chk1.c: Test fortification of explicit_bzero.
	* string/bits/string3.h: Fortify explicit_bzero.

	* manual/string.texi: Document explicit_bzero.
	* NEWS: Mention addition of explicit_bzero.

	* crypt/crypt-entry.c (__crypt_r): Clear key-dependent intermediate
	data before returning, using explicit_bzero.
	* crypt/md5-crypt.c (__md5_crypt_r): Likewise.
	* crypt/sha256-crypt.c (__sha256_crypt_r): Likewise.
	* crypt/sha512-crypt.c (__sha512_crypt_r): Likewise.

	* include/string.h: Redirect internal uses of explicit_bzero
	to __explicit_bzero_chk[_internal].
	* string/Versions [GLIBC_2.25]: Add explicit_bzero.
	* debug/Versions [GLIBC_2.25]: Add __explicit_bzero_chk.
	* sysdeps/arm/nacl/libc.abilist
	* sysdeps/unix/sysv/linux/aarch64/libc.abilist
	* sysdeps/unix/sysv/linux/alpha/libc.abilist
	* sysdeps/unix/sysv/linux/arm/libc.abilist
	* sysdeps/unix/sysv/linux/hppa/libc.abilist
	* sysdeps/unix/sysv/linux/i386/libc.abilist
	* sysdeps/unix/sysv/linux/ia64/libc.abilist
	* sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
	* sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
	* sysdeps/unix/sysv/linux/microblaze/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
	* sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist
	* sysdeps/unix/sysv/linux/nios2/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist
	* sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist
	* sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist
	* sysdeps/unix/sysv/linux/sh/libc.abilist
	* sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist
	* sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist
	* sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist
	* sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
	* sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist:
	Add entries for explicit_bzero and __explicit_bzero_chk.

1 files changed, 4 insertions, 3 deletions

diff --git a/string/Makefile b/string/Makefile
index 69d3f802fb..9a8b46d1bf 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -41,20 +41,21 @@ routines	:= strcat strchr strcmp strcoll strcpy strcspn		\
 				     addsep replace)			\
 		   envz basename					\
 		   strcoll_l strxfrm_l string-inlines memrchr		\
-		   xpg-strerror strerror_l
+		   xpg-strerror strerror_l explicit_bzero
 
 strop-tests	:= memchr memcmp memcpy memmove mempcpy memset memccpy	\
 		   stpcpy stpncpy strcat strchr strcmp strcpy strcspn	\
 		   strlen strncmp strncpy strpbrk strrchr strspn memmem	\
 		   strstr strcasestr strnlen strcasecmp strncasecmp	\
-		   strncat rawmemchr strchrnul bcopy bzero memrchr
+		   strncat rawmemchr strchrnul bcopy bzero memrchr	\
+		   explicit_bzero
 tests		:= tester inl-tester noinl-tester testcopy test-ffs	\
 		   tst-strlen stratcliff tst-svc tst-inlcall		\
 		   bug-strncat1 bug-strspn1 bug-strpbrk1 tst-bswap	\
 		   tst-strtok tst-strxfrm bug-strcoll1 tst-strfry	\
 		   bug-strtok1 $(addprefix test-,$(strop-tests))	\
 		   bug-envz1 tst-strxfrm2 tst-endian tst-svc2		\
-		   tst-strtok_r bug-strcoll2 tst-cmp
+		   tst-strtok_r bug-strcoll2 tst-cmp tst-xbzero-opt
 
 xtests = tst-strcoll-overflow