On Wed, 2011-03-23 at 22:29 +0900, Namhyung Kim wrote:

The %pT format specifier is for stack backtrace. Its handler
sprint_trace() does symbol lookup using (address-1) to ensure
the address 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 pollutes call trace somewhat.
This patch will fix it.

before:
[   18.345923] Call Trace:
[   18.346001]  [<ffffffff812a8502>] panic+0x8c/0x18d
[   18.346257]  [<ffffffffa000012a>] deep01+0x0/0x38 [test_panic]  <--- bad
[   18.346347]  [<ffffffff81104666>] proc_file_write+0x73/0x8d
[   18.346432]  [<ffffffff811000b3>] proc_reg_write+0x8d/0xac
[   18.346516]  [<ffffffff810c7d32>] vfs_write+0xa1/0xc5
[   18.346603]  [<ffffffff810c7e0f>] sys_write+0x45/0x6c
[   18.346801]  [<ffffffff8f02943b>] system_call_fastpath+0x16/0x1b

after:
[   22.224483] Call Trace:
[   22.224569]  [<ffffffff812bce69>] panic+0x8c/0x18d
[   22.224848]  [<ffffffffa000012a>] panic_write+0x20/0x20 [test_panic]  <--- ok
[   22.224979]  [<ffffffff81115fab>] proc_file_write+0x73/0x8d
[   22.225089]  [<ffffffff81111a5f>] proc_reg_write+0x8d/0xac
[   22.225199]  [<ffffffff810d90ee>] vfs_write+0xa1/0xc5
[   22.225304]  [<ffffffff810d91cb>] sys_write+0x45/0x6c
[   22.225408]  [<ffffffff812c07fb>] system_call_fastpath+0x16/0x1b

Nice

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve