bsd-user: Implment madvise(2) to match the linux-user implementation.
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230925182709.4834-17-kariem.taha2.7@gmail.com>
diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
index 16c2259..b00ab3a 100644
--- a/bsd-user/bsd-mem.h
+++ b/bsd-user/bsd-mem.h
@@ -129,6 +129,59 @@
return get_errno(munlockall());
}
+/* madvise(2) */
+static inline abi_long do_bsd_madvise(abi_long arg1, abi_long arg2,
+ abi_long arg3)
+{
+ abi_ulong len;
+ int ret = 0;
+ abi_long start = arg1;
+ abi_long len_in = arg2;
+ abi_long advice = arg3;
+
+ if (start & ~TARGET_PAGE_MASK) {
+ return -TARGET_EINVAL;
+ }
+ if (len_in == 0) {
+ return 0;
+ }
+ len = TARGET_PAGE_ALIGN(len_in);
+ if (len == 0 || !guest_range_valid_untagged(start, len)) {
+ return -TARGET_EINVAL;
+ }
+
+ /*
+ * Most advice values are hints, so ignoring and returning success is ok.
+ *
+ * However, some advice values such as MADV_DONTNEED, are not hints and
+ * need to be emulated.
+ *
+ * A straight passthrough for those may not be safe because qemu sometimes
+ * turns private file-backed mappings into anonymous mappings.
+ * If all guest pages have PAGE_PASSTHROUGH set, mappings have the
+ * same semantics for the host as for the guest.
+ *
+ * MADV_DONTNEED is passed through, if possible.
+ * If passthrough isn't possible, we nevertheless (wrongly!) return
+ * success, which is broken but some userspace programs fail to work
+ * otherwise. Completely implementing such emulation is quite complicated
+ * though.
+ */
+ mmap_lock();
+ switch (advice) {
+ case MADV_DONTNEED:
+ if (page_check_range(start, len, PAGE_PASSTHROUGH)) {
+ ret = get_errno(madvise(g2h_untagged(start), len, advice));
+ if (ret == 0) {
+ page_reset_target_data(start, start + len - 1);
+ }
+ }
+ }
+ mmap_unlock();
+
+ return ret;
+}
+
/* minherit(2) */
static inline abi_long do_bsd_minherit(abi_long addr, abi_long len,
abi_long inherit)
