tree d63f7053cb6b5a69e05320ae00ece3f20f719710
parent 20ba6afe4c46be33b28dea80452432fb138d423e
author Tess Strickland <sstrickl@google.com> 1626162015 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1626162015 +0000

[vm] Merge text and data sections in ELF snapshots.

To do this, BitsContainer is changed to be a more rope-like
representation of section portions. In addition to containing
most of the same information stored per-section previously, each
portion also has a section-relative offset that is calculated when
it is added. Thus, merging two compatible BitsContainer sections
is just adding the portions from the second to the first, tweaking
the section-relative offset for each.

Other changes in this CL:

* Create PseudoSections subclasses for the elf header, program
  header table, and section header table, so we can treat them
  more uniformly with the other parts of the ELF snapshot.

* We now only allocate as much BSS space in the snapshot as is needed
  for any text sections in the snapshot, instead of always allocating
  a big enough BSS space for both VM and isolate, even for deferred
  snapshots where there is no VM isolate.

* We already separated segment and section alignment in previous CLs,
  so the fact that our own ELF loader needs load segments to be
  page-aligned no longer means that the sections within those segments
  also needs to be. Thus, we align individual instructions sections to
  kMaxObjectAlignment, like readonly data sections, since both hold a
  single Image object. This removes unnecessary intra-section padding.

TEST=Tests that check DWARF information and trybots that use ELF
     snapshots.

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-release-simarm-try,vm-kernel-precomp-linux-release-simarm64-try,vm-kernel-precomp-dwarf-linux-product-x64-try
Change-Id: If0315c8b7b0f31481b676a8901f49cd3a44b5561
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/206365
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>