From bfc3b0f05653a28c8d41067a2aa3875d1f982e3e Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Sun, 9 Oct 2022 20:29:36 +0200 Subject: tools/nolibc: Fix missing strlen() definition and infinite loop with gcc-12 When built at -Os, gcc-12 recognizes an strlen() pattern in nolibc_strlen() and replaces it with a jump to strlen(), which is not defined as a symbol and breaks compilation. Worse, when the function is called strlen(), the function is simply replaced with a jump to itself, hence becomes an infinite loop. One way to avoid this is to always set -ffreestanding, but the calling code doesn't know this and there's no way (either via attributes or pragmas) to globally enable it from include files, effectively leaving a painful situation for the caller. Alexey suggested to place an empty asm() statement inside the loop to stop gcc from recognizing a well-known pattern, which happens to work pretty fine. At least it allows us to make sure our local definition is not replaced with a self jump. The function only needs to be renamed back to strlen() so that the symbol exists, which implies that nolibc_strlen() which is used on variable strings has to be declared as a macro that points back to it before the strlen() macro is redifined. It was verified to produce valid code with gcc 3.4 to 12.1 at different optimization levels, and both with constant and variable strings. In case this problem surfaces again in the future, an alternate approach consisting in adding an optimize("no-tree-loop-distribute-patterns") function attribute for gcc>=12 worked as well but is less pretty. Reported-by: kernel test robot Link: https://lore.kernel.org/r/202210081618.754a77db-yujie.liu@intel.com Fixes: 66b6f755ad45 ("rcutorture: Import a copy of nolibc") Fixes: 96980b833a21 ("tools/nolibc/string: do not use __builtin_strlen() at -O0") Cc: "Paul E. McKenney" Cc: Alexey Dobriyan Signed-off-by: Willy Tarreau Signed-off-by: Paul E. McKenney --- tools/include/nolibc/string.h | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) (limited to 'tools/include') diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h index bef35bee9c44..718a405ffbc3 100644 --- a/tools/include/nolibc/string.h +++ b/tools/include/nolibc/string.h @@ -125,14 +125,18 @@ char *strcpy(char *dst, const char *src) } /* this function is only used with arguments that are not constants or when - * it's not known because optimizations are disabled. + * it's not known because optimizations are disabled. Note that gcc 12 + * recognizes an strlen() pattern and replaces it with a jump to strlen(), + * thus itself, hence the asm() statement below that's meant to disable this + * confusing practice. */ static __attribute__((unused)) -size_t nolibc_strlen(const char *str) +size_t strlen(const char *str) { size_t len; - for (len = 0; str[len]; len++); + for (len = 0; str[len]; len++) + asm(""); return len; } @@ -140,13 +144,12 @@ size_t nolibc_strlen(const char *str) * the two branches, then will rely on an external definition of strlen(). */ #if defined(__OPTIMIZE__) +#define nolibc_strlen(x) strlen(x) #define strlen(str) ({ \ __builtin_constant_p((str)) ? \ __builtin_strlen((str)) : \ nolibc_strlen((str)); \ }) -#else -#define strlen(str) nolibc_strlen((str)) #endif static __attribute__((unused)) -- cgit v1.2.3 From b3f4f51ea68a495f8a5956064c33dce711a2df91 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Fri, 21 Oct 2022 08:01:53 +0200 Subject: tools/nolibc/string: Fix memcmp() implementation The C standard says that memcmp() must treat the buffers as consisting of "unsigned chars". If char happens to be unsigned, the casts are ok, but then obviously the c1 variable can never contain a negative value. And when char is signed, the casts are wrong, and there's still a problem with using an 8-bit quantity to hold the difference, because that can range from -255 to +255. For example, assuming char is signed, comparing two 1-byte buffers, one containing 0x00 and another 0x80, the current implementation would return -128 for both memcmp(a, b, 1) and memcmp(b, a, 1), whereas one of those should of course return something positive. Signed-off-by: Rasmus Villemoes Fixes: 66b6f755ad45 ("rcutorture: Import a copy of nolibc") Cc: stable@vger.kernel.org # v5.0+ Signed-off-by: Willy Tarreau Signed-off-by: Paul E. McKenney --- tools/include/nolibc/string.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'tools/include') diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h index 718a405ffbc3..ad97c0d522b8 100644 --- a/tools/include/nolibc/string.h +++ b/tools/include/nolibc/string.h @@ -19,9 +19,9 @@ static __attribute__((unused)) int memcmp(const void *s1, const void *s2, size_t n) { size_t ofs = 0; - char c1 = 0; + int c1 = 0; - while (ofs < n && !(c1 = ((char *)s1)[ofs] - ((char *)s2)[ofs])) { + while (ofs < n && !(c1 = ((unsigned char *)s1)[ofs] - ((unsigned char *)s2)[ofs])) { ofs++; } return c1; -- cgit v1.2.3 From a778f5d46b6287ebe26e24b48f3e8079c2db8ed2 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Wed, 2 Nov 2022 11:25:17 -0700 Subject: tools/headers: Pull in stddef.h to uapi to fix BPF selftests build in CI With recent sync of linux/in.h tools/include headers are now relying on __DECLARE_FLEX_ARRAY macro, which isn't itself defined inside tools/include headers anywhere and is instead assumed to be present in system-wide UAPI header. This breaks isolated environments that don't have kernel UAPI headers installed system-wide, like BPF CI ([0]). To fix this, bring in include/uapi/linux/stddef.h into tools/include. We can't just copy/paste it, though, it has to be processed with scripts/headers_install.sh, which has a dependency on scripts/unifdef. So the full command to (re-)generate stddef.h for inclusion into tools/include directory is: $ make scripts_unifdef && \ cp $KBUILD_OUTPUT/scripts/unifdef scripts/ && \ scripts/headers_install.sh include/uapi/linux/stddef.h tools/include/uapi/linux/stddef.h This assumes KBUILD_OUTPUT envvar is set and used for out-of-tree builds. [0] https://github.com/kernel-patches/bpf/actions/runs/3379432493/jobs/5610982609 Fixes: 036b8f5b8970 ("tools headers uapi: Update linux/in.h copy") Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Cc: Jakub Kicinski Cc: Arnaldo Carvalho de Melo Link: https://lore.kernel.org/bpf/20221102182517.2675301-2-andrii@kernel.org --- tools/include/uapi/linux/in.h | 1 + tools/include/uapi/linux/stddef.h | 47 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+) create mode 100644 tools/include/uapi/linux/stddef.h (limited to 'tools/include') diff --git a/tools/include/uapi/linux/in.h b/tools/include/uapi/linux/in.h index f243ce665f74..07a4cb149305 100644 --- a/tools/include/uapi/linux/in.h +++ b/tools/include/uapi/linux/in.h @@ -20,6 +20,7 @@ #define _UAPI_LINUX_IN_H #include +#include #include #include diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h new file mode 100644 index 000000000000..bb6ea517efb5 --- /dev/null +++ b/tools/include/uapi/linux/stddef.h @@ -0,0 +1,47 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _LINUX_STDDEF_H +#define _LINUX_STDDEF_H + + + +#ifndef __always_inline +#define __always_inline __inline__ +#endif + +/** + * __struct_group() - Create a mirrored named and anonyomous struct + * + * @TAG: The tag name for the named sub-struct (usually empty) + * @NAME: The identifier name of the mirrored sub-struct + * @ATTRS: Any struct attributes (usually empty) + * @MEMBERS: The member declarations for the mirrored structs + * + * Used to create an anonymous union of two structs with identical layout + * and size: one anonymous and one named. The former's members can be used + * normally without sub-struct naming, and the latter can be used to + * reason about the start, end, and size of the group of struct members. + * The named struct can also be explicitly tagged for layer reuse, as well + * as both having struct attributes appended. + */ +#define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \ + union { \ + struct { MEMBERS } ATTRS; \ + struct TAG { MEMBERS } ATTRS NAME; \ + } + +/** + * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union + * + * @TYPE: The type of each flexible array element + * @NAME: The name of the flexible array member + * + * In order to have a flexible array member in a union or alone in a + * struct, it needs to be wrapped in an anonymous struct with at least 1 + * named member, but that member can be empty. + */ +#define __DECLARE_FLEX_ARRAY(TYPE, NAME) \ + struct { \ + struct { } __empty_ ## NAME; \ + TYPE NAME[]; \ + } +#endif -- cgit v1.2.3