[RFC v5 04/10] linux-user: Implement native-bypass option support

[Yeqi Fu]

This commit implements the -native-bypass support in linux-user. The
native_calls_enabled() function can be true only when the
'-native-bypass' option is given.

Signed-off-by: Yeqi Fu <fufuyqqqqqq@gmail.com>
---
 include/native/native.h |  9 +++++++++
 linux-user/main.c       | 38 ++++++++++++++++++++++++++++++++++++++
 linux-user/syscall.c    | 21 +++++++++++++++++++++
 3 files changed, 68 insertions(+)
 create mode 100644 include/native/native.h

diff --git a/include/native/native.h b/include/native/native.h
new file mode 100644
index 0000000000..7d1baadfcf
--- /dev/null
+++ b/include/native/native.h
@@ -0,0 +1,9 @@
+/*
+ * Check if the native bypass feature is enabled.
+ */
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_NATIVE_CALL)
+extern char *native_lib_path;
+#define native_bypass_enabled() (native_lib_path != NULL)
+#else
+#define native_bypass_enabled() false
+#endif
diff --git a/linux-user/main.c b/linux-user/main.c
index dba67ffa36..5cf02c071b 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -60,6 +60,11 @@
 #include "semihosting/semihost.h"
 #endif
 
+#if defined(CONFIG_NATIVE_CALL)
+#include "native/native.h"
+char *native_lib_path;
+#endif
+
 #ifndef AT_FLAGS_PRESERVE_ARGV0
 #define AT_FLAGS_PRESERVE_ARGV0_BIT 0
 #define AT_FLAGS_PRESERVE_ARGV0 (1 << AT_FLAGS_PRESERVE_ARGV0_BIT)
@@ -293,6 +298,17 @@ static void handle_arg_set_env(const char *arg)
     free(r);
 }
 
+#if defined(CONFIG_NATIVE_CALL)
+static void handle_arg_native_bypass(const char *arg)
+{
+    if (access(arg, F_OK) != 0) {
+        fprintf(stderr, "native library %s does not exist\n", arg);
+        exit(EXIT_FAILURE);
+    }
+    native_lib_path = g_strdup(arg);
+}
+#endif
+
 static void handle_arg_unset_env(const char *arg)
 {
     char *r, *p, *token;
@@ -522,6 +538,10 @@ static const struct qemu_argument arg_table[] = {
      "",           "Generate a /tmp/perf-${pid}.map file for perf"},
     {"jitdump",    "QEMU_JITDUMP",     false, handle_arg_jitdump,
      "",           "Generate a jit-${pid}.dump file for perf"},
+#if defined(CONFIG_NATIVE_CALL)
+    {"native-bypass", "QEMU_NATIVE_BYPASS", true, handle_arg_native_bypass,
+     "",           "native bypass for library calls"},
+#endif
     {NULL, NULL, false, NULL, NULL, NULL}
 };
 
@@ -834,6 +854,24 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
+#if defined(CONFIG_NATIVE_CALL)
+    /* Set the library for native bypass  */
+    if (native_lib_path) {
+        if (g_file_test(native_lib_path, G_FILE_TEST_IS_REGULAR)) {
+            GString *lib = g_string_new(native_lib_path);
+            lib = g_string_prepend(lib, "LD_PRELOAD=");
+            if (envlist_appendenv(envlist, g_string_free(lib, false), ":")) {
+                fprintf(stderr,
+                    "failed to append the native library to environment.\n");
+                exit(EXIT_FAILURE);
+            }
+        } else {
+            fprintf(stderr, "native library %s does not exist.\n",
+                    native_lib_path);
+            exit(EXIT_FAILURE);
+        }
+    }
+#endif
     target_environ = envlist_to_environ(envlist, NULL);
     envlist_free(envlist);
 
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 08162cc966..bd4c3045ff 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -143,6 +143,7 @@
 #include "fd-trans.h"
 #include "tcg/tcg.h"
 #include "cpu_loop-common.h"
+#include "native/native.h"
 
 #ifndef CLONE_IO
 #define CLONE_IO                0x80000000      /* Clone io context */
@@ -8626,6 +8627,7 @@ static int do_execveat(CPUArchState *cpu_env, int dirfd,
     abi_ulong addr;
     char **q;
     void *p;
+    unsigned int i;
 
     argc = 0;
 
@@ -8696,6 +8698,25 @@ static int do_execveat(CPUArchState *cpu_env, int dirfd,
         goto execve_efault;
     }
 
+    /*
+     * An error may occur when executing execv, stating that the
+     * shared library from LD_PRELOAD cannot be preloaded on a
+     * different arch. So, we find LD_PRELOAD and remove it from
+     * envp before executing the execv.
+     */
+    if (native_bypass_enabled()) {
+        i = 0;
+        while (envp[i] != NULL) {
+            if (strncmp(envp[i], "LD_PRELOAD=", 11) == 0) {
+                for (int j = i; envp[j] != NULL; j++) {
+                    envp[j] = envp[j + 1];
+                }
+            } else {
+                i++;
+            }
+        }
+    }
+
     if (is_proc_myself(p, "exe")) {
         ret = get_errno(safe_execveat(dirfd, exec_path, argp, envp, flags));
     } else {
-- 
2.34.1