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Pistachio: make sure to generate global thread IDs

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The kernel distinguishes local from global IDs by looking at the lowest
6 bits of the thread ID (i.e., in 'L4_ThreadControl'). If those bits are
zero, the ID is interpreted as a local ID. Because those zero bits
overlap with the version bits of global IDs, this invariant could be
violated once the version of a global ID reaches 64. In this case,
'L4_ThreadControl' will return an error on the attempt to create a new
PD. To prevent this from happening, we always set the lowest bit to 1.
This commit is contained in:
Norman Feske 2012-02-25 14:35:37 +01:00
parent e085828725
commit 4e3be6b146
1 changed files with 10 additions and 2 deletions
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12
base-pistachio/src/core/include/platform_pd.h
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@ -36,7 +36,7 @@ namespace Genode {
enum {
PD_BITS = 9,
THREAD_BITS = 9,
VERSION_BITS = 14,
VERSION_BITS = 14 - 1, /* preserve 1 bit, see 'make_l4_id' */
PD_FIRST = 0,
PD_MAX = (1 << PD_BITS) - 1,
THREAD_MAX = (1 << THREAD_BITS) - 1,
@ -56,7 +56,15 @@ namespace Genode {
unsigned thread_no,
unsigned version)
{
return Pistachio::L4_GlobalId((pd_no << PD_BITS) | thread_no, version);
/*
* We have to make sure that the 6 lower version bits are
* never zero. Otherwise, the kernel won't recognize the
* thread ID as a global ID (i.e., 'L4_ThreadControl' would
* fail during the creation of a new PD). To maintain this
* invariant, we always set the lowest version bit to one.
*/
return Pistachio::L4_GlobalId((pd_no << PD_BITS) | thread_no,
(version << 1) | 1);
}