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    SubjectRe: [PATCH 00/14] Fix wrong %pF and %pS printk format specifier usages
    On (09/08/17 20:28), Helge Deller wrote:
    [..]
    > I don't like this kind of trying to figure out at runtime at all.
    > It's too much guessing in here IMHO.

    well, may be we can avoid any guessing by checking that the
    pointer belongs to .opd section.

    for kernel we can add 2 new unsigned longs - __opd_start __opd_end -- and
    tweak the corresponding arch/${FOO}/kernel/vmlinux.lds.S file to set those
    two, the same way text, unwinding, etc. are set.

    .... wait a second.

    arch/ia64/kernel/vmlinux.lds.S already handles .opd section

    .opd : AT(ADDR(.opd) - LOAD_OFFSET) {
    *(.opd)
    }

    it just doesn't save start/end addresses. so all we need to to
    is

    .opd : AT(ADDR(.opd) - LOAD_OFFSET) {
    + __opd_start = .;
    *(.opd)
    + __opd_end = .;
    }

    and tweak symbol dereference

    static inline void *dereference_function_descriptor(void *ptr)
    {
    struct fdesc *desc = ptr;
    void *p;

    + if (prt < (void *)__start_opd || (void *)__end_opd < ptr)
    + return ptr;
    +
    if (!probe_kernel_address(&desc->ip, p))
    ptr = p;
    return ptr;



    now, the modules.

    module_frob_arch_sections() has the following lines

    else if (strcmp(".opd", secstrings + s->sh_name) == 0)
    mod->arch.opd = s;

    so, once, again, we keep the .opd section info in memory. and we
    also have the size of that section

    mod->arch.opd->sh_size = fdescs * sizeof(struct fdesc);

    so it seems that we've got what we need. need to provide arch callback
    (same way as we do with dereference_function_descriptor() to properly
    dereference modules' symbols).


    so I think we almost have what we need to make ps/pS smart enough
    on ppc64/ia64/parisc.

    powerpc and parisc handle kernel .opd section as well:

    arch/powerpc/kernel/vmlinux.lds.S: .opd
    arch/parisc/kernel/vmlinux.lds.S: .opd


    need to check more.


    > What about this idea:
    > For %pF we always have pointers to functions, e.g.:
    > printk("Going to call: %pF\n", gettimeofday);
    > printk("Going to call: %pF\n", p->func);
    >
    > and for %pS most (if not all) usages use some kind of casting
    > from "unsigned long" to "void *", e.g.:
    > printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
    > printk("%s: called from %pS\n", __func__, (void *)__builtin_return_address(0));
    > printk("Faulted at %pS\n", (void *)regs->ip);
    >
    > So, what if we for the %pS case simply take the type as it is
    > (unsigned long) and introduce a new printk-format, e.g. "%luS" ?
    > The %pS examples above then become:
    > printk("%s: called from %luS\n", __func__, _RET_IP_);
    > printk("%s: called from %luS\n", __func__, __builtin_return_address(0));
    > printk("Faulted at %luS\n", regs->ip);
    >
    > That way we don't need type-casting, gain compile-time type
    > checks from the compiler, and we could add a checkpatch (or occinelle)
    > check which checks for the combination of %pF/%pS and "void*" keyword
    > and suggest to use %luS.
    >
    > Opinions?

    hm. sounds interesting. but I'm afraid people won't be so happy
    to learn a new printk format specifier.

    -ss

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