On 15.08.2017 14:46, Steven Rostedt wrote:
> On Thu, 10 Aug 2017 19:35:33 +0200
> Helge Deller <deller@xxxxxx> wrote:
>
>> Sometimes people seems unclear when to use the %pS or %pF printk format.
>> Adding some examples may help to avoid such mistakes.
>>
>> See for example commit 51d96dc2e2dc ("random: fix warning message on ia64 and
>> parisc") which fixed such a wrong format string.
>>
>> Signed-off-by: Helge Deller <deller@xxxxxx>
>>
>> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
>> index 65ea591..be8c05b 100644
>> --- a/Documentation/printk-formats.txt
>> +++ b/Documentation/printk-formats.txt
>> @@ -73,6 +73,12 @@ actually function descriptors which must first be resolved. The ``F`` and
>> ``f`` specifiers perform this resolution and then provide the same
>> functionality as the ``S`` and ``s`` specifiers.
>>
>> +Examples::
>> +
>> + printk("Called from %pS.\n", __builtin_return_address(0));
>> + printk("Called from %pS.\n", (void *)regs->ip);
>> + printk("Called from %pF.\n", &gettimeofday);
>
> Is the '&' really necessary?
The '&' is not necessary. The compiler doesn't complain either.
> What about using the example:
> printk("Called in %pF.\n", __func__);
Very interesting!
This code:
void smp_cpus_done() {
printk("Called from %pF.\n", smp_cpus_done);
printk("Called from %pf.\n", smp_cpus_done);
printk("Called in %pS.\n", __func__);
printk("Called in %ps.\n", __func__);
printk("Called in %pF.\n", __func__);
printk("Called in %pf.\n", __func__);
gives:
Called from smp_cpus_done+0x0/0x1b8.
Called from smp_cpus_done.
Called in __func__.28197+0x0/0x20.
Called in __func__.28197.
Called in 0x5041524953433332.
Called in 0x5041524953433332.
So, the correct usage is:
printk("Called in %pS.\n", __func__);
But it should have printed
Called from smp_cpus_done+0x0/0x1b8.
which means the (parisc?) printk resolver doesn't work correctly.
In assembly code a pointer to this object is handed to printk:
.type __func__.28197, @object
.size __func__.28197, 14
__func__.28197:
.stringz "smp_cpus_done"
I'll look into this problem.
Helge
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