RFR(XS): 8214534: Setting of THIS_FILE in the build is broken (original) (raw)

Volker Simonis volker.simonis at gmail.com
Fri Nov 30 17:05:36 UTC 2018

Hi,

can I please have a review for the following trivial fix:

http://cr.openjdk.java.net/~simonis/webrevs/2018/8214534/ https://bugs.openjdk.java.net/browse/JDK-8214534

DISCLAIMER: "XS" refers to the size of the fix, not the size of the explanation :)

Currently the compilation of native files defines "THIS_FILE" to hold the name of the current compilation unit. However, setting "THIS_FILE" in NativeCompilation.gmk is broken and results in "THIS_FILE" always being the empty string. I first thought that this is just a simple quoting issue, but after I couldn't get it working, I found the following explanation in the GNU Make manual [1]:

"A common mistake is attempting to use $@ within the prerequisites list; this will not work. However, there is a special feature of GNU make, secondary expansion (see Secondary Expansion), which will allow automatic variable values to be used in prerequisite lists."

I'm not a Make expert, but I think this quote doesn't apply to "$@" only, but to all automatic variables. The proposed solution (i.e. "Secondary Expansion" [2]) seems overly complex for this problem. I think the solution in the patch is much simpler and works "just as well" :)

The other question is of course why do we need "THIS_FILE" at all? It is used for various native logs in the class library (not in HotSpot) which use the value of "THIS_FILE" to decorate their output with the current file name. On the other hand, we already have the standard, predefined "FILE" macro which could be used instead (and indeed, if "THIS_FILE" isn't defined, the various logging routines fall back to using "FILE").

The only explanation I could come up for having "THIS_FILE" until now is that "FILE" may contain the full path name of the compilation unit while we only want the simple file name (without path) in the log. However, in order to solve this "path" problem, we can use simpler solutions.

Some call sites (e.g. "src/jdk.jdwp.agent/share/native/libjdwp/log_messages.h") already use helper functions like "file_basename()" to cut off a potential path component from "THIS_FILE". Other call sites (e.g. "src/java.instrument/share/native/libinstrument/JPLISAssert.h" or "src/jdk.jdwp.agent/share/native/libjdwp/error_messages.h") currently simply use the value of "THIS_FILE" directly. But they could be easily fixed by either using "file_basename()" there as well or even simpler, wrapping "FILE" into another macro which calls "strrchr()" to do the same work.

So as a follow up to this change, I'd like to propose another change which completely removes "THIS_FILE" and changes all users of "THIS_FILE" to use "FILE" instead. This would also shorten our compile command lines (which doesn't happen too often :) What do you think?

Thank you and best regards, Volker

[1] https://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html [2] https://www.gnu.org/software/make/manual/html_node/Secondary-Expansion.html#Secondary-Expansion

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