Re: [PATCH] Fix handling of null stap semaphores

[George Barrett <bob@bob131.so>]

On Mon, Dec 30, 2019 at 12:59:30PM -0500, Simon Marchi wrote:
> Yeah, I know writing a test case is not the most fun part, but it pays in
> the long run.  I can help if you are not familiar enough with
> tcl/expect/dejagnu.

I can stumble through enough to get something ready for review, but there is
a bit of a hiccup I wanted some advice on: the testing strategy you outlined
hinges on prepare_for_testing producing PIC executables, but AFAICS this is
neither done by default nor can I find a facility in the test suite utilities
to achieve this. Is adding -pie/-fPIC to additional_flags acceptable in this
instance?

On a related note, I was a bit surprised to discover that the test case
doesn't actually ever define USE_PROBES since the argument provided to
stap_test(_no_debuginfo) is `-DUSE_PROBES' instead of
`additional_flags=-DUSE_PROBES'. This seems like a trivial enough fix to be
rolled into a single commit, but I was thinking that the fix wouldn't be
particularly evident from the diff if the -pie flags were added in the same
patch. Would this be worth splitting into an independent patch?

> Hmm, it is not only glibc-specific (I believe?), but it also requires having
> glibc debug symbols installed.  I just tried in an Alpine docker image
> (which uses musl), and the address subtraction method works.  So between the
> two methods, I'd prefer the address subtraction, since it works on more
> libc's, and it works without debug info for the libc.

Indeed. I hadn't gotten far with testing an _r_debug approach before I
realised I was taking some things for granted.

> Simon

Thanks