From: George Guo <dongtai.guo@linux.dev>
To: gregkh@linuxfoundation.org, rostedt@goodmis.org,
mhiramat@kernel.org, tom.zanussi@linux.intel.com
Cc: stable@vger.kernel.org, Tom Zanussi <zanussi@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Joe Perches <joe@perches.com>,
Andreas Schwab <schwab@linux-m68k.org>,
George Guo <guodongtai@kylinos.cn>
Subject: [PATCH 4.19.y 06/13] string.h: Add str_has_prefix() helper function
Date: Thu, 9 May 2024 10:29:24 +0800 [thread overview]
Message-ID: <20240509022931.3513365-7-dongtai.guo@linux.dev> (raw)
In-Reply-To: <20240509022931.3513365-1-dongtai.guo@linux.dev>
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
commit 72921427d46bf9731a1ab7864adc64c43dfae29f upstream.
A discussion came up in the trace triggers thread about converting a
bunch of:
strncmp(str, "const", sizeof("const") - 1)
use cases into a helper macro. It started with:
strncmp(str, const, sizeof(const) - 1)
But then Joe Perches mentioned that if a const is not used, the
sizeof() will be the size of a pointer, which can be bad. And that
gcc will optimize strlen("const") into "sizeof("const") - 1".
Thinking about this more, a quick grep in the kernel tree found several
(thousands!) of cases that use this construct. A quick grep also
revealed that there's probably several bugs in that use case. Some are
that people forgot the "- 1" (which I found) and others could be that
the constant for the sizeof is different than the constant (although, I
haven't found any of those, but I also didn't look hard).
I figured the best thing to do is to create a helper macro and place it
into include/linux/string.h. And go around and fix all the open coded
versions of it later.
Note, gcc appears to optimize this when we make it into an always_inline
static function, which removes a lot of issues that a macro produces.
Link: http://lkml.kernel.org/r/e3e754f2bd18e56eaa8baf79bee619316ebf4cfc.1545161087.git.tom.zanussi@linux.intel.com
Link: http://lkml.kernel.org/r/20181219211615.2298e781@gandalf.local.home
Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Suggestions-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggestions-by: Joe Perches <joe@perches.com>
Suggestions-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
include/linux/string.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/include/linux/string.h b/include/linux/string.h
index 1e0c442b941e..f85860ab7e55 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -492,4 +492,24 @@ static inline void memcpy_and_pad(void *dest, size_t dest_len,
memcpy(dest, src, dest_len);
}
+/**
+ * str_has_prefix - Test if a string has a given prefix
+ * @str: The string to test
+ * @prefix: The string to see if @str starts with
+ *
+ * A common way to test a prefix of a string is to do:
+ * strncmp(str, prefix, sizeof(prefix) - 1)
+ *
+ * But this can lead to bugs due to typos, or if prefix is a pointer
+ * and not a constant. Instead use str_has_prefix().
+ *
+ * Returns: 0 if @str does not start with @prefix
+ strlen(@prefix) if @str does start with @prefix
+ */
+static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
+{
+ size_t len = strlen(prefix);
+ return strncmp(str, prefix, len) == 0 ? len : 0;
+}
+
#endif /* _LINUX_STRING_H_ */
--
2.34.1
next prev parent reply other threads:[~2024-05-09 2:30 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-09 2:29 [PATCH 4.19.y 00/13] fix double-free bug causing by destroy_hist_field(data->onmax.var, 0) George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 01/13] tracing: Simplify creation and deletion of synthetic events George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 02/13] tracing: Add unified dynamic event framework George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 03/13] tracing: Use dyn_event framework for synthetic events George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 04/13] tracing: Remove unneeded synth_event_mutex George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 05/13] tracing: Consolidate trace_add/remove_event_call back to the nolock functions George Guo
2024-05-09 2:29 ` George Guo [this message]
2024-05-09 2:29 ` [PATCH 4.19.y 07/13] tracing: Use str_has_prefix() helper for histogram code George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 08/13] tracing: Use str_has_prefix() instead of using fixed sizes George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 09/13] tracing: Have the historgram use the result of str_has_prefix() for len of prefix George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 10/13] tracing: Refactor hist trigger action code George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 11/13] tracing: Split up onmatch action data George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 12/13] tracing: Generalize hist trigger onmax and save action George Guo
2024-05-09 2:29 ` [PATCH 4.19.y 13/13] tracing: Remove unnecessary var_ref destroy in track_data_destroy() George Guo
2024-05-23 12:09 ` [PATCH 4.19.y 00/13] fix double-free bug causing by destroy_hist_field(data->onmax.var, 0) Greg KH
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