Subject: bug#47596: File descriptor error when exiting emacs on android 11

From: Henrik Grimler <[email-masked]>
Date: Sun, 04 Apr 2021 21:20:35 +0200

Hi,

Android 10 introduced a new "file descriptor sanitizer" (fdsan, see [1]
for docs) which detects issues when opening and closing files across
multiple threads. On android 10 warnings were given, while on android
11 programs are killed instantly if issues are detected. 

Starting and then exiting emacs, or simply just running for example
`emacs --version`, gives an error. `gdb --args emacs --version` gives
this backtrace:

```
Starting program: /data/data/com.termux/files/usr/bin/emacs --version
GNU Emacs 27.2
Copyright (C) 2021 Free Software Foundation, Inc.
GNU Emacs comes with ABSOLUTELY NO WARRANTY.
You may redistribute copies of GNU Emacs
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING.
fdsan: attempted to close file descriptor 2, expected to be unowned,
actually owned by FILE* 0xb6c8800c

Program received signal SIGABRT, Aborted.
0xb63789e8 in fdsan_error(char const*, ...) ()
   from /apex/com.android.runtime/lib/bionic/libc.so
(gdb) bt full
#0  0xb63789e8 in fdsan_error(char const*, ...) ()
   from /apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#1  0xb63786fe in android_fdsan_close_with_tag ()
   from /apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#2  0xb63b83c0 in __sclose () from
/apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#3  0xb63b8f24 in __FILE_close(__sFILE*) ()
   from /apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#4  0x7f7e6a76 in close_stream (stream=0xb63cde44 <__sF+168>)
    at /home/builder/.termux-build/emacs/src/lib/close-stream.c:61
        some_pending = false
        prev_fail = false
        fclose_fail = 243
#5  0x7f68a872 in close_output_streams ()
    at /home/builder/.termux-build/emacs/src/src/sysdep.c:2840
        err = false
#6  0xb63c10d6 in __cxa_finalize ()
   from /apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#7  0xb63bc7b8 in exit () from
/apex/com.android.runtime/lib/bionic/libc.so
No symbol table info available.
#8  0x7f655d92 in main (argc=2, argv=0xbefff504)
    at /home/builder/.termux-build/emacs/src/src/emacs.c:1132
        version = 0xb5e68133 "27.2"
        copyright = 0xb5e68138 "Copyright (C) 2021 Free Software
Foundation, Inc."
        stack_bottom_variable = 0x7f655a61 <main>
        do_initial_setlocale = false
        no_loadup = false
        junk = 0x0
        dname_arg = 0x0
        ch_to_dir = 0x0
        original_pwd = 0x0
        dump_mode = 0x0
        skip_args = 1
        temacs = 0x0
        attempt_load_pdump = true
        sockfd = -1225460908
        module_assertions = 244
```

The emacs here was a debug build from the 27.2 tag, configured with:

 'configure --disable-dependency-tracking
 --prefix=/data/data/com.termux/files/usr
 --libdir=/data/data/com.termux/files/usr/lib
 --sbindir=/data/data/com.termux/files/usr/bin --disable-rpath
 --disable-rpath-hack --host=arm-linux-androideabi --disable-autodepend
 --with-gif=no --with-gnutls --with-jpeg=no --without-gconf
 --without-gsettings --without-lcms2 --without-x --with-png=no
 --with-tiff=no --with-xml2 --with-xpm=no --without-dbus
 --without-selinux --with-modules --with-pdumper=yes --with-
dumping=none
 --enable-checking=yes,glyphs --enable-check-lisp-object-type
 emacs_cv_sanitize_address=yes emacs_cv_prog_cc_no_pie=no
 ac_cv_lib_elf_elf_begin=no gl_cv_func_dup2_works=no
 ac_cv_func_setrlimit=no emacs_cv_func__setjmp=no
 emacs_cv_func_sigsetjmp=no --disable-nls --enable-shared
 --enable-static --libexecdir=/data/data/com.termux/files/usr/libexec
 'CFLAGS= -march=armv7-a -mfpu=neon -mfloat-abi=softfp -mthumb
 -fstack-protector-strong -g3 -O0 -Wall -gdwarf-4' 'CPPFLAGS=
 -D_FORTIFY_SOURCE=2 -D__USE_FORTIFY_LEVEL=2
 -I/data/data/com.termux/files/usr/include'
 'LDFLAGS=-L/data/data/com.termux/files/usr/lib
 -Wl,-rpath=/data/data/com.termux/files/usr/lib -march=armv7-a -fopenmp
 -static-openmp -Wl,--enable-new-dtags -Wl,--as-needed
 -Wl,-z,relro,-z,now''

Debugging these issues are very tedious in my experience so far
(probably easier for actual android apps). I will try to boil down the
relevant emacs code into a smaller program that still reproduces the
error.

Based on the backtrace it seem to be how stderr is opened (and closed)
that is problematic somehow.

Please let me know if you have any insights, or if I can provide
additional useful information.

Best regards,
Henrik Grimler

[1]
https://android.googlesource.com/platform/bionic/+/master/docs/fdsan.md