Reviewed by enami@. Tested by Naruaki Etomi and me.
A 68k LUNA with this driver will be demonstrated at AsiaBSDCon NetBSD booth
by Etomi-san, with LUNA-88K2 running OpenBSD/luna88k by Kenji Aoyama.
This interface is modeled after FreeBSD API with the usage.
This replaced previous watchpoint API. The previous one was introduced
recently in NetBSD-current and remove its spurs without any
backward-compatibility.
Design choices for Debug Register accessors:
- exec() (TRAP_EXEC event) must remove debug registers from LWP
- debug registers are only per-LWP, not per-process globally
- debug registers must not be inherited after (v)forking a process
- debug registers must not be inherited after forking a thread
- a debugger is responsible to set global watchpoints/breakpoints with the
debug registers, to achieve this PTRACE_LWP_CREATE/PTRACE_LWP_EXIT event
monitoring function is designed to be used
- debug register traps must generate SIGTRAP with si_code TRAP_DBREG
- debugger is responsible to retrieve debug register state to distinguish
the exact debug register trap (DR6 is Status Register on x86)
- kernel must not remove debug register traps after triggering a trap event
a debugger is responsible to detach this trap with appropriate PT_SETDBREGS
call (DR7 is Control Register on x86)
- debug registers must not be exposed in mcontext
- userland must not be allowed to set a trap on the kernel
Implementation notes on i386 and amd64:
- the initial state of debug register is retrieved on boot and this value is
stored in a local copy (initdbregs), this value is used to initialize dbreg
context after PT_GETDBREGS
- struct dbregs is stored in pcb as a pointer and by default not initialized
- reserved registers (DR4-DR5, DR9-DR15) are ignored
Further ideas:
- restrict this interface with securelevel
Tested on real hardware i386 (Intel Pentium IV) and amd64 (Intel i7).
This commit enables 390 debug register ATF tests in kernel/arch/x86.
All tests are passing.
This commit does not cover netbsd32 compat code. Currently other interface
PT_GET_SIGINFO/PT_SET_SIGINFO is required in netbsd32 compat code in order to
validate reliably PT_GETDBREGS/PT_SETDBREGS.
This implementation does not cover FreeBSD specific defines in their
<x86/reg.h>: DBREG_DR7_LOCAL_ENABLE, DBREG_DR7_GLOBAL_ENABLE, DBREG_DR7_LEN_1
etc. These values tend to be reinvented by each tracer on its own. GNU
Debugger (GDB) works with NetBSD debug registers after adding this patch:
--- gdb/amd64bsd-nat.c.orig 2016-02-10 03:19:39.000000000 +0000
+++ gdb/amd64bsd-nat.c
@@ -167,6 +167,10 @@ amd64bsd_target (void)
#ifdef HAVE_PT_GETDBREGS
+#ifndef DBREG_DRX
+#define DBREG_DRX(d,x) ((d)->dr[(x)])
+#endif
+
static unsigned long
amd64bsd_dr_get (ptid_t ptid, int regnum)
{
Another reason to stop introducing unpopular defines covering machine
specific register macros is that these value varies across generations of
the same CPU family.
GDB demo:
(gdb) c
Continuing.
Watchpoint 2: traceme
Old value = 0
New value = 16
main (argc=1, argv=0x7f7fff79fe30) at test.c:8
8 printf("traceme=%d\n", traceme);
(Currently the GDB interface is not reliable due to NetBSD support bugs)
Sponsored by <The NetBSD Foundation>
Add a test program for the bug described in this PR.
This is the first pkill/pgrep/prenice test (more would be good!)
This test has been confirmed to work once the bug described in the PR
has been fixed, so the test is not marked "expected to fail" even
though initially that is what should happen.
Note: the test cana also fail if the system running the tests happens
to be running processes with names that match the patterns searched for
by the test, other than the test program itself. This is expected to be
unlikely.
