Fork#40696: MSVCRT.DLL's _pgmptr variable is uninitialized by MinGW start-up code
Open Date: 2020-08-31 23:32
Last Update: 2020-09-01 20:31
URL for this Ticket:
https://osdn.net//projects/mingw/ticket/40696
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Last Changes/Comment on this Ticket:
2020-09-01 20:31 Updated by: keith
Comment:
The following (trivial) program illustrates the issue:
1. #include <stdio.h>
2. #include <stdlib.h>
3.
4. #ifdef _CRT_GLOB
5. int _CRT_glob = _CRT_GLOB;
6. #endif
7.
8. int main()
9. { printf( "_pgmptr = '%s'\n", _pgmptr );
10. return 0;
11. }
If I compile this, with default settings for _CRT_glob, link with current
mingwrt, and run it (under MSYS) on a Win7, or WinXP VM, I see:
$ mingw32-gcc t-pgmptr.c -o pgmptr.exe
$ ./pgmptr.exe
_pgmptr = '(null)'
OTOH, if I compile it with -D_CRT_GLOB=1, or with -D_CRT_GLOB=0, either of
which causes the mingwrt start-up code to call Microsoft's __getmainargs(), I
see (as expected):
$ mingw32-gcc -D_CRT_GLOB=1 t-pgmptr.c -o pgmptr.exe
$ ./pgmptr.exe
_pgmptr = 'e:\sandbox\pgmptr.exe'
Curiously, I didn't notice the anomalous default behaviour previously, (testing
on GNU/Linux, under Wine), because Wine's implementation of MSVCRT.DLL appears
to initialize _pgmptr without __getmainargs() having been called.
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Ticket Status:
Reporter: keith
Owner: keith
Type: Issues
Status: Open [Owner assigned]
Priority: 5 - Medium
MileStone: (None)
Component: WSL
Severity: 5 - Medium
Resolution: None
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Ticket details:
According to Microsoft's GetModulePathNameA() function documentation:
The global variable _pgmptr is automatically initialized to the full path of the executable file,
and can be used to retrieve the full path name of an executable file.
It appears that this global variable initialization occurs, only if the
run-time start-up code calls Microsoft's __getmainargs() function, but that
exhibits defective globbing of wild-card patterns, and MinGW has not used it,
as a default start-up hook, since the release of mingwrt-3.21, in December
2014. Consequently, references to _pgmptr, in code linked against mingwrt-3.21
(and later), are likely to dereference a NULL pointer.
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