linux-user: Make openat2() use -L for absolute paths

openat2() ignored the -L prefix and opened host files directly.
For example, openat2("/tmp/file") opened /tmp/file on the host, not
QEMU_LD_PREFIX/tmp/file like openat() does.

Fix this by using path() to rewrite absolute paths. Skip this
when RESOLVE_BENEATH or RESOLVE_IN_ROOT is set:
- RESOLVE_BENEATH rejects absolute paths anyway
- RESOLVE_IN_ROOT resolves relative to dirfd

Now openat() and openat2() work in the same way.

Link: https://gitlab.com/qemu-project/qemu/-/work_items/3341

Signed-off-by: Sun Haoyu <shyliuli@aosc.io>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20260317053827.25051-1-shyliuli@aosc.io
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/syscall.c

@@ -8856,7 +8856,16 @@ static int do_openat2(CPUArchState *cpu_env, abi_long dirfd,
     if (fd > -2) {
         ret = get_errno(fd);
     } else {
-        ret = get_errno(safe_openat2(dirfd, pathname, &how,
+        const char *host_pathname = pathname;
+        if (pathname[0] == '/' &&
+            !(how.resolve & (RESOLVE_IN_ROOT | RESOLVE_BENEATH))) {
+            /*
+             * RESOLVE_BENEATH rejects absolute paths; RESOLVE_IN_ROOT
+             * resolves them relative to dirfd.
+             */
+            host_pathname = path(pathname);
+        }
+        ret = get_errno(safe_openat2(dirfd, host_pathname, &how,
                                      sizeof(struct open_how_ver0)));
     }
 

linux-user/syscall_defs.h

@@ -2774,7 +2774,12 @@ struct target_open_how_ver0 {
 #ifndef RESOLVE_NO_SYMLINKS
 #define RESOLVE_NO_SYMLINKS     0x04
 #endif
-
+#ifndef RESOLVE_BENEATH
+#define RESOLVE_BENEATH         0x08
+#endif
+#ifndef RESOLVE_IN_ROOT
+#define RESOLVE_IN_ROOT         0x10
+#endif
 #if (defined(TARGET_I386) && defined(TARGET_ABI32)) || \
     (defined(TARGET_ARM) && defined(TARGET_ABI32)) || \
     defined(TARGET_M68K) || defined(TARGET_MICROBLAZE) || \