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* dcrt0.cc (get_cygwin_startup_info): Change zeros to DWORD array.

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Expect first DWORD in child_info struct being set to non-zero if
	wincap.needs_count_in_si_lpres2 is set.  Add comment to explain why.
	* fork.cc (frok::parent): Set ch.zero[0] to a sensible count value
	if wincap.needs_count_in_si_lpres2 is set.
	* spawn.cc (spawn_guts): Ditto.  Add filler bytes after ch on stack
	to accomodate needs_count_in_si_lpres2.
	* wincap.h: Define needs_count_in_si_lpres2 throughout.
	* wincap.cc: Ditto.
This commit is contained in:
Corinna Vinschen
2006-12-05 10:59:21 +00:00
parent 489bb390ce
commit c6674b53d3
6 changed files with 71 additions and 2 deletions
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28
winsup/cygwin/dcrt0.cc
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@@ -590,10 +590,36 @@ child_info *
get_cygwin_startup_info ()
{
STARTUPINFO si;
char zeros[sizeof (child_proc_info->zero)] = {0};
DWORD zeros[sizeof (child_proc_info->zero)
/ sizeof (child_proc_info->zero[0])] = {0};
GetStartupInfo (&si);
child_info *res = (child_info *) si.lpReserved2;
/* It appears that when running under WOW64 on Vista 64, the first DWORD
value in the datastructure lpReserved2 is pointing to (zero[0] in
Cygwin), has to reflect the size of that datastructure as used in the
Microsoft C runtime (a count value, counting the number of elements in
two subsequent arrays, BYTE[count and HANDLE[count]), even though the C
runtime isn't used. Otherwise, if zero[0] is 0 or too small, the
datastructure gets overwritten.
This seems to be a bug in Vista's WOW64, which apparently copies the
lpReserved2 datastructure not using the cbReserved2 size information,
but using the information given in the first DWORD within lpReserved2
instead. Funny enough, 32 bit Vista doesn't care if zero[0] is 0 or a
non-0 count value, while older versions of Windows might crash if
zero[0] is set to a non-zero value, as observed at least on XP 64.
exec/spawn as well as fork write an appropriate value into zero[0] now,
depending on the wincap.needs_count_in_si_lpres2 flag. The value is
sizeof (child_info_*) / 5 which results in a count which covers the
full datastructure, plus not more than 4 extra bytes. This is ok as
long as the child_info structure is cosily stored within a bigger
datastructure. */
if (wincap.needs_count_in_si_lpres2 ())
zeros[0] = si.cbReserved2 / 5;
if (si.cbReserved2 < EXEC_MAGIC_SIZE || !res
|| memcmp (res->zero, zeros, sizeof (res->zero)) != 0)
res = NULL;