This patch revises the way coverage counter data writing takes place
to avoid problems where useful counter data (for user-written functions)
is skipped in favor of counter data from stdlib functions that are
executed "late in the game", during the counter writing process itself.
Reading counter values from a running "--coverpkg=all" program is an
inherently racy operation; while the the code that scans the coverage
counter segment is reading values, the program is still executing,
potentially updating those values, and updates can include execution
of previously un-executed functions. The existing counter data writing
code was using a two-pass model (initial sweep over the counter
segment to count live functions, second sweep to actually write data),
and wasn't properly accounting for the fact that the second pass could
see more functions than the first.
In the bug in question, the first pass discovered an initial set of
1240 functions, but by the time the second pass kicked in, several
additional new functions were also live. The second pass scanned the
counter segment again to write out exactly 1240 functions, but since
some of the counters for the newly executed functions were earlier in
the segment (due to linker layout quirks) than the user's selected
function, the sweep terminated before writing out counters for the
function of interest.
The fix rewrites the counter data file encoder to make a single sweep
over the counter segment instead of using a two-pass scheme.
Fixes#59563.
Change-Id: I5e908e226bb224adb90a2fb783013e52deb341da
Reviewed-on: https://go-review.googlesource.com/c/go/+/484535
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Than McIntosh <thanm@google.com>
Use the io.Seek* constants instead of their deprecated os.SEEK_*
counterparts.
Change-Id: Ie899f9cf286de7304a394d9a2a091a55937542ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/453576
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Delete some unused code, various cleanups to fix staticcheck warnings.
Change-Id: Ie475d57735a83351a4977f0dd4bc1387ce06a20e
Reviewed-on: https://go-review.googlesource.com/c/go/+/441935
Reviewed-by: David Chase <drchase@google.com>
Add utilities for reading and writing of counter data files as part of
the new code coverage implementation.
Trivia note: currently the contents of counter data files are emitted
in little-endian form, which for the counters is somewhat painful in
that we need to visit each counter value and properly encode it. It
might be better to instead emit counters in native endianity and then
teach the tools to decode properly in the case of an endianity
mismatch.
Updates #51430.
Change-Id: I124fdcb40fc339a48b64b35264bf24c3be50ddd4
Reviewed-on: https://go-review.googlesource.com/c/go/+/359403
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
