linux-kernel - [PATCH v2 20/22] nolibc/stdlib: Implement `getauxval(3)` function

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Message-Id: <20230110072434.3863-21-w@1wt.eu>
Date:   Tue, 10 Jan 2023 08:24:32 +0100
From:   Willy Tarreau <w@....eu>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Ammar Faizi <ammarfaizi2@...weeb.org>, Willy Tarreau <w@....eu>
Subject: [PATCH v2 20/22] nolibc/stdlib: Implement `getauxval(3)` function

From: Ammar Faizi <ammarfaizi2@...weeb.org>

Previous commits save the address of the auxiliary vector into a global
variable @_auxv. This commit creates a new function 'getauxval()' as a
helper function to get the auxv value based on the given key.

The behavior of this function is identic with the function documented
in 'man 3 getauxval'. This function is also needed to implement
'getpagesize()' function that we will wire up in the next patches.

Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 tools/include/nolibc/stdlib.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index a24000d1e822..894c955d027e 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -12,6 +12,7 @@
 #include "types.h"
 #include "sys.h"
 #include "string.h"
+#include <linux/auxvec.h>
 
 struct nolibc_heap {
 	size_t	len;
@@ -108,6 +109,32 @@ char *getenv(const char *name)
 	return _getenv(name, environ);
 }
 
+static __attribute__((unused))
+unsigned long getauxval(unsigned long type)
+{
+	const unsigned long *auxv = _auxv;
+	unsigned long ret;
+
+	if (!auxv)
+		return 0;
+
+	while (1) {
+		if (!auxv[0] && !auxv[1]) {
+			ret = 0;
+			break;
+		}
+
+		if (auxv[0] == type) {
+			ret = auxv[1];
+			break;
+		}
+
+		auxv += 2;
+	}
+
+	return ret;
+}
+
 static __attribute__((unused))
 void *malloc(size_t len)
 {
-- 
2.17.5