linux-kernel - [PATCH 7/7] kdb: Simplify management of tmpbuffer in kdb

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Message-Id: <20240416-kgdb_read_refactor-v1-7-b18c2d01076d@linaro.org>
Date: Tue, 16 Apr 2024 11:43:24 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Jason Wessel <jason.wessel@...driver.com>, 
 Douglas Anderson <dianders@...omium.org>
Cc: kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: [PATCH 7/7] kdb: Simplify management of tmpbuffer in kdb_read()

The current approach to filling tmpbuffer with completion candidates is
confusing, with the buffer management being especially hard to reason
about. That's because it doesn't copy the completion canidate into
tmpbuffer, instead of copies a whole bunch of other nonsense and then
runs the completion stearch from the middle of tmpbuffer!

Change this to copy nothing but the completion candidate into tmpbuffer.

Pretty much everything else in this patch is renaming to reflect the
above change:

    s/p_tmp/tmpbuffer/
    s/buf_size/sizeof(tmpbuffer)/

Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
---
 kernel/debug/kdb/kdb_io.c | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 94a638a9d52fa..640208675c9a8 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -227,8 +227,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 	int count;
 	int i;
 	int diag, dtab_count;
-	int key, buf_size, ret;
-
+	int key, ret;
 
 	diag = kdbgetintenv("DTABCOUNT", &dtab_count);
 	if (diag)
@@ -310,21 +309,16 @@ static char *kdb_read(char *buffer, size_t bufsize)
 	case 9: /* Tab */
 		if (tab < 2)
 			++tab;
-		p_tmp = buffer;
-		while (*p_tmp == ' ')
-			p_tmp++;
-		if (p_tmp > cp)
-			break;
-		memcpy(tmpbuffer, p_tmp, cp-p_tmp);
-		*(tmpbuffer + (cp-p_tmp)) = '\0';
-		p_tmp = strrchr(tmpbuffer, ' ');
-		if (p_tmp)
-			++p_tmp;
-		else
-			p_tmp = tmpbuffer;
-		len = strlen(p_tmp);
-		buf_size = sizeof(tmpbuffer) - (p_tmp - tmpbuffer);
-		count = kallsyms_symbol_complete(p_tmp, buf_size);
+
+		tmp = *cp;
+		*cp = '\0';
+		p_tmp = strrchr(buffer, ' ');
+		p_tmp = (p_tmp ? p_tmp + 1 : buffer);
+		strscpy(tmpbuffer, p_tmp, sizeof(tmpbuffer));
+		*cp = tmp;
+
+		len = strlen(tmpbuffer);
+		count = kallsyms_symbol_complete(tmpbuffer, sizeof(tmpbuffer));
 		if (tab == 2 && count > 0) {
 			kdb_printf("\n%d symbols are found.", count);
 			if (count > dtab_count) {
@@ -336,14 +330,14 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			}
 			kdb_printf("\n");
 			for (i = 0; i < count; i++) {
-				ret = kallsyms_symbol_next(p_tmp, i, buf_size);
+				ret = kallsyms_symbol_next(tmpbuffer, i, sizeof(tmpbuffer));
 				if (WARN_ON(!ret))
 					break;
 				if (ret != -E2BIG)
-					kdb_printf("%s ", p_tmp);
+					kdb_printf("%s ", tmpbuffer);
 				else
-					kdb_printf("%s... ", p_tmp);
-				*(p_tmp + len) = '\0';
+					kdb_printf("%s... ", tmpbuffer);
+				tmpbuffer[len] = '\0';
 			}
 			if (i >= dtab_count)
 				kdb_printf("...");
@@ -354,14 +348,14 @@ static char *kdb_read(char *buffer, size_t bufsize)
 				kdb_position_cursor(kdb_prompt_str, buffer, cp);
 		} else if (tab != 2 && count > 0) {
 			/* How many new characters do we want from tmpbuffer? */
-			len_tmp = strlen(p_tmp) - len;
+			len_tmp = strlen(tmpbuffer) - len;
 			if (lastchar + len_tmp >= bufend)
 				len_tmp = bufend - lastchar;
 
 			if (len_tmp) {
 				/* + 1 ensures the '\0' is memmove'd */
 				memmove(cp+len_tmp, cp, (lastchar-cp) + 1);
-				memcpy(cp, p_tmp+len, len_tmp);
+				memcpy(cp, tmpbuffer+len, len_tmp);
 				kdb_printf("%s", cp);
 				cp += len_tmp;
 				lastchar += len_tmp;

-- 
2.43.0