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Prevent different MSYS2 runtime versions from sharing cygheaps #192

Merged
merged 2 commits into from
Jul 8, 2024
Merged

Prevent different MSYS2 runtime versions from sharing cygheaps #192

merged 2 commits into from
Jul 8, 2024

Commits on Jan 30, 2024

  1. Avoid sharing cygheaps across Cygwin versions 

    It frequently leads to problems when trying, say, to call from MSYS2's
Bash into Cygwin's or Git for Windows', merely because sharing that data
is pretty finicky.

For example, using the MSYS2' Bash using the MSYS2 runtime version that
is current at time of writing, trying to call Cygwin's programs fails
in manners like this:

    $ /c/cygwin64/bin/uname -r
      0 [main] uname (9540) child_copy: cygheap read copy failed, 0x800000000..0x800010BE0, done 0, windows pid 9540, Win32 error 6
    680 [main] uname 880 C:\cygwin64\bin\uname.exe: *** fatal error - couldn't create signal pipe, Win32 error 5

with the rather misleading exit code 127 (a code which is reserved to
indicate that a command was not found).

Let's just treat the MSYS2 runtime and the Cygwin runtime as completely
incompatible with one another, by virtue of using a different
magic constant than merely `CHILD_INFO_MAGIC`.

By using the msys2-runtime commit to modify that magic constant, we can
even spawn programs using a different MSYS2 runtime (such as Git for
Windows') because the commit serves as the tell-tale whether two MSYS2
runtime versions are compatible with each other. To support building in
the MSYS2-packages repository (where we do not check out the
`msys2-runtime` but instead check out Cygwin and apply patches on top),
let's accept a hard-coded commit hash as `./configure` option.

One consequence is that spawned MSYS processes using a different MSYS2
runtime will not be visible as such to the parent process, i.e. they
cannot share any resources such as pseudo terminals. But that's okay,
they are simply treated as if they were regular Win32 programs.

Note: We have to use a very rare form of encoding the brackets in the
`expr` calls: quadrigraphs (for a thorough explanation, see
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.70/html_node/Quadrigraphs.html#Quadrigraphs).
This is necessary because it is apparently impossible to encode brackets
in `configure.ac` files otherwise.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jan 30, 2024
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  2. uname: report msys2-runtime commit hash, too 

    Having just Cygwin's version in the output of `uname` is not helpful, as
both MSYS2 as well as Git for Windows release intermediate versions of
the MSYS2 runtime much more often than Cygwin runtime versions are
released.

Signed-off-by: Johannes Schindelin <[email protected]>
    @dscho
    dscho committed Jan 30, 2024
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