lower/raise); tex-suscript-height-ratio (how much smaller than
normal); tex-suscript-height-minimum (minimum height).
+** Screen refresh is slow when there are special characters for which no suitable font is available
+
+If the display is too slow in refreshing when you scroll to a new
+region, or when you edit the buffer, it might be due to the fact that
+some characters cannot be displayed in the default font, and Emacs is
+spending too much time in looking for a suitable font to display them.
+
+You can suspect this if you have several characters that are displayed
+as small rectangles containing a hexadecimal code inside.
+
+The solution is to install the appropriate fonts on your machine. For
+instance if you are editing a text with a lot of math symbols, then
+installing a font like 'Symbola' should solve this problem.
+
* Internationalization problems
** M-{ does not work on a Spanish PC keyboard.
** Window-manager and toolkit-related problems
+*** Emacs built with GTK+ toolkit produces corrupted display on HiDPI screen
+
+This can happen if you set GDK_SCALE=2 in the environment or in your
+'.xinitrc' file. (This setting is usually accompanied by
+GDK_DPI_SCALE=0.5.) Emacs can not support these settings correctly,
+as it doesn't use GTK+ exclusively. The result is that sometimes
+widgets like the scroll bar are displayed incorrectly, and frames
+could be displayed "cropped" to only part of the stuff that should be
+displayed.
+
+The workaround is to explicitly disable these settings when invoking
+Emacs, for example (from a Posix shell prompt):
+
+ $ GDK_SCALE=1 GDK_DPI_SCALE=1 emacs
+
*** Metacity: Resizing Emacs or ALT-Tab causes X to be unresponsive.
This happens sometimes when using Metacity. Resizing Emacs or ALT-Tab:bing
the 'xmodmap' utility to show all the keys which produce a Meta
modifier:
- xmodmap -pk | egrep -i "meta|alt"
+ xmodmap -pk | grep -Ei "meta|alt"
A more convenient way of finding out which keys produce a Meta modifier
is to use the 'xkbprint' utility, if it's available on your system:
(using the location of the 32-bit X libraries on your system).
+*** Building on FreeBSD 11 fails at link time due to unresolved symbol
+
+The symbol is sendmmsg@FBSD_1.4. This is due to a faulty libgio
+library on these systems. The solution is to reconfigure Emacs while
+disabling all the features that require libgio: rsvg, dbus, gconf, and
+imagemagick.
+
*** Building Emacs for Cygwin can fail with GCC 3
As of Emacs 22.1, there have been stability problems with Cygwin
** Dumping
-*** Segfault during 'make bootstrap' under the Linux kernel.
+*** Segfault during 'make'
-In Red Hat Linux kernels, "Exec-shield" functionality is enabled by
-default, which creates a different memory layout that can break the
-emacs dumper. Emacs tries to handle this at build time, but if this
-fails, the following instructions may be useful.
+If Emacs segfaults when 'make' executes one of these commands:
-Exec-shield is enabled on your system if
+ LC_ALL=C ./temacs -batch -l loadup bootstrap
+ LC_ALL=C ./temacs -batch -l loadup dump
- cat /proc/sys/kernel/exec-shield
+the problem may be due to inadequate workarounds for address space
+layout randomization (ASLR), an operating system feature that
+randomizes the virtual address space of a process. ASLR is commonly
+enabled in Linux and NetBSD kernels, and is intended to deter exploits
+of pointer-related bugs in applications. If ASLR is enabled, the
+command:
-prints a value other than 0. (Please read your system documentation
-for more details on Exec-shield and associated commands.)
+ cat /proc/sys/kernel/randomize_va_space # GNU/Linux
+ sysctl security.pax.aslr.global # NetBSD
-Additionally, Linux kernel versions since 2.6.12 randomize the virtual
-address space of a process by default. If this feature is enabled on
-your system, then
+outputs a nonzero value.
- cat /proc/sys/kernel/randomize_va_space
+These segfaults should not occur on most modern systems, because the
+Emacs build procedure uses the command 'setfattr' or 'paxctl' to mark
+the Emacs executable as requiring non-randomized address space, and
+Emacs uses the 'personality' system call to disable address space
+randomization when dumping. However, older kernels may not support
+'setfattr', 'paxctl', or 'personality', and newer Linux kernels have a
+secure computing mode (seccomp) that can be configured to disable the
+'personality' call.
-prints a value other than 0.
+It may be possible to work around the 'personality' problem in a newer
+Linux kernel by configuring seccomp to allow the 'personality' call.
+For example, if you are building Emacs under Docker, you can run the
+Docker container with a security profile that allows 'personality' by
+using Docker's --security-opt option with an appropriate profile; see
+<https://docs.docker.com/engine/security/seccomp/>.
-When these features are enabled, building Emacs may segfault during
-the execution of this command:
+To work around the ASLR problem in either an older or a newer kernel,
+you can temporarily disable the feature while building Emacs. On
+GNU/Linux you can do so using the following command (as root).
- ./temacs --batch --load loadup [dump|bootstrap]
+ echo 0 > /proc/sys/kernel/randomize_va_space
-To work around this problem, you can temporarily disable these
-features while building Emacs. You can do so using the following
-commands (as root). Remember to re-enable them when you are done,
-by echoing the original values back to the files.
+You can re-enable the feature when you are done, by echoing the
+original value back to the file. NetBSD uses a different command,
+e.g., 'sysctl -w security.pax.aslr.global=0'.
- echo 0 > /proc/sys/kernel/exec-shield
- echo 0 > /proc/sys/kernel/randomize_va_space
+Alternatively, you can try using the 'setarch' command when building
+temacs like this, where -R disables address space randomization:
+
+ setarch $(uname -m) -R make
-Or, on x86, you can try using the 'setarch' command when running
-temacs, like this:
+ASLR is not the only problem that can break Emacs dumping. Another
+issue is that in Red Hat Linux kernels, Exec-shield is enabled by
+default, and this creates a different memory layout. Emacs should
+handle this at build time, but if this fails the following
+instructions may be useful. Exec-shield is enabled on your system if
- setarch i386 -R ./temacs --batch --load loadup [dump|bootstrap]
+ cat /proc/sys/kernel/exec-shield
-or
+prints a nonzero value. You can temporarily disable it as follows:
- setarch i386 -R make
+ echo 0 > /proc/sys/kernel/exec-shield
-(The -R option disables address space randomization.)
+As with randomize_va_space, you can re-enable Exec-shield when you are
+done, by echoing the original value back to the file.
*** temacs prints "Pure Lisp storage exhausted".