nptl: Check for compatible GDB in nptl/tst-pthread-gdb-attach

  Also do not clear the subprocess environment, in case running
GDB needs certain environment variables.

---
 nptl/tst-pthread-gdb-attach.c | 78 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 2 deletions(-)
  

On Thu, Apr 22, 2021 at 2:28 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> Also do not clear the subprocess environment, in case running
> GDB needs certain environment variables.
>
> ---
>  nptl/tst-pthread-gdb-attach.c | 78 +++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 76 insertions(+), 2 deletions(-)
>
> diff --git a/nptl/tst-pthread-gdb-attach.c b/nptl/tst-pthread-gdb-attach.c
> index 0603ad844d..901a120034 100644
> --- a/nptl/tst-pthread-gdb-attach.c
> +++ b/nptl/tst-pthread-gdb-attach.c
> @@ -20,8 +20,12 @@
>     whether libthread_db can be loaded, and that access to thread-local
>     variables works.  */
>
> +#include <elf.h>
>  #include <errno.h>
> +#include <fcntl.h>
> +#include <stdbool.h>
>  #include <stdlib.h>
> +#include <string.h>
>  #include <support/check.h>
>  #include <support/support.h>
>  #include <support/temp_file.h>
> @@ -35,6 +39,49 @@
>     the thread.  */
>  __thread volatile int altered_by_debugger;
>
> +/* Common prefix between 32-bit and 64-bit ELF.  */
> +struct elf_prefix
> +{
> +  unsigned char e_ident[EI_NIDENT];
> +  uint16_t e_type;
> +  uint16_t e_machine;
> +  uint32_t e_version;
> +};
> +_Static_assert (sizeof (struct elf_prefix) == EI_NIDENT + 8,
> +                "padding in struct elf_prefix");
> +
> +/* Reads the ELF header from PATH.  Returns true if the header can be
> +   read, false if the file is too short.  */
> +static bool
> +read_elf_header (const char *path, struct elf_prefix *elf)
> +{
> +  int fd = xopen (path, O_RDONLY, 0);
> +  bool result = read (fd, elf, sizeof (*elf)) == sizeof (*elf);
> +  xclose (fd);
> +  return result;
> +}
> +
> +/* Searches for "gdb" alongside the path variable.  See execvpe.  */
> +static char *
> +find_gdb (void)
> +{
> +  const char *path = getenv ("PATH");
> +  if (path == NULL)
> +    return NULL;
> +  while (true)
> +    {
> +      const char *colon = strchrnul (path, ':');
> +      char *candidate = xasprintf ("%.*s/gdb", (int) (colon - path), path);
> +      if (access (candidate, X_OK) == 0)
> +        return candidate;
> +      free (candidate);
> +      if (*colon == '\0')
> +        break;
> +      path = colon + 1;
> +    }
> +  return NULL;
> +}
> +
>  /* Writes the GDB script to run the test to PATH.  */
>  static void
>  write_gdbscript (const char *path, int tested_pid)
> @@ -105,6 +152,33 @@ in_subprocess (void)
>  static int
>  do_test (void)
>  {
> +  char *gdb_path = find_gdb ();
> +  if (gdb_path == NULL)
> +    FAIL_UNSUPPORTED ("gdb command not found in PATH: %s", getenv ("PATH"));
> +
> +  /* Check that libthread_db is compatible with the gdb architecture
> +     because gdb loads it via dlopen.  */
> +  {
> +    char *threaddb_path = xasprintf ("%s/nptl_db/libthread_db.so",
> +                                     support_objdir_root);
> +    struct elf_prefix elf_threaddb;
> +    TEST_VERIFY_EXIT (read_elf_header (threaddb_path, &elf_threaddb));
> +    struct elf_prefix elf_gdb;
> +    /* If the ELF header cannot be read or "gdb" is not an ELF file,
> +       assume this is a wrapper script that can run.  */
> +    if (read_elf_header (gdb_path, &elf_gdb)
> +        && memcmp (&elf_gdb, ELFMAG, SELFMAG) == 0)
> +      {
> +        if (elf_gdb.e_ident[EI_CLASS] != elf_threaddb.e_ident[EI_CLASS])
> +          FAIL_UNSUPPORTED ("GDB at %s has wrong class", gdb_path);
> +        if (elf_gdb.e_ident[EI_DATA] != elf_threaddb.e_ident[EI_DATA])
> +          FAIL_UNSUPPORTED ("GDB at %s has wrong data", gdb_path);
> +        if (elf_gdb.e_machine != elf_threaddb.e_machine)
> +          FAIL_UNSUPPORTED ("GDB at %s has wrong machine", gdb_path);
> +      }
> +    free (threaddb_path);
> +  }
> +
>    pid_t tested_pid = xfork ();
>    if (tested_pid == 0)
>      in_subprocess ();
> @@ -117,9 +191,8 @@ do_test (void)
>    pid_t gdb_pid = xfork ();
>    if (gdb_pid == 0)
>      {
> -      clearenv ();
>        xdup2 (STDOUT_FILENO, STDERR_FILENO);
> -      execlp ("gdb", "gdb", "-nx", "-batch", "-x", gdbscript, NULL);
> +      execl (gdb_path, "gdb", "-nx", "-batch", "-x", gdbscript, NULL);
>        if (errno == ENOENT)
>          _exit (EXIT_UNSUPPORTED);
>        else
> @@ -137,6 +210,7 @@ do_test (void)
>
>    free (tested_pid_string);
>    free (gdbscript);
> +  free (gdb_path);
>    return 0;
>  }
>
>

LGTM.

Thanks.