From 46190922e0fb42d27bc7c8ed85d9fd44664f50ef Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sat, 28 Jun 2025 20:11:49 -0400
Subject: usr: libc: Store auxiliary vector tag/value pairs

This commit introduces the global libc '__libc_auxv' containing
auxiliary vector entries as per the System V Application Binary
Interface

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 lib/libc/src/main.c    | 33 ++++++++++++++++++++++++++++++---
 sys/include/sys/exec.h |  3 ++-
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/lib/libc/src/main.c b/lib/libc/src/main.c
index b178c07..02a648b 100644
--- a/lib/libc/src/main.c
+++ b/lib/libc/src/main.c
@@ -27,23 +27,50 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <sys/exec.h>
 #include <stdint.h>
 #include <stddef.h>
 
 extern int __libc_stdio_init(void);
 extern int __malloc_mem_init(void);
+uint64_t __libc_auxv[_AT_MAX];
 
 int main(int argc, char **argv);
 
+struct auxv_entry {
+    uint64_t tag;
+    uint64_t val;
+};
+
 int
 __libc_entry(uint64_t *ctx)
 {
+    const struct auxv_entry *auxvp;
     int status;
-    uint64_t argc;
+    uint64_t argc, envc, tag;
     char **argv;
+    char **envp;
+
+    argc = *ctx;
+    argv = (char **)(ctx + 1);
+    envp = (char **)(argv + argc + 1);
+
+    envc = 0;
+    while (envp[envc] != NULL) {
+        ++envc;
+    }
+
+    auxvp = (void *)(envp + envc + 1);
+    for (int i = 0; i < _AT_MAX; ++i) {
+        if (auxvp->tag == AT_NULL) {
+            break;
+        }
+        if (auxvp->tag < _AT_MAX) {
+            __libc_auxv[auxvp->tag] = auxvp->val;
+        }
 
-    argc = *(ctx++);
-    argv = (char **)((ctx++));
+        ++auxvp;
+    }
 
     if ((status = __libc_stdio_init()) != 0) {
         return status;
diff --git a/sys/include/sys/exec.h b/sys/include/sys/exec.h
index 7e720fc..aa2a729 100644
--- a/sys/include/sys/exec.h
+++ b/sys/include/sys/exec.h
@@ -32,7 +32,6 @@
 
 #include <sys/types.h>
 
-#if defined(_KERNEL)
 
 /* Danger: Do not change these !! */
 #define AT_NULL 0
@@ -45,7 +44,9 @@
 #define AT_RANDOM 7
 #define AT_EXECFN 8
 #define AT_PAGESIZE 9
+#define _AT_MAX 16
 
+#if defined(_KERNEL)
 #define MAX_PHDRS 32
 #define STACK_PUSH(PTR, VAL) *(--(PTR)) = VAL
 #define AUXVAL(PTR, TAG, VAL)   \
-- 
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