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    Subject[PATCH] add a printk_init variant storing format strings in __initdata
    Date

    [As gcc seems unable to help us out selecting the appropriate data segment
    for the code, how about we did something like this?]

    When using printk from __init functions it would be desirable to place
    the printk format strings in __initdata. Add a printk_init() variant
    which does this.

    This printk_init() is necessarily a #define so that we can declare the
    format string in static scope and mark it __initdata. We then call a
    newly introduced __printk_init() variant which is identicle to printk() but
    marked __init itself. By ensuring that an __init variant of printk is used
    we get proper section violation warnings when this is used incorrectly:

    WARNING: vmlinux.o(.text+0x3): Section mismatch in reference from the
    function something() to the variable .init.data:__printk_init_fmt.31426
    The function something() references
    the variable __initdata __printk_init_fmt.31426.
    This is often because something lacks a __initdata
    annotation or the annotation of __printk_init_fmt.31426 is wrong.

    Note I have followed printk's pattern for __cold annotations.

    Signed-off-by: Andy Whitcroft <apw@shadowen.org>
    ---
    include/linux/kernel.h | 10 ++++++++++
    kernel/printk.c | 12 ++++++++++++
    2 files changed, 22 insertions(+), 0 deletions(-)
    diff --git a/include/linux/kernel.h b/include/linux/kernel.h
    index 792bf0a..7754196 100644
    --- a/include/linux/kernel.h
    +++ b/include/linux/kernel.h
    @@ -180,6 +180,13 @@ struct pid;
    extern struct pid *session_of_pgrp(struct pid *pgrp);

    #ifdef CONFIG_PRINTK
    +#define printk_init(fmt, args...) \
    +do { \
    + static char __printk_init_fmt[] __initdata = fmt; \
    + __printk_init(__printk_init_fmt, ##args); \
    +} while (0)
    +asmlinkage int __printk_init(const char * fmt, ...)
    + __attribute__ ((format (printf, 1, 2))) __cold;
    asmlinkage int vprintk(const char *fmt, va_list args)
    __attribute__ ((format (printf, 1, 0)));
    asmlinkage int printk(const char * fmt, ...)
    @@ -196,6 +203,9 @@ extern int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst);
    extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
    unsigned int interval_msec);
    #else
    +asmlinkage int printk_init(const char * fmt, ...)
    + __attribute__ ((format (printf, 1, 2))) __cold;
    +static inline int __cold printk_init(const char *s, ...) { return 0; }
    static inline int vprintk(const char *s, va_list args)
    __attribute__ ((format (printf, 1, 0)));
    static inline int vprintk(const char *s, va_list args) { return 0; }
    diff --git a/kernel/printk.c b/kernel/printk.c
    index 8fb01c3..992a5c0 100644
    --- a/kernel/printk.c
    +++ b/kernel/printk.c
    @@ -616,6 +616,18 @@ asmlinkage int printk(const char *fmt, ...)
    return r;
    }

    +asmlinkage __init int __printk_init(const char *fmt, ...)
    +{
    + va_list args;
    + int r;
    +
    + va_start(args, fmt);
    + r = vprintk(fmt, args);
    + va_end(args);
    +
    + return r;
    +}
    +
    /* cpu currently holding logbuf_lock */
    static volatile unsigned int printk_cpu = UINT_MAX;


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