vkernel can not access debug registers
Nicolas Thery
nthery at gmail.com
Sun Oct 28 05:05:40 PDT 2007
I mistakenly pressed 'h' to get help in the vkernel ddb and got a bus error.
ddb interprets 'h' as 'hwatch' (set hardware watchpoint). This calls
db_md_set_watchpoint() which in turn calls fill_dbregs(). The latter
tries to access debug registers which triggers a GPF as the vkernel
runs in user mode.
Using 'show registers' also results in a GPF for the same reason.
This patch removes debug register code from the vkernel.
Index: dfly/src/sys/platform/vkernel/i386/db_trace.c
===================================================================
--- dfly.orig/src/sys/platform/vkernel/i386/db_trace.c 2007-10-27
09:50:50.108742000 +0200
+++ dfly/src/sys/platform/vkernel/i386/db_trace.c 2007-10-27
09:51:38.000000000 +0200
@@ -50,14 +50,7 @@
#include <ddb/db_sym.h>
#include <ddb/db_variables.h>
-db_varfcn_t db_dr0;
-db_varfcn_t db_dr1;
-db_varfcn_t db_dr2;
-db_varfcn_t db_dr3;
-db_varfcn_t db_dr4;
-db_varfcn_t db_dr5;
-db_varfcn_t db_dr6;
-db_varfcn_t db_dr7;
+static int db_dr(struct db_variable *vp, db_expr_t *valuep, int op);
/*
* Machine register set.
@@ -79,14 +72,14 @@
{ "edi", &ddb_regs.tf_edi, FCN_NULL },
{ "eip", &ddb_regs.tf_eip, FCN_NULL },
{ "efl", &ddb_regs.tf_eflags, FCN_NULL },
- { "dr0", NULL, db_dr0 },
- { "dr1", NULL, db_dr1 },
- { "dr2", NULL, db_dr2 },
- { "dr3", NULL, db_dr3 },
- { "dr4", NULL, db_dr4 },
- { "dr5", NULL, db_dr5 },
- { "dr6", NULL, db_dr6 },
- { "dr7", NULL, db_dr7 },
+ { "dr0", NULL, db_dr },
+ { "dr1", NULL, db_dr },
+ { "dr2", NULL, db_dr },
+ { "dr3", NULL, db_dr },
+ { "dr4", NULL, db_dr },
+ { "dr5", NULL, db_dr },
+ { "dr6", NULL, db_dr },
+ { "dr7", NULL, db_dr },
};
struct db_variable *db_eregs = db_regs + sizeof(db_regs)/sizeof(db_regs[0]);
@@ -112,10 +105,6 @@
static void dl_symbol_values(int callpc, const char **name);
-static char *watchtype_str(int type);
-static int ki386_set_watch(int watchnum, unsigned int watchaddr,
- int size, int access, struct dbreg * d);
-static int ki386_clr_watch(int watchnum, struct dbreg * d);
int db_md_set_watchpoint(db_expr_t addr, db_expr_t size);
int db_md_clr_watchpoint(db_expr_t addr, db_expr_t size);
void db_md_list_watchpoints(void);
@@ -405,201 +394,30 @@
db_stack_trace_cmd(ebp, 1, -1, NULL);
}
-#define DB_DRX_FUNC(reg) \
-int \
-db_ ## reg (struct db_variable *vp, db_expr_t *valuep, int op) \
-{ \
- if (op == DB_VAR_GET) \
- *valuep = r ## reg (); \
- else \
- load_ ## reg (*valuep); \
- \
- return(0); \
-}
-
-DB_DRX_FUNC(dr0)
-DB_DRX_FUNC(dr1)
-DB_DRX_FUNC(dr2)
-DB_DRX_FUNC(dr3)
-DB_DRX_FUNC(dr4)
-DB_DRX_FUNC(dr5)
-DB_DRX_FUNC(dr6)
-DB_DRX_FUNC(dr7)
-
static int
-ki386_set_watch(int watchnum, unsigned int watchaddr, int size, int access,
- struct dbreg *d)
+db_dr(struct db_variable *vp, db_expr_t *valuep, int op)
{
- int i;
- unsigned int mask;
-
- if (watchnum == -1) {
- for (i = 0, mask = 0x3; i < 4; i++, mask <<= 2)
- if ((d->dr7 & mask) == 0)
- break;
- if (i < 4)
- watchnum = i;
- else
- return(-1);
- }
-
- switch (access) {
- case DBREG_DR7_EXEC:
- size = 1; /* size must be 1 for an execution breakpoint */
- /* fall through */
- case DBREG_DR7_WRONLY:
- case DBREG_DR7_RDWR:
- break;
- default:
- return(-1);
- }
-
- /*
- * we can watch a 1, 2, or 4 byte sized location
- */
- switch (size) {
- case 1:
- mask = 0x00;
- break;
- case 2:
- mask = 0x01 << 2;
- break;
- case 4:
- mask = 0x03 << 2;
- break;
- default:
- return(-1);
- }
-
- mask |= access;
-
- /* clear the bits we are about to affect */
- d->dr7 &= ~((0x3 << (watchnum * 2)) | (0x0f << (watchnum * 4 + 16)));
-
- /* set drN register to the address, N=watchnum */
- DBREG_DRX(d, watchnum) = watchaddr;
-
- /* enable the watchpoint */
- d->dr7 |= (0x2 << (watchnum * 2)) | (mask << (watchnum * 4 + 16));
-
- return(watchnum);
+ if (op == DB_VAR_GET)
+ *valuep = 0;
+ return(-1);
}
-
-int
-ki386_clr_watch(int watchnum, struct dbreg *d)
-{
- if (watchnum < 0 || watchnum >= 4)
- return(-1);
-
- d->dr7 &= ~((0x3 << (watchnum * 2)) | (0x0f << (watchnum * 4 + 16)));
- DBREG_DRX(d, watchnum) = 0;
-
- return(0);
-}
-
-
int
db_md_set_watchpoint(db_expr_t addr, db_expr_t size)
{
- int avail, wsize;
- int i;
- struct dbreg d;
-
- fill_dbregs(NULL, &d);
-
- avail = 0;
- for(i=0; i < 4; i++) {
- if ((d.dr7 & (3 << (i * 2))) == 0)
- avail++;
- }
-
- if (avail * 4 < size)
- return(-1);
-
- for (i=0; i < 4 && (size != 0); i++) {
- if ((d.dr7 & (3 << (i * 2))) == 0) {
- if (size > 4)
- wsize = 4;
- else
- wsize = size;
- if (wsize == 3)
- wsize++;
- ki386_set_watch(i, addr, wsize, DBREG_DR7_WRONLY, &d);
- addr += wsize;
- size -= wsize;
- }
- }
-
- set_dbregs(NULL, &d);
-
- return(0);
+ return(-1);
}
int
db_md_clr_watchpoint(db_expr_t addr, db_expr_t size)
{
- int i;
- struct dbreg d;
-
- fill_dbregs(NULL, &d);
-
- for(i=0; i<4; i++) {
- if (d.dr7 & (3 << (i * 2))) {
- if ((DBREG_DRX((&d), i) >= addr) &&
- (DBREG_DRX((&d), i) < addr + size))
- ki386_clr_watch(i, &d);
- }
- }
-
- set_dbregs(NULL, &d);
-
- return(0);
-}
-
-static char *
-watchtype_str(int type)
-{
- switch (type) {
- case DBREG_DR7_EXEC:
- return "execute";
- case DBREG_DR7_RDWR:
- return "read/write";
- case DBREG_DR7_WRONLY:
- return "write";
- default:
- return "invalid";
- }
+ return(-1);
}
void
db_md_list_watchpoints(void)
{
- int i;
- struct dbreg d;
-
- fill_dbregs(NULL, &d);
-
- db_printf("\nhardware watchpoints:\n");
- db_printf(" watch status type len address\n"
- " ----- -------- ---------- --- ----------\n");
- for (i=0; i < 4; i++) {
- if (d.dr7 & (0x03 << (i * 2))) {
- unsigned type, len;
- type = (d.dr7 >> (16 + (i * 4))) & 3;
- len = (d.dr7 >> (16 + (i * 4) + 2)) & 3;
- db_printf(" %-5d %-8s %10s %3d 0x%08x\n",
- i, "enabled", watchtype_str(type),
- len + 1, DBREG_DRX((&d), i));
- } else {
- db_printf(" %-5d disabled\n", i);
- }
- }
-
- db_printf("\ndebug register values:\n");
- for (i=0; i < 8; i++)
- db_printf(" dr%d 0x%08x\n", i, DBREG_DRX((&d),i));
- db_printf("\n");
+ /* no hardware watchpoints in vkernel */
}
/*
Index: dfly/src/sys/platform/vkernel/i386/cpu_regs.c
===================================================================
--- dfly.orig/src/sys/platform/vkernel/i386/cpu_regs.c 2007-10-27
09:50:50.109229000 +0200
+++ dfly/src/sys/platform/vkernel/i386/cpu_regs.c 2007-10-27
09:51:38.000000000 +0200
@@ -1056,115 +1056,13 @@
int
fill_dbregs(struct lwp *lp, struct dbreg *dbregs)
{
- if (lp == NULL) {
- dbregs->dr0 = rdr0();
- dbregs->dr1 = rdr1();
- dbregs->dr2 = rdr2();
- dbregs->dr3 = rdr3();
- dbregs->dr4 = rdr4();
- dbregs->dr5 = rdr5();
- dbregs->dr6 = rdr6();
- dbregs->dr7 = rdr7();
- } else {
- struct pcb *pcb;
-
- pcb = lp->lwp_thread->td_pcb;
- dbregs->dr0 = pcb->pcb_dr0;
- dbregs->dr1 = pcb->pcb_dr1;
- dbregs->dr2 = pcb->pcb_dr2;
- dbregs->dr3 = pcb->pcb_dr3;
- dbregs->dr4 = 0;
- dbregs->dr5 = 0;
- dbregs->dr6 = pcb->pcb_dr6;
- dbregs->dr7 = pcb->pcb_dr7;
- }
- return (0);
+ return (ENOSYS);
}
int
set_dbregs(struct lwp *lp, struct dbreg *dbregs)
{
- if (lp == NULL) {
- load_dr0(dbregs->dr0);
- load_dr1(dbregs->dr1);
- load_dr2(dbregs->dr2);
- load_dr3(dbregs->dr3);
- load_dr4(dbregs->dr4);
- load_dr5(dbregs->dr5);
- load_dr6(dbregs->dr6);
- load_dr7(dbregs->dr7);
- } else {
- struct pcb *pcb;
- struct ucred *ucred;
- int i;
- uint32_t mask1, mask2;
-
- /*
- * Don't let an illegal value for dr7 get set. Specifically,
- * check for undefined settings. Setting these bit patterns
- * result in undefined behaviour and can lead to an unexpected
- * TRCTRAP.
- */
- for (i = 0, mask1 = 0x3<<16, mask2 = 0x2<<16; i < 8;
- i++, mask1 <<= 2, mask2 <<= 2)
- if ((dbregs->dr7 & mask1) == mask2)
- return (EINVAL);
-
- pcb = lp->lwp_thread->td_pcb;
- ucred = lp->lwp_proc->p_ucred;
-
- /*
- * Don't let a process set a breakpoint that is not within the
- * process's address space. If a process could do this, it
- * could halt the system by setting a breakpoint in the kernel
- * (if ddb was enabled). Thus, we need to check to make sure
- * that no breakpoints are being enabled for addresses outside
- * process's address space, unless, perhaps, we were called by
- * uid 0.
- *
- * XXX - what about when the watched area of the user's
- * address space is written into from within the kernel
- * ... wouldn't that still cause a breakpoint to be generated
- * from within kernel mode?
- */
-
- if (suser_cred(ucred, 0) != 0) {
- if (dbregs->dr7 & 0x3) {
- /* dr0 is enabled */
- if (dbregs->dr0 >= VM_MAX_USER_ADDRESS)
- return (EINVAL);
- }
-
- if (dbregs->dr7 & (0x3<<2)) {
- /* dr1 is enabled */
- if (dbregs->dr1 >= VM_MAX_USER_ADDRESS)
- return (EINVAL);
- }
-
- if (dbregs->dr7 & (0x3<<4)) {
- /* dr2 is enabled */
- if (dbregs->dr2 >= VM_MAX_USER_ADDRESS)
- return (EINVAL);
- }
-
- if (dbregs->dr7 & (0x3<<6)) {
- /* dr3 is enabled */
- if (dbregs->dr3 >= VM_MAX_USER_ADDRESS)
- return (EINVAL);
- }
- }
-
- pcb->pcb_dr0 = dbregs->dr0;
- pcb->pcb_dr1 = dbregs->dr1;
- pcb->pcb_dr2 = dbregs->dr2;
- pcb->pcb_dr3 = dbregs->dr3;
- pcb->pcb_dr6 = dbregs->dr6;
- pcb->pcb_dr7 = dbregs->dr7;
-
- pcb->pcb_flags |= PCB_DBREGS;
- }
-
- return (0);
+ return (ENOSYS);
}
#if 0
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