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Re: [PATCH 4/9] bsd-user: Two helper routines oidfmt and sysctl_oldcvt


From: Richard Henderson
Subject: Re: [PATCH 4/9] bsd-user: Two helper routines oidfmt and sysctl_oldcvt
Date: Sat, 11 Feb 2023 12:17:09 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1

On 2/10/23 13:18, Warner Losh wrote:
+static int sysctl_oldcvt(void *holdp, size_t *holdlen, uint32_t kind)
+{
+    switch (kind & CTLTYPE) {
+    case CTLTYPE_INT:
+    case CTLTYPE_UINT:
+        *(uint32_t *)holdp = tswap32(*(uint32_t *)holdp);
+        break;
+
+#ifdef TARGET_ABI32
+    case CTLTYPE_LONG:
+    case CTLTYPE_ULONG:
+        /*
+         * If the sysctl has a type of long/ulong but seems to be bigger than
+         * these data types, its probably an array.  Double check that its
+         * evenly divisible by the size of long and convert holdp to a series 
of
+         * 32bit elements instead, adjusting holdlen to the new size.
+         */
+        if ((*holdlen > sizeof(abi_ulong)) &&
+            ((*holdlen % sizeof(abi_ulong)) == 0)) {
+            int array_size = *holdlen / sizeof(long);
+            int i;
+            if (holdp) {
+                for (i = 0; i < array_size; i++) {
+                    ((uint32_t *)holdp)[i] = tswap32(((long *)holdp)[i]);
+                }
+                *holdlen = array_size * sizeof(abi_ulong);
+            } else {
+                *holdlen = sizeof(abi_ulong);
+            }
+        } else {
+            *(uint32_t *)holdp = tswap32(*(long *)holdp);
+            *holdlen = sizeof(uint32_t);

This is totally confusing.  Why would it ever be an array?
Why is this section the only place we ever assign back into holdlen?

Can you point to anything similar in the freebsd source? The whole thing is pretty hard to track, starting from sys/kern/kern_sysctl.c.


r~



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