linux-kernel - [PATCH 2/2] lib/vsprintf: reduce space taken by no_hash

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Message-Id: <20210305194206.3165917-2-elver@google.com>
Date:   Fri,  5 Mar 2021 20:42:06 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com
Cc:     linux-kernel@...r.kernel.org, vbabka@...e.cz, timur@...nel.org,
        pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk, Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH 2/2] lib/vsprintf: reduce space taken by no_hash_pointers warning

Move the no_hash_pointers warning string into __initconst section, so
that it is discarded after init. Remove common start/end characters.
Also remove repeated lines from the array, since the compiler can't
remove duplicate strings for us since the array must appear in
__initconst as defined.

Note, a similar message appears in kernel/trace/trace.c, but compiling
the feature is guarded by CONFIG_TRACING. It is not immediately obvious
if a space-concious kernel would prefer CONFIG_TRACING=n. Therefore, it
makes sense to keep the message for no_hash_pointers as __initconst, and
not move the NOTICE-printing to a common function.

Link: https://lkml.kernel.org/r/CAMuHMdULKZCJevVJcp7TxzLdWLjsQPhE8hqxhnztNi9bjT_cEw@mail.gmail.com
Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Signed-off-by: Marco Elver <elver@...gle.com>
---
 lib/vsprintf.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4a14889ccb35..1095689c9c97 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2094,26 +2094,30 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
 bool no_hash_pointers __ro_after_init;
 EXPORT_SYMBOL_GPL(no_hash_pointers);
 
+static const char no_hash_pointers_warning[8][55] __initconst = {
+	"******************************************************",
+	"   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   ",
+	" This system shows unhashed kernel memory addresses   ",
+	" via the console, logs, and other interfaces. This    ",
+	" might reduce the security of your system.            ",
+	" If you see this message and you are not debugging    ",
+	" the kernel, report this immediately to your system   ",
+	" administrator!                                       ",
+};
+
 static int __init no_hash_pointers_enable(char *str)
 {
+	/* Indices into no_hash_pointers_warning; -1 is an empty line. */
+	const int lines[] = { 0, 1, -1, 2, 3, 4, -1, 5, 6, 7, -1, 1, 0 };
+	int i;
+
 	if (no_hash_pointers)
 		return 0;
 
 	no_hash_pointers = true;
 
-	pr_warn("**********************************************************\n");
-	pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
-	pr_warn("**                                                      **\n");
-	pr_warn("** This system shows unhashed kernel memory addresses   **\n");
-	pr_warn("** via the console, logs, and other interfaces. This    **\n");
-	pr_warn("** might reduce the security of your system.            **\n");
-	pr_warn("**                                                      **\n");
-	pr_warn("** If you see this message and you are not debugging    **\n");
-	pr_warn("** the kernel, report this immediately to your system   **\n");
-	pr_warn("** administrator!                                       **\n");
-	pr_warn("**                                                      **\n");
-	pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
-	pr_warn("**********************************************************\n");
+	for (i = 0; i < ARRAY_SIZE(lines); i++)
+		pr_warn("**%54s**\n", i == -1 ? "" : no_hash_pointers_warning[lines[i]]);
 
 	return 0;
 }
-- 
2.30.1.766.gb4fecdf3b7-goog