[PATCH v4 1/8] linux-user: Expose do_guest_openat() and do_guest_readlink()

[Ilya Leoshkevich <iii@linux.ibm.com>]

These functions will be required by the GDB stub in order to provide
the guest view of /proc to GDB.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/qemu.h    |  3 +++
 linux-user/syscall.c | 54 ++++++++++++++++++++++++++++----------------
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 92f9f5af41..a5830ec239 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -165,6 +165,9 @@ typedef struct TaskState {
 } TaskState;
 
 abi_long do_brk(abi_ulong new_brk);
+int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname,
+                    int flags, mode_t mode);
+ssize_t do_guest_readlink(const char *pathname, char *buf, size_t bufsiz);
 
 /* user access */
 
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index f2cb101d83..fa83737192 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8448,7 +8448,8 @@ static int open_hardware(CPUArchState *cpu_env, int fd)
 }
 #endif
 
-static int do_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int flags, mode_t mode)
+int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname,
+                    int flags, mode_t mode)
 {
     struct fake_open {
         const char *filename;
@@ -8520,6 +8521,36 @@ static int do_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int
     return safe_openat(dirfd, path(pathname), flags, mode);
 }
 
+ssize_t do_guest_readlink(const char *pathname, char *buf, size_t bufsiz)
+{
+    ssize_t ret;
+
+    if (!pathname || !buf) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    if (!bufsiz) {
+        /* Short circuit this for the magic exe check. */
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (is_proc_myself((const char *)pathname, "exe")) {
+        /*
+         * Don't worry about sign mismatch as earlier mapping
+         * logic would have thrown a bad address error.
+         */
+        ret = MIN(strlen(exec_path), bufsiz);
+        /* We cannot NUL terminate the string. */
+        memcpy(buf, exec_path, ret);
+    } else {
+        ret = readlink(path(pathname), buf, bufsiz);
+    }
+
+    return ret;
+}
+
 static int do_execveat(CPUArchState *cpu_env, int dirfd,
                        abi_long pathname, abi_long guest_argp,
                        abi_long guest_envp, int flags)
@@ -8994,7 +9025,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
     case TARGET_NR_open:
         if (!(p = lock_user_string(arg1)))
             return -TARGET_EFAULT;
-        ret = get_errno(do_openat(cpu_env, AT_FDCWD, p,
+        ret = get_errno(do_guest_openat(cpu_env, AT_FDCWD, p,
                                   target_to_host_bitmask(arg2, fcntl_flags_tbl),
                                   arg3));
         fd_trans_unregister(ret);
@@ -9004,7 +9035,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
     case TARGET_NR_openat:
         if (!(p = lock_user_string(arg2)))
             return -TARGET_EFAULT;
-        ret = get_errno(do_openat(cpu_env, arg1, p,
+        ret = get_errno(do_guest_openat(cpu_env, arg1, p,
                                   target_to_host_bitmask(arg3, fcntl_flags_tbl),
                                   arg4));
         fd_trans_unregister(ret);
@@ -10229,22 +10260,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
             void *p2;
             p = lock_user_string(arg1);
             p2 = lock_user(VERIFY_WRITE, arg2, arg3, 0);
-            if (!p || !p2) {
-                ret = -TARGET_EFAULT;
-            } else if (!arg3) {
-                /* Short circuit this for the magic exe check. */
-                ret = -TARGET_EINVAL;
-            } else if (is_proc_myself((const char *)p, "exe")) {
-                /*
-                 * Don't worry about sign mismatch as earlier mapping
-                 * logic would have thrown a bad address error.
-                 */
-                ret = MIN(strlen(exec_path), arg3);
-                /* We cannot NUL terminate the string. */
-                memcpy(p2, exec_path, ret);
-            } else {
-                ret = get_errno(readlink(path(p), p2, arg3));
-            }
+            ret = get_errno(do_guest_readlink(p, p2, arg3));
             unlock_user(p2, arg2, ret);
             unlock_user(p, arg1, 0);
         }
-- 
2.40.1