The dwarf unwinder ties in to an early initcall, but it's possible that
return_address() calls will be made prior to that. This implements some
additional error handling in to the dwarf unwinder as well as an exit
path in the return_address() case to bail out if the unwinder hasn't come
up yet.
This fixes a NULL pointer deref in early boot when mempool_alloc() blows
up on the not-yet-ready mempool via dwarf_unwind_stack().
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Previously the struct module definition was pulled in from other headers,
but we want the reference to be explicit. Fixes up randconfig build
issues.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files. percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.
percpu.h -> slab.h dependency is about to be removed. Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability. As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.
http://userweb.kernel.org/~tj/misc/slabh-sweep.py
The script does the followings.
* Scan files for gfp and slab usages and update includes such that
only the necessary includes are there. ie. if only gfp is used,
gfp.h, if slab is used, slab.h.
* When the script inserts a new include, it looks at the include
blocks and try to put the new include such that its order conforms
to its surrounding. It's put in the include block which contains
core kernel includes, in the same order that the rest are ordered -
alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
doesn't seem to be any matching order.
* If the script can't find a place to put a new include (mostly
because the file doesn't have fitting include block), it prints out
an error message indicating which .h file needs to be added to the
file.
The conversion was done in the following steps.
1. The initial automatic conversion of all .c files updated slightly
over 4000 files, deleting around 700 includes and adding ~480 gfp.h
and ~3000 slab.h inclusions. The script emitted errors for ~400
files.
2. Each error was manually checked. Some didn't need the inclusion,
some needed manual addition while adding it to implementation .h or
embedding .c file was more appropriate for others. This step added
inclusions to around 150 files.
3. The script was run again and the output was compared to the edits
from #2 to make sure no file was left behind.
4. Several build tests were done and a couple of problems were fixed.
e.g. lib/decompress_*.c used malloc/free() wrappers around slab
APIs requiring slab.h to be added manually.
5. The script was run on all .h files but without automatically
editing them as sprinkling gfp.h and slab.h inclusions around .h
files could easily lead to inclusion dependency hell. Most gfp.h
inclusion directives were ignored as stuff from gfp.h was usually
wildly available and often used in preprocessor macros. Each
slab.h inclusion directive was examined and added manually as
necessary.
6. percpu.h was updated not to include slab.h.
7. Build test were done on the following configurations and failures
were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my
distributed build env didn't work with gcov compiles) and a few
more options had to be turned off depending on archs to make things
build (like ipr on powerpc/64 which failed due to missing writeq).
* x86 and x86_64 UP and SMP allmodconfig and a custom test config.
* powerpc and powerpc64 SMP allmodconfig
* sparc and sparc64 SMP allmodconfig
* ia64 SMP allmodconfig
* s390 SMP allmodconfig
* alpha SMP allmodconfig
* um on x86_64 SMP allmodconfig
8. percpu.h modifications were reverted so that it could be applied as
a separate patch and serve as bisection point.
Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
The parent rb_node needs to be initialized to shut up the compiler, even
though we're unlikely to ever hit this issue at run time.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Now that the DWARF unwinder is being used to provide perf callstacks
unwinding speed is an issue. It is no longer being used in exceptional
circumstances where we don't care about runtime performance, e.g. when
panicing, so it makes sense improve performance is possible.
With this patch I saw a 42% improvement in unwind time when calling
return_address(1). Greater improvements will be seen as the number of
levels unwound increases as each unwind is now cheaper.
Note that insertion time has doubled but that's just the price we pay
for keeping the trees balanced. However, this is a one-time cost for
kernel boot/module load and so the improvements in lookup time dominate
the extra time we spend keeping the trees balanced.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Unfortunately, due to poor DWARF info in current toolchains, unwinding
through interrutps cannot be done reliably. The problem is that the
DWARF info for function epilogues is wrong.
Take this standard epilogue sequence,
80003cc4: e3 6f mov r14,r15
80003cc6: 26 4f lds.l @r15+,pr
80003cc8: f6 6e mov.l @r15+,r14
<---- interrupt here
80003cca: f6 6b mov.l @r15+,r11
80003ccc: f6 6a mov.l @r15+,r10
80003cce: f6 69 mov.l @r15+,r9
80003cd0: 0b 00 rts
If we take an interrupt at the highlighted point, the DWARF info will
bogusly claim that the return address can be found at some offset from
the frame pointer, even though the frame pointer was just restored. The
worst part is if the unwinder finds a text address at the bogus stack
address - unwinding will continue, for a bit, until it finally comes
across an unexpected address on the stack and blows up.
The only solution is to stop unwinding once we've calculated the
function that was executing when the interrupt occurred. This PC can be
easily calculated from pt_regs->pc.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
The dwarf unwinder presently attempts to provide a sane PC value if none
is provided, however the logic is broken and cases where a previous valid
dwarf frame exists along with a bogus PC value can still proceed. This
fixes up the test and prevents the unwinder from blowing up.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
When CONFIG_FUNCTION_GRAPH_TRACER is enabled the function graph tracer
may patch return addresses on the stack with the address of
return_to_handler(). This really confuses the DWARF unwinder because it
will try find the caller of return_to_handler(), not the caller of the
real return address.
So teach the DWARF unwinder how to find the real return address whenever
it encounters return_to_handler().
This patch does not cope very well when multiple return addresses on the
stack have been patched. To make it work properly it would require state
to track how many return_to_handler()'s have been seen so that we'd know
where to look in current->curr_ret_stack[]. So for now, instead of
trying to handle this, just moan if more than one return address on the
stack has been patched.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This enables us to build the dwarf unwinder both with modules enabled and
disabled in addition to reducing code size in the latter case. The
helpers are also consolidated, and modified to resemble the BUG module
helpers.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Originally, dwarf_unwind_stack() was a recursive function and it seems
that some of the old comments were never updated.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
If we broke out of the while (1) loop because the return address of
"frame" was zero, then "frame" needs to be free'd before we return.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Pass a module's .eh_frame section to the DWARF unwinder at module load
time so that the section's FDEs and CIEs can be registered with the
DWARF unwinder. This allows us to unwind the stack through module code
when generating backtraces.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
fix the following 'make includecheck' warning:
arch/sh/kernel/dwarf.c: asm/dwarf.h is included more than once.
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
The CIE and FDE structs are big enough and accessed regularly enough in
certain configurations to make cacheline alignment useful.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Allow a DWARF register to have an undefined value. When applied to the
DWARF return address register this lets lets us label a function as
having no direct caller, e.g. kernel_thread_helper().
Signed-off-by: Matt Fleming <matt@console-pimps.org>
The 'end' member of struct dwarf_fde denotes one byte past the end of
the CFA instruction stream for an FDE. The value of 'end' was being
calcualted incorrectly, it was being set too high. This resulted in
dwarf_cfa_execute_insns() interpreting data past the end of valid
instructions, thus causing all sorts of weird crashes.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
We can't assume that if we execute the unwinder code and the unwinder
was already running that it has faulted. Clearly two kernel threads can
invoke the unwinder at the same time and may be running simultaneously.
The previous approach used BUG() and BUG_ON() in the unwinder code to
detect whether the unwinder was incapable of unwinding the stack, and
that the next available unwinder should be used instead. A better
approach is to explicitly invoke a trap handler to switch unwinders when
the current unwinder cannot continue.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
