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[RFC PATCH glibc 08/34] hurd: Disable O_TRUNC and FS_RETRY_MAGICAL in rt

From: Sergey Bugaev
Subject: [RFC PATCH glibc 08/34] hurd: Disable O_TRUNC and FS_RETRY_MAGICAL in rtld
Date: Sun, 19 Mar 2023 18:09:51 +0300

hurd/lookup-retry.c is compiled into rtld, the dynamic linker/loader. To
avoid pulling in file_set_size, file_utimens, tty/ctty stuff, more
string/memory code (memmove, strncpy, strcpy), and more strtoul/itoa
code, compile out support for O_TRUNC and FS_RETRY_MAGICAL when building
hurd/lookup-retry.c for rtld. None of that functionality is useful to
rtld during startup anyway. Keep support for FS_RETRY_MAGICAL("/"),
since that does not pull in much, and is required for following absolute

The large number of extra code being pulled into rtld was noticed by
reviewing librtld.map & elf/librtld.os.map in the build tree.

It is worth noting that once libc.so is loaded, the real __open, __stat,
etc. replace the minimal versions used initially by rtld -- this is
especially important in the Hurd port, where the minimal rtld versions
do not use the dtable and just pass real Mach port names as fds. Thus,
once libc.so is loaded, rtld will gain access to the full
__hurd_file_name_lookup_retry () version, complete with FS_RETRY_MAGICAL
support, which is important in case the program decides to
dlopen ("/proc/self/fd/...") or some such.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
 hurd/lookup-retry.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hurd/lookup-retry.c b/hurd/lookup-retry.c
index 8850c4fd..99c98104 100644
--- a/hurd/lookup-retry.c
+++ b/hurd/lookup-retry.c
@@ -177,7 +177,7 @@ __hurd_file_name_lookup_retry (error_t (*use_init_port)
              /* We got a successful translation.  Now apply any open-time
                 action flags we were passed.  */
+#if !IS_IN (rtld)
              if (!err && (flags & O_TRUNC))
                  /* Asked to truncate the file.  */
@@ -189,6 +189,7 @@ __hurd_file_name_lookup_retry (error_t (*use_init_port)
                      __file_utimens (*result, atime, mtime);
              if (err)
                __mach_port_deallocate (__mach_task_self (), *result);
@@ -214,6 +215,7 @@ __hurd_file_name_lookup_retry (error_t (*use_init_port)
              file_name = &retryname[1];
+#if !IS_IN (rtld)
            case 'f':
              if (retryname[1] == 'd' && retryname[2] == '/')
@@ -358,8 +360,9 @@ __hurd_file_name_lookup_retry (error_t (*use_init_port)
                goto bad_magic;
-           default:
+#endif /* !IS_IN (rtld) */
+           default:
              err = EGRATUITOUS;
              goto out;

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