off single-stepping). Only do this on arches (only x86 so far)
which classify single-step traps unambiguously.
This allows other parts of the kernel to be intentionally and
unintentionally sloppy about generating single-step traps. On
x86, at least the following places were unintentionally sloppy:
- all operations that context-switched [er]flags. Especially
spinlock_enter()/exit() and cpu_switch(). When single-stepped,
saving the flags leaves PSL_T set in the saved flags, so
restoring gives a trap that is spurious if it occurs after
single-step mode has been left. Switching contexts away from
a low priority thread gives especially long-lived saved copies.
- the vm86 emulation allows user mode to set PSL_T. This was
correct until vm86 bios call mode was unintentionally given
access to kdb handling its single-step traps.
Now these places are intentionally sloppy, but unexpected
debugger traps still cause panics if no debugger that handles
the trap is attached when the trap is delivered.
current on first entry. This fixes a spurious "Stepping aborted"
message when the first entry is for a breakpoint.
Don't reset to the run mode to STEP_NONE when stopping, and remove
STEP_NONE. This mode was never really used, except transiently to
mis-decide whether to print the message on first entry.
This is not very easy to do, since ddb didn't know when traps are
for single-stepping. It more or less assumed that traps are either
breakpoints or single-step, but even for x86 this became inadequate
with the release of the i386 in ~1986, and FreeBSD passes it other
trap types for NMIs and panics.
On x86, teach ddb when a trap is for single stepping using the %dr6
register. Unknown traps are now treated almost the same as breakpoints
instead of as the same as single-steps. Previously, the classification
of breakpoints was almost correct and everything else was unknown so
had to be treated as a single-step. Now the classification of single-
steps is precise, the classification of breakpoints is almost correct
(as before) and everything else is unknown and treated like a
breakpoint.
This fixes:
- breakpoints not set by ddb, including the main one in kdb_enter(),
were treated as single-steps and not stopped on when stepping
(except for the usual, simple case of a step with residual count 1).
As special cases, kdb_enter() didn't stop for fatal traps or panics
- similarly for "hardware breakpoints".
Use a new MD macro IS_SSTEP_TRAP(type, code) to code to classify
single-steps. This is excessively complicated for bug-for-bug and
backwards compatibilty. Design errors apparently started in Mach
in ~1990 or perhaps in the FreeBSD interface in ~1993. Common trap
types like single steps should have a unique MI code (like the TRAP*
codes for user SIGTRAP) so that debuggers don't need macros like
IS_SSTEP_TRAP() to decode them. But 'type' is actually an ambiguous
MD trap number, and code was always 0 (now it is (int)%dr6 on x86).
So it was impossible to determine the trap type from the args.
Global variables had to be used.
There is already a classification macro db_pc_is_single_step(), but
this just gets in the way. It is only used to recover from bugs in
IS_BREAKPOINT_TRAP(). On some arches, IS_BREAKPOINT_TRAP() just
duplicates the ambiguity in 'type' and misclassifies single-steps as
breakpoints. It defaults to 'false', which is the opposite of what is
needed for bug-for-bug compatibility.
When this is cleaned up, MI classification bits should be passed in
'code'. This could be done now for positive-logic bits, since 'code'
was always 0, but some negative logic is needed for compatibility so
a simple MI classificition is not usable yet.
After reading %dr6, clear the single-step bit in it so that the type
of the next debugger trap can be decoded. This is a little
ddb-specific. ddb doesn't understand the need to clear this bit and
doing it before calling kdb is easiest. gdb would need to reverse
this to support hardware breakpoints, but it just doesn't support
them now since gdbstub doesn't support %dr*.
Fix a bug involving %dr6: when emulating a single-step trap for vm86,
set the bit for it in %dr6. Userland debuggers need this. ddb now
needs this for vm86 bios calls. The bit gets copied to 'code' then
cleared again.
Fix related style bugs:
- when clearing bits for hardware breakpoints in %dr6, spell the mask
as ~0xf on both amd64 and i386 to get the correct number of bits
using sign extension and not need a comment about using the wrong
mask on amd64 (amd64 traps for invalid results but clearing the
reserved top bits didn't trap since they are 0).
- rewrite my old wrong comments about using %dr6 for ddb watchpoints.
that the latter can easily determine what the trap type actually is
after callers are fixed to encode the type unambigously.
ddb currently barely understands breakpoints, and it treats all
non-breakpoints as single-step traps. This works OK for stopping
after every instruction when single-stepping, but is broken for
single-stepping with a count > 1 (especially with a large count).
ddb needs to stop on the first non-single-step trap while single-
stepping. Otherwise, ddb doesn't even stop the first time for
fatal traps and external breakpoints like the one in kdb_enter().
single stepping of multiple instructions (e.g., s/p,<count> and n/p).
db_print_loc_and_inst() already prints a newline on all arches although
it probably shouldn't.
Especially on SMP systems, single stepping tends to deadlock or panic
too quickly to be useful for anything except finding bugs in itself,
but with printing "itself" includes console drivers so it is useful
for generating stress tests for console drivers.
Some architectures (including ARMv6/v7) do not have separate single step
events and cannot see difference between breakpoint and single step.
Add db_pc_is_singlestep() to avoid skipping instruction we stepped on
to trigger debug event.
This commit does not change the existing functionality but adds possibility
to implement custom db_pc_is_singlestep().
Reviewed by: imp
Submitted by: Zbigniew Bodek <zbb@semihalf.com>
Obtained from: Semihalf
Sponsored by: Juniper Networks Inc.
Differential Revision: https://reviews.freebsd.org/D4036
The replacement started at r283088 was necessarily incomplete without
replacing boolean_t with bool. This also involved cleaning some type
mismatches and ansifying old C function declarations.
Pointed out by: bde
Discussed with: bde, ian, jhb
was satisified for the rest of the kernel on the i386 build except for
these two files. Rather than adding a submarine include to pcb.h, I've
added proc.h here.
I forgot to include these with the original commit. Sorry folks.
Most of the changes are a direct result of adding thread awareness.
Typically, DDB_REGS is gone. All registers are taken from the
trapframe and backtraces use the PCB based contexts. DDB_REGS was
defined to be a trapframe on all platforms anyway.
Thread awareness introduces the following new commands:
thread X switch to thread X (where X is the TID),
show threads list all threads.
The backtrace code has been made more flexible so that one can
create backtraces for any thread by giving the thread ID as an
argument to trace.
With this change, ia64 has support for breakpoints.
FreeBSD/alpha. The most significant item is to change the command
argument to ioctl functions from int to u_long. This change brings us
inline with various other BSD versions. Driver writers may like to
use (__FreeBSD_version == 300003) to detect this change.
The prototype FreeBSD/alpha machdep will follow in a couple of days
time.
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
to get the prototypes.
Changed some `int's to `boolean_t's. boolean_t's are ints so they are
hard to distinguish from ints.
Converted function headers to old-style. ddb is written in K&R1 C
except where we broke it.
``changes'' are actually not changes at all, but CVS sometimes has trouble
telling the difference.
This also includes support for second-directory compiles. This is not
quite complete yet, as `config' doesn't yet do the right thing. You can
still make it work trivially, however, by doing the following:
rm /sys/compile
mkdir /usr/obj/sys/compile
ln -s M-. /sys/compile
cd /sys/i386/conf
config MYKERNEL
cd ../../compile/MYKERNEL
ln -s /sys @
rm machine
ln -s @/i386/include machine
make depend
make
