linux-kernel - [PATCH nolibc 44/61] tools/nolibc/stdlib: add a simple getenv() implementation

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Date:   Mon, 18 Apr 2022 17:42:08 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     gwml@...r.gnuweeb.org, kernel-team@...com, w@....eu,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH nolibc 44/61] tools/nolibc/stdlib: add a simple getenv() implementation

From: Willy Tarreau <w@....eu>

This implementation relies on an extern definition of the environ
variable, that the caller must declare and initialize from envp.

Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/include/nolibc/stdlib.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 733105c574ee..aca8616335e3 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -60,6 +60,29 @@ int atoi(const char *s)
 	return atol(s);
 }
 
+/* Tries to find the environment variable named <name> in the environment array
+ * pointed to by global variable "environ" which must be declared as a char **,
+ * and must be terminated by a NULL (it is recommended to set this variable to
+ * the "envp" argument of main()). If the requested environment variable exists
+ * its value is returned otherwise NULL is returned.
+ */
+static __attribute__((unused))
+char *getenv(const char *name)
+{
+	extern char **environ;
+	int idx, i;
+
+	if (environ) {
+		for (idx = 0; environ[idx]; idx++) {
+			for (i = 0; name[i] && name[i] == environ[idx][i];)
+				i++;
+			if (!name[i] && environ[idx][i] == '=')
+				return &environ[idx][i+1];
+		}
+	}
+	return NULL;
+}
+
 /* Converts the unsigned long integer <in> to its hex representation into
  * buffer <buffer>, which must be long enough to store the number and the
  * trailing zero (17 bytes for "ffffffffffffffff" or 9 for "ffffffff"). The
-- 
2.31.1.189.g2e36527f23