linux-kernel - Re: [patch for 2.6.26 0/7] Architecture Independent Markers

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Date:	Fri, 28 Mar 2008 01:01:29 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch for 2.6.26 0/7] Architecture Independent Markers

On Thursday 27 March 2008 14:20, Mathieu Desnoyers wrote:
> Hi Andrew,
> 
> After a few RFC rounds, I propose these markers for 2.6.26. They include
> work done after comments from the memory management community. Most of them have
> been used by the LTTng project for about 2 years.

Not in this patch, but I noticed:

#define __trace_mark(name, call_private, format, args...)               \
        do {                                                            \
                static const char __mstrtab_##name[]                    \
                __attribute__((section("__markers_strings")))           \
                = #name "\0" format;                                    \
                static struct marker __mark_##name                      \
                __attribute__((section("__markers"), aligned(8))) =     \
                { __mstrtab_##name, &__mstrtab_##name[sizeof(#name)],   \
                0, 0, marker_probe_cb,                                  \
                { __mark_empty_function, NULL}, NULL };                 \
                __mark_check_format(format, ## args);                   \
                if (unlikely(__mark_##name.state)) {                    \
                        (*__mark_##name.call)                           \
                                (&__mark_##name, call_private,          \
                                format, ## args);                       \
                }                                                       \
        } while (0)

In this call:

                        (*__mark_##name.call)                           \
                                (&__mark_##name, call_private,          \
                                format, ## args);                       \

you make gcc allocate duplicate format string. You can use
&__mstrtab_##name[sizeof(#name)] instead since it holds the same string,
or drop ", format," above and "const char *fmt" from here:

        void (*call)(const struct marker *mdata,        /* Probe wrapper */
                void *call_private, const char *fmt, ...);

since mdata->format is the same and all callees which need it can take it there.
--
vda
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