Merge bde improvements for ddb on x86, mostly for single-stepping and

vm86 mode.

MFC r304085 (by bde):
Fix the variables $esp, $ds, $es, $fs, $gs and $ss in vm86 mode.  Fix
PC_REGS() so that printing of instructions works in some useful cases.

MFC r304962 (by bde):
Expand error messages: print symbol names, parentheses and shift tokens,
and negative shift counts.  Fix error messages.

MFC r305612 (by bde):
Fix single-stepping of instructions emulated by vm86.

MFC r305661 (by bde):
Give the full syntax of the 'count' arg for all commmands that support
it. Give the full syntax of the 'addr' arg for these commands and some
others.  Rename it from 'address' for the generic command. Fix
description of how 'count' is supposed to work for the 'break'
command.

Don't (mis)describe the syntax of the comma for the 'step' command.

Expand the description for the generic command.

Give the full syntax for the 'examine' command.  It was also missing
the possible values for the modifier.

MFC r305663 (by bde):
Fix stopping when the specified breakpoint count is reached.

MFC r305665 (by bde):
Pass the trap type and code down from db_trap() to db_stop_at_pc() so
that the latter can easily determine what the trap type actually is
after callers are fixed to encode the type unambigously.

MFC r305807 (by bde):
Use the MI macro TRAPF_USERMODE() instead of open-coded checks for
SEL_UPL and sometimes PSL_VM.  Fix logic errors in treating vm86
bioscall mode as kernel mode.  The main place checked all the
necessary flags, but put the necessary parentheses for the PSL_VM and
PCB_VM86CALL checks in the wrong place.

MFC r305811 (by bz):
Try to fix LINT builds after r305807.

MFC r305840 (by bde):
Abort single stepping in ddb if the trap is not for single-stepping.

MFC r305862 (by bde):
Ifdef the new dr6 variable for KDB.

MFC r305864 (by bde):
Statically initialize the run mode to the one that will become current
on first entry. Don't reset to the run mode to STEP_NONE when
stopping, and remove STEP_NONE.

MFC r305865 (by bde):
Fix decoding of tf_rsp on amd64, and move TF_HAS_STACKREGS() to the
i386-only section, and fix a comment about the amd64 kernel trapframe
not having stackregs.

MFC r305897 (by bde):
Silently ignore unexpected single-step traps.

MFC r306311 (by bde):
Determine the operand/address size of %cs in a new function
db_segsize().  Use db_segsize() to set the default operand/address
size for disassembling.

Fix db_print_loc_and_inst() to ask for the normal format and not the
alternate in normal operation. Use db_segsize() to avoid trying to
print a garbage stack trace if %cs is 16 bits.

5 files changed, 59 insertions, 27 deletions

diff --git a/sys/ddb/db_examine.c b/sys/ddb/db_examine.c
index de2bbe4..a1e5a28 100644
--- a/sys/ddb/db_examine.c
+++ b/sys/ddb/db_examine.c
@@ -241,7 +241,7 @@ db_print_loc_and_inst(db_addr_t loc)
 	db_printsym(loc, DB_STGY_PROC);
 	if (db_search_symbol(loc, DB_STGY_PROC, &off) != C_DB_SYM_NULL) {
 		db_printf(":\t");
-		(void)db_disasm(loc, true);
+		(void)db_disasm(loc, false);
 	}
 }
 
diff --git a/sys/ddb/db_expr.c b/sys/ddb/db_expr.c
index db17f36..c206a57 100644
--- a/sys/ddb/db_expr.c
+++ b/sys/ddb/db_expr.c
@@ -57,7 +57,8 @@ db_term(db_expr_t *valuep)
 	    if (!db_value_of_name(db_tok_string, valuep) &&
 		!db_value_of_name_pcpu(db_tok_string, valuep) &&
 		!db_value_of_name_vnet(db_tok_string, valuep)) {
-		db_error("Symbol not found\n");
+		db_printf("Symbol '%s' not found\n", db_tok_string);
+		db_error(NULL);
 		/*NOTREACHED*/
 	    }
 	    return (true);
@@ -89,12 +90,14 @@ db_term(db_expr_t *valuep)
 	}
 	if (t == tLPAREN) {
 	    if (!db_expression(valuep)) {
-		db_error("Syntax error\n");
+		db_printf("Expression syntax error after '%c'\n", '(');
+		db_error(NULL);
 		/*NOTREACHED*/
 	    }
 	    t = db_read_token();
 	    if (t != tRPAREN) {
-		db_error("Syntax error\n");
+		db_printf("Expression syntax error -- expected '%c'\n", ')');
+		db_error(NULL);
 		/*NOTREACHED*/
 	    }
 	    return (true);
@@ -164,7 +167,9 @@ db_mult_expr(db_expr_t *valuep)
 	while (t == tSTAR || t == tSLASH || t == tPCT || t == tHASH ||
 	    t == tBIT_AND ) {
 	    if (!db_term(&rhs)) {
-		db_printf("Expression syntax error after '%c'\n", '!');
+		db_printf("Expression syntax error after '%c'\n",
+		    t == tSTAR ? '*' : t == tSLASH ? '/' : t == tPCT ? '%' :
+		    t == tHASH ? '#' : '&');
 		db_error(NULL);
 		/*NOTREACHED*/
 	    }
@@ -177,7 +182,7 @@ db_mult_expr(db_expr_t *valuep)
 		    break;
 		default:
 		    if (rhs == 0) {
-			db_error("Divide by 0\n");
+			db_error("Division by 0\n");
 			/*NOTREACHED*/
 		    }
 		    if (t == tSLASH)
@@ -199,7 +204,6 @@ db_add_expr(db_expr_t *valuep)
 {
 	db_expr_t	lhs, rhs;
 	int		t;
-	char		c;
 
 	if (!db_mult_expr(&lhs))
 	    return (false);
@@ -207,8 +211,8 @@ db_add_expr(db_expr_t *valuep)
 	t = db_read_token();
 	while (t == tPLUS || t == tMINUS || t == tBIT_OR) {
 	    if (!db_mult_expr(&rhs)) {
-		c = db_tok_string[0];
-		db_printf("Expression syntax error after '%c'\n", c);
+		db_printf("Expression syntax error after '%c'\n",
+		    t == tPLUS ? '+' : t == tMINUS ? '-' : '|');
 		db_error(NULL);
 		/*NOTREACHED*/
 	    }
@@ -243,11 +247,14 @@ db_shift_expr(db_expr_t *valuep)
 	t = db_read_token();
 	while (t == tSHIFT_L || t == tSHIFT_R) {
 	    if (!db_add_expr(&rhs)) {
-		db_error("Syntax error\n");
+		db_printf("Expression syntax error after '%s'\n",
+		    t == tSHIFT_L ? "<<" : ">>");
+		db_error(NULL);
 		/*NOTREACHED*/
 	    }
 	    if (rhs < 0) {
-		db_error("Negative shift amount\n");
+		db_printf("Negative shift amount %jd\n", (intmax_t)rhs);
+		db_error(NULL);
 		/*NOTREACHED*/
 	    }
 	    if (t == tSHIFT_L)
@@ -269,7 +276,6 @@ db_logical_relation_expr(
 {
 	db_expr_t	lhs, rhs;
 	int		t;
-	char		op[3];
 
 	if (!db_shift_expr(&lhs))
 	    return (false);
@@ -277,11 +283,11 @@ db_logical_relation_expr(
 	t = db_read_token();
 	while (t == tLOG_EQ || t == tLOG_NOT_EQ || t == tGREATER ||
 	    t == tGREATER_EQ || t == tLESS || t == tLESS_EQ) {
-	    op[0] = db_tok_string[0];
-	    op[1] = db_tok_string[1];
-	    op[2] = 0;
 	    if (!db_shift_expr(&rhs)) {
-		db_printf("Expression syntax error after \"%s\"\n", op);
+		db_printf("Expression syntax error after '%s'\n",
+		    t == tLOG_EQ ? "==" : t == tLOG_NOT_EQ ? "!=" :
+		    t == tGREATER ? ">" : t == tGREATER_EQ ? ">=" :
+		    t == tLESS ? "<" : "<=");
 		db_error(NULL);
 		/*NOTREACHED*/
 	    }
diff --git a/sys/ddb/db_main.c b/sys/ddb/db_main.c
index 3345bb6..da6a513 100644
--- a/sys/ddb/db_main.c
+++ b/sys/ddb/db_main.c
@@ -226,10 +226,7 @@ db_trap(int type, int code)
 	if (cnunavailable())
 		return (0);
 
-	bkpt = IS_BREAKPOINT_TRAP(type, code);
-	watchpt = IS_WATCHPOINT_TRAP(type, code);
-
-	if (db_stop_at_pc(&bkpt)) {
+	if (db_stop_at_pc(type, code, &bkpt, &watchpt)) {
 		if (db_inst_count) {
 			db_printf("After %d instructions (%d loads, %d stores),\n",
 			    db_inst_count, db_load_count, db_store_count);
diff --git a/sys/ddb/db_run.c b/sys/ddb/db_run.c
index 5250651..4d8d3c7 100644
--- a/sys/ddb/db_run.c
+++ b/sys/ddb/db_run.c
@@ -48,15 +48,15 @@ __FBSDID("$FreeBSD$");
 #include <ddb/db_break.h>
 #include <ddb/db_access.h>
 
-static int	db_run_mode;
-#define	STEP_NONE	0
 #define	STEP_ONCE	1
 #define	STEP_RETURN	2
 #define	STEP_CALLT	3
 #define	STEP_CONTINUE	4
 #define	STEP_INVISIBLE	5
 #define	STEP_COUNT	6
+static int	db_run_mode = STEP_CONTINUE;
 
+static bool		db_sstep_multiple;
 static bool		db_sstep_print;
 static int		db_loop_count;
 static int		db_call_depth;
@@ -90,13 +90,14 @@ db_pc_is_singlestep(db_addr_t pc)
 #endif
 
 bool
-db_stop_at_pc(bool *is_breakpoint)
+db_stop_at_pc(int type, int code, bool *is_breakpoint, bool *is_watchpoint)
 {
 	db_addr_t	pc;
 	db_breakpoint_t bkpt;
 
+	*is_breakpoint = IS_BREAKPOINT_TRAP(type, code);
+	*is_watchpoint = IS_WATCHPOINT_TRAP(type, code);
 	pc = PC_REGS();
-
 	if (db_pc_is_singlestep(pc))
 		*is_breakpoint = false;
 
@@ -125,13 +126,39 @@ db_stop_at_pc(bool *is_breakpoint)
 		*is_breakpoint = true;
 		return (true);	/* stop here */
 	    }
+	    return (false);	/* continue the countdown */
 	} else if (*is_breakpoint) {
 #ifdef BKPT_SKIP
 		BKPT_SKIP;
 #endif
 	}
 
-	*is_breakpoint = false;
+	*is_breakpoint = false;	/* might be a breakpoint, but not ours */
+
+	/*
+	 * If not stepping, then silently ignore single-step traps
+	 * (except for clearing the single-step-flag above).
+	 *
+	 * If stepping, then abort if the trap type is unexpected.
+	 * Breakpoints owned by us are expected and were handled above.
+	 * Single-steps are expected and are handled below.  All others
+	 * are unexpected.
+	 *
+	 * Only do either of these if the MD layer claims to classify
+	 * single-step traps unambiguously (by defining IS_SSTEP_TRAP).
+	 * Otherwise, fall through to the bad historical behaviour
+	 * given by turning unexpected traps into expected traps: if not
+	 * stepping, then expect only breakpoints and stop, and if
+	 * stepping, then expect only single-steps and step.
+	 */
+#ifdef IS_SSTEP_TRAP
+	if (db_run_mode == STEP_CONTINUE && IS_SSTEP_TRAP(type, code))
+	    return (false);
+	if (db_run_mode != STEP_CONTINUE && !IS_SSTEP_TRAP(type, code)) {
+	    printf("Stepping aborted\n");
+	    return (true);
+	}
+#endif
 
 	if (db_run_mode == STEP_INVISIBLE) {
 	    db_run_mode = STEP_CONTINUE;
@@ -184,7 +211,6 @@ db_stop_at_pc(bool *is_breakpoint)
 		return (false);	/* continue */
 	    }
 	}
-	db_run_mode = STEP_NONE;
 	return (true);
 }
 
@@ -194,6 +220,7 @@ db_restart_at_pc(bool watchpt)
 	db_addr_t	pc = PC_REGS();
 
 	if ((db_run_mode == STEP_COUNT) ||
+	    ((db_run_mode == STEP_ONCE) && db_sstep_multiple) ||
 	    (db_run_mode == STEP_RETURN) ||
 	    (db_run_mode == STEP_CALLT)) {
 	    /*
@@ -321,6 +348,7 @@ db_single_step_cmd(db_expr_t addr, bool have_addr, db_expr_t count, char *modif)
 
 	db_run_mode = STEP_ONCE;
 	db_loop_count = count;
+	db_sstep_multiple = (count != 1);
 	db_sstep_print = print;
 	db_inst_count = 0;
 	db_load_count = 0;
diff --git a/sys/ddb/ddb.h b/sys/ddb/ddb.h
index a2adcdf..fcf772b 100644
--- a/sys/ddb/ddb.h
+++ b/sys/ddb/ddb.h
@@ -215,7 +215,8 @@ void		db_restart_at_pc(bool watchpt);
 int		db_set_variable(db_expr_t value);
 void		db_set_watchpoints(void);
 void		db_skip_to_eol(void);
-bool		db_stop_at_pc(bool *is_breakpoint);
+bool		db_stop_at_pc(int type, int code, bool *is_breakpoint,
+		    bool *is_watchpoint);
 #define		db_strcpy	strcpy
 void		db_trace_self(void);
 int		db_trace_thread(struct thread *, int);