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Cygwin: Treat Windows Store's "app execution aliases" as symbolic links

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When the Windows Store version of Python is installed, so-called "app
execution aliases" are put into the `PATH`. These are reparse points
under the hood, with an undocumented format.

We do know a bit about this format, though, as per the excellent analysis:
https://www.tiraniddo.dev/2019/09/overview-of-windows-execution-aliases.html

	The first 4 bytes is the reparse tag, in this case it's
	0x8000001B which is documented in the Windows SDK as
	IO_REPARSE_TAG_APPEXECLINK. Unfortunately there doesn't seem to
	be a corresponding structure, but with a bit of reverse
	engineering we can work out the format is as follows:

	Version: <4 byte integer>
	Package ID: <NUL Terminated Unicode String>
	Entry Point: <NUL Terminated Unicode String>
	Executable: <NUL Terminated Unicode String>
	Application Type: <NUL Terminated Unicode String>

Let's treat them as symbolic links. For example, in this developer's
setup, this will result in the following nice output:

	$ cd $LOCALAPPDATA/Microsoft/WindowsApps/

	$ ls -l python3.exe
	lrwxrwxrwx 1 me 4096 105 Aug 23  2020 python3.exe -> '/c/Program Files/WindowsApps/PythonSoftwareFoundation.Python.3.7_3.7.2544.0_x64__qbz5n2kfra8p0/python.exe'

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin 2021-03-22 16:51:41 +01:00 committed by Corinna Vinschen
parent 2533912fc7
commit 0631c6644e
1 changed files with 40 additions and 0 deletions
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40
winsup/cygwin/path.cc
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@ -2459,6 +2459,22 @@ symlink_info::check_sysfile (HANDLE h)
return res; return res;
} }
typedef struct _REPARSE_APPEXECLINK_BUFFER
{
DWORD ReparseTag;
WORD ReparseDataLength;
WORD Reserved;
struct {
DWORD Version; /* Take member name with a grain of salt. */
WCHAR Strings[1]; /* Four serialized, NUL-terminated WCHAR strings:
- Package ID
- Entry Point
- Executable Path
- Application Type
We're only interested in the Executable Path */
} AppExecLinkReparseBuffer;
} REPARSE_APPEXECLINK_BUFFER,*PREPARSE_APPEXECLINK_BUFFER;
static bool static bool
check_reparse_point_string (PUNICODE_STRING subst) check_reparse_point_string (PUNICODE_STRING subst)
{ {
@ -2558,6 +2574,30 @@ check_reparse_point_target (HANDLE h, bool remote, PREPARSE_DATA_BUFFER rp,
if (check_reparse_point_string (psymbuf)) if (check_reparse_point_string (psymbuf))
return PATH_SYMLINK | PATH_REP; return PATH_SYMLINK | PATH_REP;
} }
else if (!remote && rp->ReparseTag == IO_REPARSE_TAG_APPEXECLINK)
{
/* App execution aliases are commonly used by Windows Store apps. */
PREPARSE_APPEXECLINK_BUFFER rpl = (PREPARSE_APPEXECLINK_BUFFER) rp;
WCHAR *buf = rpl->AppExecLinkReparseBuffer.Strings;
DWORD size = rp->ReparseDataLength / sizeof (WCHAR), n;
/* It seems that app execution aliases have a payload of four
NUL-separated wide string: package id, entry point, executable
and application type. We're interested in the executable. */
for (int i = 0; i < 3 && size > 0; i++)
{
n = wcsnlen (buf, size - 1);
if (i == 2 && n > 0 && n < size)
{
RtlInitCountedUnicodeString (psymbuf, buf, n * sizeof (WCHAR));
return PATH_SYMLINK | PATH_REP;
}
if (i == 2)
break;
buf += n + 1;
size -= n + 1;
}
}
else if (rp->ReparseTag == IO_REPARSE_TAG_LX_SYMLINK) else if (rp->ReparseTag == IO_REPARSE_TAG_LX_SYMLINK)
{ {
/* WSL symlink. Problem: We have to convert the path to UTF-16 for /* WSL symlink. Problem: We have to convert the path to UTF-16 for