Add support for readlinkat syscall

CMakeLists.txt

@@ -421,6 +421,7 @@ set(BASIC_TESTS
   read_nothing
   readdir
   readlink
+  readlinkat
   readv
   rlimit
   robust_futex

src/record_syscall.cc

@@ -2036,6 +2036,13 @@ static Switchable rec_prepare_syscall_arch(Task* t,
       return PREVENT_SWITCH;
     }
 
+    case Arch::readlinkat: {
+      syscall_state.reg_parameter(
+          3, ParamSize::from_syscall_result<typename Arch::ssize_t>(
+                 (size_t)t->regs().arg4()));
+      return PREVENT_SWITCH;
+    }
+
     case Arch::getgroups: {
       // We could record a little less data by restricting the recorded data
       // to the syscall result * sizeof(Arch::legacy_gid_t), but that would

src/syscalls.py

@@ -1420,7 +1420,7 @@ def __init__(self, **kwargs):
 renameat = UnsupportedSyscall(x86=302, x64=264)
 linkat = UnsupportedSyscall(x86=303, x64=265)
 symlinkat = UnsupportedSyscall(x86=304, x64=266)
-readlinkat = UnsupportedSyscall(x86=305, x64=267)
+readlinkat = IrregularEmulatedSyscall(x86=305, x64=267)
 fchmodat = UnsupportedSyscall(x86=306, x64=268)
 
 #  int faccessat(int dirfd, const char *pathname, int mode, int flags)

src/test/readlinkat.c

@@ -0,0 +1,42 @@
+/* -*- Mode: C; tab-width: 8; c-basic-offset: 2; indent-tabs-mode: nil; -*- */
+
+#include "rrutil.h"
+
+#define BUF_SIZE 10
+#define BUF2_SIZE 1000
+
+int main(int argc, char* argv[]) {
+  char path[] = "rr-test-file-XXXXXX";
+  char dpath[] = "rr-test-dir-XXXXXX";
+  const char *dir_path = mkdtemp(dpath);
+  int count;
+  char link[PATH_MAX];
+  char* buf = allocate_guard(BUF_SIZE, 'q');
+  char* buf2 = allocate_guard(BUF2_SIZE, 'r');
+
+  test_assert(0 <= dirfd);
+
+  chdir(dir_path);
+
+  for (count = 0;; ++count) {
+    sprintf(link, "rr-test-link-%d", count);
+    int ret = symlink(path, link);
+    if (ret == 0) {
+      break;
+    }
+    test_assert(errno == EEXIST);
+  }
+  int ret = readlinkat(AT_FDCWD, link, buf, BUF_SIZE);
+  test_assert(BUF_SIZE == ret);
+  test_assert(0 == memcmp(path, buf, BUF_SIZE));
+  verify_guard(BUF_SIZE, buf);
+
+  test_assert(strlen(path) == readlinkat(AT_FDCWD, link, buf2, BUF2_SIZE));
+  test_assert(0 == memcmp(path, buf2, strlen(path)));
+  verify_guard(BUF2_SIZE, buf2);
+
+  test_assert(0 == unlink(link));
+
+  atomic_puts("EXIT-SUCCESS");
+  return 0;
+}