On 2014-02-21 00:43, Mike Duigou wrote:
Hello all;
This issue is a followon to JDK-8030350
(https://bugs.openjdk.java.net/browse/JDK-8030350) which enhanced the compiler
warnings used for compiling native code. The proposed changes principally
impact the Linux platform.
While 8030350 was focused on compiler warnings which did not impact code
generation, this changeset will, for some configurations, change the native
code generated and likely change performance. These proposed option changes
prevent specific types of relocation table, stack and heap memory corruption in
native code. Preventing these types of memory corruption may be useful for
finding certain kinds of bugs though and do provide some minimal additional
protections against malicious attacks. They aren't, by any means, a substitute
for following appropriate secure coding guidelines.
The rationale behind the implementation is as follows. For release builds
during the initial phase of JDK 9 I would like to enable only compile time
checks. This ends up being similar to the warnings in JDK-8030350. These
options have no runtime impact on footprint or performance and very minimal
additional compile time cost while providing value. **Release builds are not
expected to see any performance or footprint change as a result of this
changeset**
For fast debug builds we can enable linker protections (relro) and static
compile time bounds checks (FORTIFY_SOURCE=1). FORTIFY_SOURCE=1 might be moved
to the production builds as well because it has no runtime cost or executable
size cost.
For slow debug builds we can enable full linker protection (at a potential cost
in startup time), runtime bounds checks and stack protection (FORTIFY_SOURCE=2
-fprotect-stack-all). We will likely enable -fprotect-stack-strong when
available in GCC 4.9
The basis for enabling the additional protections in debug builds is that it
will help us find bugs in our native code and we aren't as concerned in debug
builds with footprint and performance. Since many developers already do their
personal builds in fastdebug or slowdebug mode for testing this will provide
good opportunity to shake out any problems with the options while not impacting
release builds. Should we find that any of the options provide significant
value for their cost we can move them to fastdebug or release. If any of the
options prove too costly they can be demoted or removed entirely.
https://bugs.openjdk.java.net/browse/JDK-8032045
http://cr.openjdk.java.net/~mduigou/JDK-8032045/2/webrev/
Additional to enabling the various compiler options I attempted to rationalize some of
the skew between the various hotspot/make/{platform}/makefiles/gcc.make files while
avoiding changing existing behaviour. I have also introduced the new -Og "optimize
for debugging" option and there are now an explicit C{XX}_O_FLAG_DEBUG definitions
to complement the C{XX}_O_FLAG_{DEBUG|NORM|HI|HIGHEST|NONE} optimization options.
Mike,
I have only looked at toolchain.m4.
First of all, I like the $C_O_FLAG_DEBUG logic.
Some questions/comments:
* Have you tested the -qnoopt option on xlc?
* This code and comment is not really aligned. Is the comment overly
broad, or is it a mistake in C_O_FLAG_HIGHEST?
# Disable optimization
C_O_FLAG_HIGHEST="$C_O_FLAG_NORM"
C_O_FLAG_HI="$C_O_FLAG_DEBUG"
* Maybe it's worth considering to extract the duplication of
"-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector-all --param
ssp-buffer-size=1" into a separate variable, something like
CFLAGS_EXTRA_CHECKS or whatever. The same argument is also valid for the
fastdebug extra switches, I think, even the amount of code duplication
is not as high. Hm. Actually. In fact, from what I can tell this change
will add these extra flags on all compilers, even though they are GCC
only (?). So breaking out these flags into a variable, that can be set
to empty if not using gcc, is probably not just a matter of style but a
matter of correctness.
* I'd also have a preference for moving the "compiler supports -Og"
check outside the actual flag setting. Maybe you can do the checking
first and set a variable indicating the availablility of this flag, e.g.
GCC_SUPPORTS_OG_FLAG, and then just check on that. The point here is
that it's hard as it is to see the pattern between different
optimization levels and compilers, but the more the code resembles a
simple structured assignment matrix, the easier it is to see it. With
checking code like this in the midst, it's easier to get lost.
/Magnus
