clang compiler and #ident preprocessor directive - c++

Question

I've been working on modernizing our source management control and
compiler in my organization. We've been thus far using the Oracle
Developer Studio compilers on Solaris / Linux and the latest compiler
hasn't been supported on RHEL 8+. It also seems that it won't be
maintained in the future so I've started using clang. We've also in the
past been using RCS (ugh) and have been moving our C++ code into SVN
repositories in line with what we currently do for java projects.
Typically we use #ident tags to identify source information and comes in
handy, at least with RCS in looking for dirty headers etc. Checked out
files are less of an issue with SVN and compiling in our own
self-contained areas, but its still useful to have this information in
the object and eventual binary so we can determine differences between
releases easily.
It looks as if clang however, with the compiler options I've been using
doesn't use either #ident or the windows - #pragma comment(exestr,
"XXX"). At least nothing appears in the object as strings that I can see.
Is there any compiler options or pre-processor compiler options that I
can use with clang to retain this information?

Answer 1

That's a bit naughty, if clang accepts #ident but throws the string away.
This is actually a surprisingly intractable problem. Before the days of fiercely optimising compilers, it was sufficient to put, say:
static const char *id = "whatever";
at the top of each file, but no longer. If id isn't referenced anywhere, this now (a) generates a warning, and (b) has no effect. But you could try:
static const volatile char *id = "xxx";
^^^^^^^^
This compiles OK but I don't know whether the compiler puts the string in the object file; you'd have to check.
I don't suppose the prospect of editing every file in your codebase fills you with glee, but it looks like you have no choice if you want to get those strings in there.

Answer 2

In case anyone is interested. I ended up doing the following:
I added to the source a #pragma message
#ifdef __clang __
#pragma message ("VERSION File: $Id: $")
#else
#ident "VERSION File: $Id: $"
#endif
Note here, that SVN will populate the $Id keyword
#pragma message generates a warning in the compile output, so I created a bash script filter to redirect the output through. If it is a pragma message warning, it will put the version information into a THE_OBJECT_FILE.txt
#!/bin/sh
if [ -f $1.txt ]; then
\rm -rf $1.txt
touch $1.txt
fi
while read line
do
TEST=`echo $line | grep MAGENTA | grep VERSION`
if [ "$TEST" = "" ]; then
echo $TEST
else
TEST2=`echo $line | grep pragma-messages`
if [ "$TEST2" = "" ]; then
TEST3=`echo $line | awk -F'"' '{print $2}'`
echo $TEST3 >> $1.txt
fi
fi
done
After the object has been compiled and passed through the filter, use objcopy to embed the versioning into the comments section in the object.
#if [ -f "$#.txt" -a -f "$#" -a ! "$(FILTER_VERSION)" = "" ]; then
objcopy --add-section .version_information=$#.txt
--set-section-flags .version_information=noload,readonly $#; rm -f $#.txt;
fi