This changes the definitions of a few items so that structures are the
same whether or not the option itself is enabled. This allows
people to enable and disable the option without recompilng the world.
As the author says:
|I ran into a problem pulling out the VM_STACK option. I was aware of this
|when I first did the work, but then forgot about it. The VM_STACK stuff
|has some code changes in the i386 branch. There need to be corresponding
|changes in the alpha branch before it can come out completely.
what is done:
|
|1) Pull the VM_STACK option out of the header files it appears in. This
|really shouldn't affect anything that executes with or without the rest
|of the VM_STACK patches. The vm_map_entry will then always have one
|extra element (avail_ssize). It just won't be used if the VM_STACK
|option is not turned on.
|
|I've also pulled the option out of vm_map.c. This shouldn't harm anything,
|since the routines that are enabled as a result are not called unless
|the VM_STACK option is enabled elsewhere.
|
|2) Add what appears to be appropriate code the the alpha branch, still
|protected behind the VM_STACK switch. I don't have an alpha machine,
|so we would need to get some testers with alpha machines to try it out.
|
|Once there is some testing, we can consider making the change permanent
|for both i386 and alpha.
|
[..]
|
|Once the alpha code is adequately tested, we can pull VM_STACK out
|everywhere.
|
Submitted by: "Richard Seaman, Jr." <dick@tar.com>
* Move the user stack from VM_MAXUSER_ADDRESS to a place below the 32bit
boundary (needed to support 32bit OSF programs). This should also save
one pagetable per process.
* Add cvtqlsv to the set of instructions handled by the floating point
software completion code.
* Disable all floating point exceptions by default.
* A minor change to execve to allow the OSF1 image activator to support
dynamic loading.
alpha, operations involving non-finite numbers or denormalised numbers
or operations which should generate such numbers will cause an arithmetic
exception. For programs which follow some strict code generation rules,
the kernel trap handler can then 'complete' the operation by emulating
the faulting instruction.
To use software completion, a program must be compiled with the arguments
'-mtrap-precision=i' and '-mfp-trap-mode=su' or '-mfp-trap-mode=sui'.
Programs compiled in this way can use non-finite and denormalised numbers
at the expense of slightly less efficient code generation of floating
point instructions. Programs not compiled with these options will receive
a SIGFPE signal when non-finite or denormalised numbers are used or
generated.
Reviewed by: John Polstra <jdp@polstra.com>
