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Date: Mon, 18 Sep 2017 10:44:32 -0700 From: "Luck, Tony" <tony.luck@...el.com> To: Sergey Senozhatsky <sergey.senozhatsky@...il.com> Cc: Fenghua Yu <fenghua.yu@...el.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, "James E . J . Bottomley" <jejb@...isc-linux.org>, Helge Deller <deller@....de>, Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, Andrew Morton <akpm@...ux-foundation.org>, Jessica Yu <jeyu@...nel.org>, Alexei Starovoitov <ast@...nel.org>, linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 0/5] [RFC] printk/ia64/ppc64/parisc64: let's deprecate %pF/%pf printk specifiers On Sat, Sep 16, 2017 at 12:53:42PM +0900, Sergey Senozhatsky wrote: > Hello > > RFC > > On some arches C function pointers are indirect and point to > a function descriptor, which contains the actual pointer to the code. > This mostly doesn't matter, except for cases when people want to print > out function pointers in symbolic format, because the usual '%pS/%ps' > does not work on those arches as expected. That's the reason why we > have '%pF/%pf', but since it's here because of a subtle ABI detail > specific to some arches (ppc64/ia64/parisc64) it's easy to misuse > '%pF/%pf' and '%pS/%ps' (see [1], for example). A few new warnings when building on ia64: arch/ia64/kernel/module.c:931: warning: passing argument 1 of 'dereference_function_descriptor' makes pointer from integer without a cast arch/ia64/kernel/module.c:931: warning: return makes integer from pointer without a cast kernel/kallsyms.c:325: warning: assignment makes integer from pointer without a cast kernel/kallsyms.c:325: warning: passing argument 1 of 'dereference_kernel_function_descriptor' makes pointer from integer without a cast Tried out the module case with a simple Hello-world test case. This code: char buf[1]; int init_module(void) { printk(KERN_INFO "Hello world 1.\n"); printk("using %%p my init_module is at %p\n", init_module); printk("using %%pF my init_module is at %pF\n", init_module); printk("using %%pS my init_module is at %pS\n", init_module); printk("using %%p my buf is at %p\n", buf); printk("using %%pF my buf is at %pF\n", buf); printk("using %%pS my buf is at %pS\n", buf); return 0; } Gave this console output: Hello world 1. using %p my init_module is at a000000203bf0328 using %pF my init_module is at init_module+0x0/0x140 [hello_1] using %pS my init_module is at init_module+0x0/0x140 [hello_1] using %p my buf is at a000000203bf0648 using %pF my buf is at buf+0x0/0xfffffffffffffb58 [hello_1] using %pS my buf is at buf+0x0/0xfffffffffffffb58 [hello_1] Which looks like what you wanted. People unaware of the vagaries of ppc64/ia64/parisc64 can use the wrong %p[SF] variant, but still get the right output. -Tony
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