git: 28388d8abf8e - stable/12 - ddb: add ability to print user registers

[Mitchell Horne]

The branch stable/12 has been updated by mhorne:

URL: https://cgit.FreeBSD.org/src/commit/?id=28388d8abf8e2c7ac9247b138479832f96bcddc3

commit 28388d8abf8e2c7ac9247b138479832f96bcddc3
Author:     mhorne <mhorne at FreeBSD.org>
AuthorDate: 2020-12-18 20:06:46 +0000
Commit:     Mitchell Horne <mhorne at FreeBSD.org>
CommitDate: 2021-01-25 13:41:39 +0000

    ddb: add ability to print user registers
    
    Reviewed by:    jhb (earlier version), markj, bcr (manpages)
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit 088a7eef95b1f1919fe6eee722a57c4d4e1e0656)
---
 share/man/man4/ddb.4 | 10 +++-------
 sys/ddb/db_print.c   | 24 +++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/share/man/man4/ddb.4 b/share/man/man4/ddb.4
index 188b5c8fc5ec..28a54a49322d 100644
--- a/share/man/man4/ddb.4
+++ b/share/man/man4/ddb.4
@@ -934,14 +934,10 @@ at address
 Display the register set.
 If the
 .Cm u
-modifier is specified, it displays user registers instead of
-kernel registers or the currently saved one.
+modifier is specified, the register contents of the thread's previous
+trapframe are displayed instead.
+Usually, this corresponds to the saved state from userspace.
 .Pp
-.Sy Warning :
-The support of the
-.Cm u
-modifier depends on the machine.
-If not supported, incorrect information will be displayed.
 .\"
 .Pp
 .It Ic show Cm rman Ar addr
diff --git a/sys/ddb/db_print.c b/sys/ddb/db_print.c
index 3ff0b781532d..da929457984d 100644
--- a/sys/ddb/db_print.c
+++ b/sys/ddb/db_print.c
@@ -49,12 +49,32 @@ __FBSDID("$FreeBSD$");
 #include <ddb/db_sym.h>
 
 void
-db_show_regs(db_expr_t _1, bool _2, db_expr_t _3, char *_4)
+db_show_regs(db_expr_t _1, bool _2, db_expr_t _3, char *modif)
 {
+	struct trapframe *oldtf;
 	struct db_variable *regp;
 	db_expr_t value, offset;
 	const char *name;
 
+	/*
+	 * The 'u' modifier instructs us to print the previous trapframe, most
+	 * often containing state from userspace. This is done by temporarily
+	 * switching out kdb_frame.
+	 *
+	 * NB: curthread is used instead of kdb_thread, so that behaviour is
+	 * consistent with regular `show registers`, which always prints
+	 * curthread's trapframe.
+	 */
+	oldtf = kdb_frame;
+	if (modif[0] == 'u') {
+		if (curthread->td_frame == NULL ||
+		    curthread->td_frame == oldtf) {
+			db_printf("previous trapframe unavailable");
+			return;
+		}
+		kdb_frame = curthread->td_frame;
+	}
+
 	for (regp = db_regs; regp < db_eregs; regp++) {
 		if (!db_read_variable(regp, &value))
 			continue;
@@ -70,4 +90,6 @@ db_show_regs(db_expr_t _1, bool _2, db_expr_t _3, char *_4)
 		db_printf("\n");
 	}
 	db_print_loc_and_inst(PC_REGS());
+
+	kdb_frame = oldtf;
 }