Rework file shifting to avoid sections crossing multiple segments

[Bo98]

Fixes #403.

The previous logic was incorrect in some cases.

The way it worked before is we chose a point where to create a gap (startOffset), just after a .dynstr or the last non-interp PROGBITS. We then calculated how much space to add, move everything and create a PT_LOAD with that size.

The size of that PT_LOAD was incorrect however, as it only took into account the additional space we were adding - it did not take into account the space before startOffset, so it could be too small. The offsets of subsequent segments had similar logic. This created the potential for a section to overlap between segments.

To fix this, I've changed it so we don't add a new segment at all. Instead, we find the existing PT_LOAD segment that contains startOffset and increase the size of that by the calculated amount. Everything after startOffset is moved and has offsets adjusted as before, while everything before is now kept as is with only virtual memory offsets adjusted.

[Mic92]

This seems to cause some crashes now. You should be able to reproduce by running make check.

[Bo98]

I'm not actually:

============================================================================
Testsuite summary for patchelf 0.15.0
============================================================================
# TOTAL: 48
# PASS:  48
# SKIP:  0
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
============================================================================

Is there anything in particular I about the CI environment that I should be aware of in order to reproduce?

[Bo98]

Ah figured it out - it was Nix specific for some reason.

The original code made the new segment have RW flags. The new code didn't touch the flag so the original segment could have had just R.

So what I've done is instead produce two split segments like before rather than one large one, but still largely keeping the newer fixed logic that calculates the point to split at properly. This will reduce the diff a little and make it easier to compare.

[Mic92]

Thanks!

[haampie]

Thanks! Is it worth backporting this? Or cutting a new release?

[Mic92]

Yes, I think a new release is due.