linux-kernel - [PATCH] vsprintf: uninline simple

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Message-ID: <82a2af6e-9b6c-4a09-89d7-ca90cc1cdad1@p183>
Date:   Fri, 27 Oct 2023 17:13:58 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] vsprintf: uninline simple_strntoull(), reorder arguments

* uninline simple_strntoull(),
  gcc overinlines and this function is not performance critical

* reorder arguments, so that appending INT_MAX as 4th argument
  generates very efficient tail call

Space savings:

	add/remove: 1/0 grow/shrink: 0/3 up/down: 27/-179 (-152)
	Function                            old     new   delta
	simple_strntoll                       -      27     +27
	simple_strtoull                      15      10      -5
	simple_strtoll                       41       7     -34
	vsscanf                            1930    1790    -140

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 lib/vsprintf.c |   25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -60,7 +60,8 @@
 bool no_hash_pointers __ro_after_init;
 EXPORT_SYMBOL_GPL(no_hash_pointers);
 
-static noinline unsigned long long simple_strntoull(const char *startp, size_t max_chars, char **endp, unsigned int base)
+noinline
+static unsigned long long simple_strntoull(const char *startp, char **endp, unsigned int base, size_t max_chars)
 {
 	const char *cp;
 	unsigned long long result = 0ULL;
@@ -95,7 +96,7 @@ static noinline unsigned long long simple_strntoull(const char *startp, size_t m
 noinline
 unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
 {
-	return simple_strntoull(cp, INT_MAX, endp, base);
+	return simple_strntoull(cp, endp, base, INT_MAX);
 }
 EXPORT_SYMBOL(simple_strtoull);
 
@@ -130,8 +131,8 @@ long simple_strtol(const char *cp, char **endp, unsigned int base)
 }
 EXPORT_SYMBOL(simple_strtol);
 
-static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
-				 unsigned int base)
+noinline
+static long long simple_strntoll(const char *cp, char **endp, unsigned int base, size_t max_chars)
 {
 	/*
 	 * simple_strntoull() safely handles receiving max_chars==0 in the
@@ -140,9 +141,9 @@ static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
 	 * and the content of *cp is irrelevant.
 	 */
 	if (*cp == '-' && max_chars > 0)
-		return -simple_strntoull(cp + 1, max_chars - 1, endp, base);
+		return -simple_strntoull(cp + 1, endp, base, max_chars - 1);
 
-	return simple_strntoull(cp, max_chars, endp, base);
+	return simple_strntoull(cp, endp, base, max_chars);
 }
 
 /**
@@ -155,7 +156,7 @@ static long long simple_strntoll(const char *cp, size_t max_chars, char **endp,
  */
 long long simple_strtoll(const char *cp, char **endp, unsigned int base)
 {
-	return simple_strntoll(cp, INT_MAX, endp, base);
+	return simple_strntoll(cp, endp, base, INT_MAX);
 }
 EXPORT_SYMBOL(simple_strtoll);
 
@@ -3648,13 +3649,11 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
 			break;
 
 		if (is_sign)
-			val.s = simple_strntoll(str,
-						field_width >= 0 ? field_width : INT_MAX,
-						&next, base);
+			val.s = simple_strntoll(str, &next, base,
+						field_width >= 0 ? field_width : INT_MAX);
 		else
-			val.u = simple_strntoull(str,
-						 field_width >= 0 ? field_width : INT_MAX,
-						 &next, base);
+			val.u = simple_strntoull(str, &next, base,
+						 field_width >= 0 ? field_width : INT_MAX);
 
 		switch (qualifier) {
 		case 'H':	/* that's 'hh' in format */