Disable the undefined behavior sanitizer by default

  There have been a few undefined behavior failures reported, and Pedro
suggested that the sanitizer be disabled by default.  This patch
implements this.

gdb/ChangeLog
2018-10-09  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.
	* sanitize.m4 (AM_GDB_UBSAN): Default to no.
	* NEWS: Update --enable-ubsan documentation.

gdb/doc/ChangeLog
2018-10-09  Tom Tromey  <tom@tromey.com>

	* gdb.texinfo (Configure Options): Update --enable-ubsan
	documentation.
---
 gdb/ChangeLog       |  6 ++++++
 gdb/NEWS            | 10 +++++-----
 gdb/configure       |  2 +-
 gdb/doc/ChangeLog   |  5 +++++
 gdb/doc/gdb.texinfo | 13 +++++++------
 gdb/sanitize.m4     |  2 +-
 6 files changed, 25 insertions(+), 13 deletions(-)
  

On 10/09/2018 07:02 PM, Tom Tromey wrote:
> There have been a few undefined behavior failures reported, and Pedro
> suggested that the sanitizer be disabled by default.  This patch
> implements this.

Thanks.  TBC, I think it'll be good to enable it by default.
But for now, we're already aware of a few issues that need
fixing, and the people fixing them can do --enable-ubsan
explicitly.

Please push.

> 
> gdb/ChangeLog
> 2018-10-09  Tom Tromey  <tom@tromey.com>
> 
> 	* configure: Rebuild.
> 	* sanitize.m4 (AM_GDB_UBSAN): Default to no.
> 	* NEWS: Update --enable-ubsan documentation.
> 
> gdb/doc/ChangeLog
> 2018-10-09  Tom Tromey  <tom@tromey.com>
> 
> 	* gdb.texinfo (Configure Options): Update --enable-ubsan
> 	documentation.
> ---
>  gdb/ChangeLog       |  6 ++++++
>  gdb/NEWS            | 10 +++++-----
>  gdb/configure       |  2 +-
>  gdb/doc/ChangeLog   |  5 +++++
>  gdb/doc/gdb.texinfo | 13 +++++++------
>  gdb/sanitize.m4     |  2 +-
>  6 files changed, 25 insertions(+), 13 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 8a0dd52fa7..126e61e282 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -122,11 +122,11 @@ FreeBSD/riscv			riscv*-*-freebsd*
>  
>  --enable-ubsan
>  
> -  Enable or disable the undefined behavior sanitizer.  Release
> -  versions of GDB disable this by default if it is available, but
> -  development versions enable it.  Enabling this can cause a
> -  performance penalty.  The undefined behavior sanitizer was first
> -  introduced in GCC 4.9.
> +  Enable or disable the undefined behavior sanitizer.  This is
> +  disabled by default, but passing --enable-ubsan=yes or
> +  --enable-ubsan=auto to configure will enable it.  Enabling this can
> +  cause a performance penalty.  The undefined behavior sanitizer was
> +  first introduced in GCC 4.9.
>  
>  *** Changes in GDB 8.2
>  
> diff --git a/gdb/configure b/gdb/configure
> index 304adc81fe..adb26e5d4d 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -15614,7 +15614,7 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
>  if test "${enable_ubsan+set}" = set; then :
>    enableval=$enable_ubsan;
>  else
> -  enable_ubsan=auto
> +  enable_ubsan=no
>  fi
>  
>  if test "x$enable_ubsan" = xauto; then
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index efd6dffb1e..b0dc3bf67c 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -35771,12 +35771,13 @@ to the compiler, which will fail the compilation if the compiler
>  outputs any warning messages.
>  
>  @item --enable-ubsan
> -Enable the GCC undefined behavior sanitizer.  By default this is
> -disabled in @value{GDBN} releases, but enabled, when available, when
> -building from git.  The undefined behavior sanitizer checks for
> -C@t{++} undefined behavior.  It has a performance cost, so if you are
> -looking at @value{GDBN}'s performance, you should disable it.  The
> -undefined behavior sanitizer was first introduced in GCC 4.9.
> +Enable the GCC undefined behavior sanitizer.  This is disabled by
> +default, but passing @code{--enable-ubsan=yes} or
> +@code{--enable-ubsan=auto} to @code{configure} will enable it.  The
> +undefined behavior sanitizer checks for C@t{++} undefined behavior.
> +It has a performance cost, so if you are looking at @value{GDBN}'s
> +performance, you should disable it.  The undefined behavior sanitizer
> +was first introduced in GCC 4.9.
>  @end table
>  
>  @node System-wide configuration
> diff --git a/gdb/sanitize.m4 b/gdb/sanitize.m4
> index 76df44da4f..979f6461c0 100644
> --- a/gdb/sanitize.m4
> +++ b/gdb/sanitize.m4
> @@ -20,7 +20,7 @@ AC_DEFUN([AM_GDB_UBSAN],[
>  AC_ARG_ENABLE(ubsan,
>    AS_HELP_STRING([--enable-ubsan],
>                   [enable undefined behavior sanitizer (auto/yes/no)]),
> -  [],enable_ubsan=auto)
> +  [],enable_ubsan=no)
>  if test "x$enable_ubsan" = xauto; then
>    if $development; then
>      enable_ubsan=yes
> 

Thanks,
Pedro Alves
  

> From: Tom Tromey <tom@tromey.com>
> Cc: Tom Tromey <tom@tromey.com>
> Date: Tue,  9 Oct 2018 12:02:31 -0600
> 
> There have been a few undefined behavior failures reported, and Pedro
> suggested that the sanitizer be disabled by default.  This patch
> implements this.
> 
> gdb/ChangeLog
> 2018-10-09  Tom Tromey  <tom@tromey.com>
> 
> 	* configure: Rebuild.
> 	* sanitize.m4 (AM_GDB_UBSAN): Default to no.
> 	* NEWS: Update --enable-ubsan documentation.
> 
> gdb/doc/ChangeLog
> 2018-10-09  Tom Tromey  <tom@tromey.com>
> 
> 	* gdb.texinfo (Configure Options): Update --enable-ubsan
> 	documentation.

OK for the documentation parts.

Thanks.