linux-user: Add code for PR_GET/SET_UNALIGN

This requires extra work for each target, but adds the
common syscall code, and the necessary flag in CPUState.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211227150127.2659293-4-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

cpu.c

@@ -174,13 +174,23 @@ void cpu_exec_unrealizefn(CPUState *cpu)
     cpu_list_remove(cpu);
 }
 
+/*
+ * This can't go in hw/core/cpu.c because that file is compiled only
+ * once for both user-mode and system builds.
+ */
 static Property cpu_common_props[] = {
-#ifndef CONFIG_USER_ONLY
+#ifdef CONFIG_USER_ONLY
+    /*
+     * Create a property for the user-only object, so users can
+     * adjust prctl(PR_SET_UNALIGN) from the command-line.
+     * Has no effect if the target does not support the feature.
+     */
+    DEFINE_PROP_BOOL("prctl-unalign-sigbus", CPUState,
+                     prctl_unalign_sigbus, false),
+#else
     /*
-     * Create a memory property for softmmu CPU object,
-     * so users can wire up its memory. (This can't go in hw/core/cpu.c
-     * because that file is compiled only once for both user-mode
-     * and system builds.) The default if no link is set up is to use
+     * Create a memory property for softmmu CPU object, so users can
+     * wire up its memory.  The default if no link is set up is to use
      * the system address space.
      */
     DEFINE_PROP_LINK("memory", CPUState, memory, TYPE_MEMORY_REGION,

include/hw/core/cpu.h

@@ -413,6 +413,9 @@ struct CPUState {
 
     bool ignore_memory_transaction_failures;
 
+    /* Used for user-only emulation of prctl(PR_SET_UNALIGN). */
+    bool prctl_unalign_sigbus;
+
     struct hax_vcpu_state *hax_vcpu;
 
     struct hvf_vcpu_state *hvf;

linux-user/generic/target_prctl_unalign.h

@@ -0,0 +1,27 @@
+/*
+ * Generic prctl unalign functions for linux-user
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#ifndef GENERIC_TARGET_PRCTL_UNALIGN_H
+#define GENERIC_TARGET_PRCTL_UNALIGN_H
+
+static abi_long do_prctl_get_unalign(CPUArchState *env, target_long arg2)
+{
+    CPUState *cs = env_cpu(env);
+    uint32_t res = PR_UNALIGN_NOPRINT;
+    if (cs->prctl_unalign_sigbus) {
+        res |= PR_UNALIGN_SIGBUS;
+    }
+    return put_user_u32(res, arg2);
+}
+#define do_prctl_get_unalign do_prctl_get_unalign
+
+static abi_long do_prctl_set_unalign(CPUArchState *env, target_long arg2)
+{
+    env_cpu(env)->prctl_unalign_sigbus = arg2 & PR_UNALIGN_SIGBUS;
+    return 0;
+}
+#define do_prctl_set_unalign do_prctl_set_unalign
+
+#endif /* GENERIC_TARGET_PRCTL_UNALIGN_H */

linux-user/syscall.c

@@ -6378,6 +6378,12 @@ static abi_long do_prctl_inval1(CPUArchState *env, abi_long arg2)
 #ifndef do_prctl_get_tagged_addr_ctrl
 #define do_prctl_get_tagged_addr_ctrl do_prctl_inval0
 #endif
+#ifndef do_prctl_get_unalign
+#define do_prctl_get_unalign do_prctl_inval1
+#endif
+#ifndef do_prctl_set_unalign
+#define do_prctl_set_unalign do_prctl_inval1
+#endif
 
 static abi_long do_prctl(CPUArchState *env, abi_long option, abi_long arg2,
                          abi_long arg3, abi_long arg4, abi_long arg5)
@@ -6441,6 +6447,11 @@ static abi_long do_prctl(CPUArchState *env, abi_long option, abi_long arg2,
         }
         return do_prctl_get_tagged_addr_ctrl(env);
 
+    case PR_GET_UNALIGN:
+        return do_prctl_get_unalign(env, arg2);
+    case PR_SET_UNALIGN:
+        return do_prctl_set_unalign(env, arg2);
+
     case PR_GET_DUMPABLE:
     case PR_SET_DUMPABLE:
     case PR_GET_KEEPCAPS:
@@ -6483,8 +6494,6 @@ static abi_long do_prctl(CPUArchState *env, abi_long option, abi_long arg2,
     case PR_SET_THP_DISABLE:
     case PR_GET_TSC:
     case PR_SET_TSC:
-    case PR_GET_UNALIGN:
-    case PR_SET_UNALIGN:
         /* Disable to prevent the target disabling stuff we need. */
         return -TARGET_EINVAL;