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Date: Fri, 18 Mar 2011 11:27:55 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Namhyung Kim <namhyung@...il.com>
Cc: linux-kernel@...r.kernel.org,
Frederic Weisbecker <fweisbec@...il.com>,
Jason Wessel <jason.wessel@...driver.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC 1/2] vsprintf: introduce %pT format specifier
On Fri, Mar 18, 2011 at 08:21:17PM +0900, Namhyung Kim wrote:
> The %pT format specifier is for stack backtrace. Its handler
> sprint_trace() does symbol lookup using (offset-1) to ensure
> the offset will not point outside of the function.
>
> If there is a tail-call to the function marked "noreturn",
> gcc optimized out the code after the call then causes saved
> return address points outside of the function (i.e. the start
> of the next function), so messes up a call trace entry.
> This patch will fix it.
This looks uselful.
> kernel/kallsyms.c | 26 ++++++++++++++++++++++++++
> lib/vsprintf.c | 7 ++++++-
> 3 files changed, 39 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
> index d8e9b3d1c23c..4964ed2021cc 100644
> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -36,6 +36,7 @@ const char *kallsyms_lookup(unsigned long addr,
>
> /* Look up a kernel symbol and return it in a text buffer. */
> extern int sprint_symbol(char *buffer, unsigned long address);
> +extern int sprint_trace(char *buffer, unsigned long address);
>
> /* Look up a kernel symbol and print it to the kernel messages. */
> extern void __print_symbol(const char *fmt, unsigned long address);
> @@ -79,6 +80,12 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
> return 0;
> }
>
> +static inline int sprint_trace(char *buffer, unsigned long addr)
> +{
> + *buffer = '\0';
> + return 0;
> +}
> +
> static inline int lookup_symbol_name(unsigned long addr, char *symname)
> {
> return -ERANGE;
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 6f6d091b5757..2e43200cdc79 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -368,6 +368,32 @@ int sprint_symbol(char *buffer, unsigned long address)
> }
> EXPORT_SYMBOL_GPL(sprint_symbol);
>
This desperately needs a comment. Please add a kernel doc style header
to this. (ie.:)
/**
* sprint_trace - one line description
* @buffer: what is the buffer
* @address: what is the address
*
* describe why this function exists and how to use it.
*
* Returns: what are the return values.
*/
-- Steve
> +int sprint_trace(char *buffer, unsigned long address)
> +{
> + char *modname;
> + const char *name;
> + unsigned long offset, size;
> + int len;
> +
> + name = kallsyms_lookup(address-1, &size, &offset, &modname, buffer);
> + if (!name)
> + return sprintf(buffer, "0x%lx", address);
> +
> + if (name != buffer)
> + strcpy(buffer, name);
> + len = strlen(buffer);
> + buffer += len;
> + offset++;
> +
> + if (modname)
> + len += sprintf(buffer, "+%#lx/%#lx [%s]",
> + offset, size, modname);
> + else
> + len += sprintf(buffer, "+%#lx/%#lx", offset, size);
> +
> + return len;
> +}
> +
> /* Look up a kernel symbol and print it to the kernel messages. */
> void __print_symbol(const char *fmt, unsigned long address)
> {
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index d3023df8477f..c9c56a54cc42 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -574,7 +574,9 @@ char *symbol_string(char *buf, char *end, void *ptr,
> unsigned long value = (unsigned long) ptr;
> #ifdef CONFIG_KALLSYMS
> char sym[KSYM_SYMBOL_LEN];
> - if (ext != 'f' && ext != 's')
> + if (ext == 'T')
> + sprint_trace(sym, value);
> + else if (ext != 'f' && ext != 's')
> sprint_symbol(sym, value);
> else
> kallsyms_lookup(value, NULL, NULL, NULL, sym);
> @@ -949,6 +951,7 @@ int kptr_restrict = 1;
> * - 'f' For simple symbolic function names without offset
> * - 'S' For symbolic direct pointers with offset
> * - 's' For symbolic direct pointers without offset
> + * - 'T' For backtraced symbolic direct pointers with offset
> * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
> * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]
> * - 'M' For a 6-byte MAC address, it prints the address in the
> @@ -1008,6 +1011,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> /* Fallthrough */
> case 'S':
> case 's':
> + case 'T':
> return symbol_string(buf, end, ptr, spec, *fmt);
> case 'R':
> case 'r':
> @@ -1279,6 +1283,7 @@ qualifier:
> * %ps output the name of a text symbol without offset
> * %pF output the name of a function pointer with its offset
> * %pf output the name of a function pointer without its offset
> + * %pT output the name of a trace symbol with its offset
> * %pR output the address range in a struct resource with decoded flags
> * %pr output the address range in a struct resource with raw flags
> * %pM output a 6-byte MAC address with colons
> --
> 1.7.4
>
> --
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