From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Namhyung Kim <namhyung@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Joe Perches <joe@perches.com>, Tom Zanussi <zanussi@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro
Date: Fri, 21 Dec 2018 15:55:13 -0500 [thread overview]
Message-ID: <20181221155513.11450ca6@gandalf.local.home> (raw)
In-Reply-To: <CAHk-=wjtkvFUuRNZU67KccuUKYHw=pYoDMQJ_9OVDFxOwmK9zQ@mail.gmail.com>
On Fri, 21 Dec 2018 12:41:17 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Parentheses....
?
-- Steve
>
> On Fri, Dec 21, 2018, 12:35 Steven Rostedt <rostedt@goodmis.org wrote:
>
> > On Fri, 21 Dec 2018 12:01:48 -0800
> > Linus Torvalds <torvalds@linux-foundation.org> wrote:
> >
> > > On Fri, Dec 21, 2018 at 11:40 AM Steven Rostedt <rostedt@goodmis.org>
> > wrote:
> > > >
> > > > OK, what about if we just use strlen() and say that this macro is not
> > > > safe for parameters with side effects.
> > >
> > > I think gcc follows simple assignments just fine, and does the
> > > optimized strlen() for them too.
> > >
> > > So why not just do
> > >
> > > #define have_prefix(str,prefix) ({ \
> > > const char *__pfx = prefix; \
> > > size_t __pfxlen = strlen(__pfx); \
> > > strncmp(str, __pfx, __pfxlen) ? 0 : __pfxlen); })
> > >
> > > and be done with it safely?
> > >
> > > The above is ENTIRELY untested.
> > >
> >
> > At first I thought this would have issues, but with a slight change...
> >
> > #define have_prefix(str, prefix) ({ \
> > const char *__pfx = (const char *)prefix; \
> >
> >
> > And the rest the same, it appears to work.
> >
> > Need the cast because if for some reason someone passed in something
> > like "const unsigned char" then it wouldn't work. But that's just a nit.
> >
> > So something like this then?
> >
> > -- Steve
> >
> > diff --git a/include/linux/string.h b/include/linux/string.h
> > index 27d0482e5e05..4586fee60194 100644
> > --- a/include/linux/string.h
> > +++ b/include/linux/string.h
> > @@ -14,6 +14,28 @@ extern void *memdup_user(const void __user *, size_t);
> > extern void *vmemdup_user(const void __user *, size_t);
> > extern void *memdup_user_nul(const void __user *, size_t);
> >
> > +/**
> > + * have_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 has_prefix().
> > + *
> > + * Returns: 0 if @str does not start with @prefix
> > + strlen(@prefix) if @str does start with @prefix
> > + */
> > +#define has_prefix(str, prefix)
> > \
> > + ({ \
> > + const char *____prefix____ = (const char *)(prefix); \
> > + int ____len____ = strlen(____prefix____); \
> > + strncmp(str, ____prefix____, ____len____) == 0 ? \
> > + ____len____ : 0; \
> > + })
> > +
> > /*
> > * Include machine specific inline routines
> > */
> >
next prev parent reply other threads:[~2018-12-21 20:55 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-21 17:56 [for-next][PATCH 00/24] tracing: Updates for the next (coming soon) merge window Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 01/24] ftrace: Allow ftrace_replace_code() to be schedulable Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 02/24] arm64: ftrace: Set FTRACE_MAY_SLEEP before ftrace_modify_all_code() Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 03/24] fgraph: Add comment to describe ftrace_graph_get_ret_stack Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 04/24] x86/ftrace: Do not call function graph from dynamic trampolines Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 05/24] powerpc/frace: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack Steven Rostedt
2018-12-22 9:51 ` Michael Ellerman
2018-12-22 12:24 ` Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 06/24] sparc64: " Steven Rostedt
2018-12-21 18:24 ` David Miller
2018-12-21 19:29 ` Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 07/24] sh: ftrace: " Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 08/24] arm64: " Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 10/24] seq_buf: Use size_t for len in seq_buf_puts() Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 11/24] tracing: Fix ftrace_graph_get_ret_stack() to use task and not current Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 12/24] tracing: Remove unnecessary hist trigger struct field Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 13/24] tracing: Change strlen to sizeof for hist trigger static strings Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 14/24] tracing: Use var_refs[] for hist trigger reference checking Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 15/24] tracing: Remove open-coding of hist trigger var_ref management Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 16/24] tracing: Use hist triggers var_ref array to destroy var_refs Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 17/24] tracing: Remove hist trigger synth_var_refs Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 18/24] tracing: Add hist trigger comments for variable-related fields Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 19/24] tracing: Merge seq_print_sym_short() and seq_print_sym_offset() Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 21/24] tracing: Simplify printfing in seq_print_sym Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro Steven Rostedt
2018-12-21 18:51 ` Linus Torvalds
2018-12-21 19:40 ` Steven Rostedt
2018-12-21 20:01 ` Linus Torvalds
2018-12-21 20:35 ` Steven Rostedt
2018-12-21 20:46 ` Joe Perches
2018-12-21 20:54 ` Steven Rostedt
2018-12-21 20:58 ` Andreas Schwab
2018-12-21 21:08 ` Steven Rostedt
2018-12-21 22:20 ` Joe Perches
2018-12-21 22:29 ` Linus Torvalds
2018-12-21 22:58 ` Steven Rostedt
2018-12-21 22:55 ` Steven Rostedt
2018-12-23 22:01 ` Rasmus Villemoes
2018-12-23 22:56 ` Steven Rostedt
2018-12-23 23:52 ` Rasmus Villemoes
2018-12-24 0:05 ` Steven Rostedt
2018-12-23 23:01 ` Joe Perches
2018-12-21 20:58 ` Steven Rostedt
[not found] ` <CAHk-=wjtkvFUuRNZU67KccuUKYHw=pYoDMQJ_9OVDFxOwmK9zQ@mail.gmail.com>
2018-12-21 20:55 ` Steven Rostedt [this message]
2018-12-21 22:08 ` Linus Torvalds
2018-12-21 22:48 ` Steven Rostedt
2018-12-21 22:57 ` Linus Torvalds
2018-12-21 23:03 ` Steven Rostedt
2018-12-22 10:20 ` Malcolm Priestley
2018-12-22 12:26 ` Steven Rostedt
2018-12-21 17:56 ` [for-next][PATCH 24/24] tracing: Use strncmp_prefix() helper for histogram code Steven Rostedt
[not found] ` <20181221175656.827708767@goodmis.org>
2018-12-21 18:00 ` [for-next][PATCH 09/24] seq_buf: Make seq_buf_puts() null-terminate the buffer Steven Rostedt
2018-12-21 18:05 ` Steven Rostedt
2018-12-27 5:25 ` Michael Ellerman
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