| Message ID | 20171109234830.5067-6-sergey.senozhatsky@gmail.com (mailing list archive) |
|---|---|
| State | Awaiting Upstream, archived |
| Headers | show |
On Fri, Nov 10, 2017 at 08:48:29AM +0900, Sergey Senozhatsky wrote: > -Examples:: > - > - printk("Going to call: %pF\n", gettimeofday); > - printk("Going to call: %pF\n", p->func); > - 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); > - printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); Did you mean to delete the Examples completely? Wouldn't it be better to just update (s/%pF/%pS/g)? -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On (11/10/17 10:09), Luck, Tony wrote: > On Fri, Nov 10, 2017 at 08:48:29AM +0900, Sergey Senozhatsky wrote: > > -Examples:: > > - > > - printk("Going to call: %pF\n", gettimeofday); > > - printk("Going to call: %pF\n", p->func); > > - 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); > > - printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); > > Did you mean to delete the Examples completely? Wouldn't it > be better to just update (s/%pF/%pS/g)? good question. yes, I think I did it deliberately :) we still kinda have some sort of "examples", right at the beginning of section "Symbols/Function Pointers" > Symbols/Function Pointers > ========================= > > :: > > %pS versatile_init+0x0/0x110 > %ps versatile_init > %pF versatile_init+0x0/0x110 > %pf versatile_init > %pSR versatile_init+0x9/0x110 > (with __builtin_extract_return_addr() translation) > %pB prev_fn_of_versatile_init+0x88/0x88 > > The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic > format. They result in the symbol name with (``S``) or without (``s``) > offsets. If KALLSYMS are disabled then the symbol address is printed instead. > > Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``) > and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and > parisc64 function pointers are indirect and, in fact, are function > descriptors, which require additional dereferencing before we can lookup > the symbol. As of now, ``S`` and ``s`` perform dereferencing on those > platforms (when needed), so ``F`` and ``f`` exist for compatibility > reasons only. > > The ``B`` specifier results in the symbol name with offsets and should be > used when printing stack backtraces. The specifier takes into > consideration the effect of compiler optimisations which may occur > when tail-call``s are used and marked with the noreturn GCC attribute. I can return Examples back. don't really have a strong opinion on this. let me know. -ss -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat 2017-11-11 13:49:32, Sergey Senozhatsky wrote: > On (11/10/17 10:09), Luck, Tony wrote: > > On Fri, Nov 10, 2017 at 08:48:29AM +0900, Sergey Senozhatsky wrote: > > > -Examples:: > > > - > > > - printk("Going to call: %pF\n", gettimeofday); > > > - printk("Going to call: %pF\n", p->func); > > > - 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); > > > - printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); > > > > Did you mean to delete the Examples completely? Wouldn't it > > be better to just update (s/%pF/%pS/g)? > > good question. yes, I think I did it deliberately :) we still > kinda have some sort of "examples", right at the beginning of > section "Symbols/Function Pointers" These extra examples were added just recently (v4.14-rc1) by the commit fd46cd55fbc5a8e8c ("printk-formats.txt: Add examples for %pF and %pS usage"). They were supposed to help using %pF and %pS correctly according to the situation. But we have a better solution now. %pF is obsoleted by this patchset. IMHO, it is perfectly fine to remove the extra examples. Best Regards, Petr -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt index 361789df51ec..2f17e684b72e 100644 --- a/Documentation/printk-formats.txt +++ b/Documentation/printk-formats.txt @@ -50,42 +50,31 @@ Symbols/Function Pointers :: - %pF versatile_init+0x0/0x110 - %pf versatile_init - %pS versatile_init+0x0/0x110 - %pSR versatile_init+0x9/0x110 - (with __builtin_extract_return_addr() translation) - %ps versatile_init - %pB prev_fn_of_versatile_init+0x88/0x88 - -The ``F`` and ``f`` specifiers are for printing function pointers, -for example, f->func, &gettimeofday. They have the same result as -``S`` and ``s`` specifiers. But they do an extra conversion on -ia64, ppc64 and parisc64 architectures where the function pointers -are actually function descriptors. - -The ``S`` and ``s`` specifiers can be used for printing symbols -from direct addresses, for example, __builtin_return_address(0), -(void *)regs->ip. They result in the symbol name with (``S``) or -without (``s``) offsets. If KALLSYMS are disabled then the symbol -address is printed instead. + %pS versatile_init+0x0/0x110 + %ps versatile_init + %pF versatile_init+0x0/0x110 + %pf versatile_init + %pSR versatile_init+0x9/0x110 + (with __builtin_extract_return_addr() translation) + %pB prev_fn_of_versatile_init+0x88/0x88 + +The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic +format. They result in the symbol name with (``S``) or without (``s``) +offsets. If KALLSYMS are disabled then the symbol address is printed instead. + +Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``) +and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and +parisc64 function pointers are indirect and, in fact, are function +descriptors, which require additional dereferencing before we can lookup +the symbol. As of now, ``S`` and ``s`` perform dereferencing on those +platforms (when needed), so ``F`` and ``f`` exist for compatibility +reasons only. The ``B`` specifier results in the symbol name with offsets and should be used when printing stack backtraces. The specifier takes into consideration the effect of compiler optimisations which may occur when tail-call``s are used and marked with the noreturn GCC attribute. -Examples:: - - printk("Going to call: %pF\n", gettimeofday); - printk("Going to call: %pF\n", p->func); - 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); - printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); - - Kernel Pointers =============== diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h index 11dd93e42580..73f7e874c3e1 100644 --- a/include/linux/kallsyms.h +++ b/include/linux/kallsyms.h @@ -16,6 +16,8 @@ struct module; +void *dereference_symbol_descriptor(void *ptr); + #ifdef CONFIG_KALLSYMS /* Lookup the address for a symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name); diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 1966fe1c2b57..18b3dffc4b84 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -411,6 +411,25 @@ static int __sprint_symbol(char *buffer, unsigned long address, return len; } +void *dereference_symbol_descriptor(void *ptr) +{ +#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR + struct module *mod; + + ptr = dereference_kernel_function_descriptor(ptr); + if (is_ksym_addr((unsigned long)ptr)) + return ptr; + + preempt_disable(); + mod = __module_address((unsigned long)ptr); + preempt_enable(); + + if (mod) + ptr = dereference_module_function_descriptor(mod, ptr); +#endif + return ptr; +} + /** * sprint_symbol - Look up a kernel symbol and return it in a text buffer * @buffer: buffer to be stored diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 1746bae94d41..16e2eefb0f79 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -40,7 +40,6 @@ #include "../mm/internal.h" /* For the trace_print_flags arrays */ #include <asm/page.h> /* for PAGE_SIZE */ -#include <asm/sections.h> /* for dereference_function_descriptor() */ #include <asm/byteorder.h> /* cpu_to_le16 */ #include <linux/string_helpers.h> @@ -1723,10 +1722,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, switch (*fmt) { case 'F': case 'f': - ptr = dereference_function_descriptor(ptr); - /* Fallthrough */ case 'S': case 's': + ptr = dereference_symbol_descriptor(ptr); + /* Fallthrough */ case 'B': return symbol_string(buf, end, ptr, spec, fmt); case 'R':
dereference_symbol_descriptor() invokes appropriate ARCH specific function descriptor dereference callbacks: - dereference_kernel_function_descriptor() if the pointer is a kernel symbol; - dereference_module_function_descriptor() if the pointer is a module symbol. This is the last step needed to make '%pS/%ps' smart enough to handle function descriptor dereference on affected ARCHs and to retire '%pF/%pf'. To refresh it: Some architectures (ia64, ppc64, parisc64) use an indirect pointer for C function pointers - the function pointer points to a function descriptor and we need to dereference it to get the actual function pointer. Function descriptors live in .opd elf section and all affected ARCHs (ia64, ppc64, parisc64) handle it properly for kernel and modules. So we, technically, can decide if the dereference is needed by simply looking at the pointer: if it belongs to .opd section then we need to dereference it. The kernel and modules have their own .opd sections, obviously, that's why we need to split dereference_function_descriptor() and use separate kernel and module dereference arch callbacks. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- Documentation/printk-formats.txt | 49 ++++++++++++++++------------------------ include/linux/kallsyms.h | 2 ++ kernel/kallsyms.c | 19 ++++++++++++++++ lib/vsprintf.c | 5 ++-- 4 files changed, 42 insertions(+), 33 deletions(-)