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238669 |
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21-Jul-2012 |
kib |
The PT_I386_{GET,SET}XMMREGS and PT_{GET,SET}XSTATE operate on the
stopped threads. Implementation assumes that the thread's FPU context
is spilled into the PCB due to stop. This is mostly true, except when
FPU state for the thread is not initialized. Then the requests operate
on the garbage state which is currently left in the PCB, causing
confusion.
The situation is indeed observed after a signal delivery and before
#NM fault on execution of any FPU instruction in the signal handler,
since sendsig(9) drops FPU state for current thread, clearing
PCB_FPUINITDONE. When inspecting context state for the signal handler,
debugger sees the FPU state of the main program context instead of the
clear state supposed to be provided to handler.
Fix this by forcing clean FPU state in PCB user FPU save area by
performing getfpuregs(9) before accessing user FPU save area in
ptrace_machdep.c.
Note: this change will be merged to i386 kernel as well, where it is
much more important, since e.g. gdb on i386 uses PT_I386_GETXMMREGS to
inspect FPU context on CPUs that support SSE. Amd64 version of gdb
uses PT_GETFPREGS to inspect both 64 and 32 bit processes, which does
not exhibit the bug.
Reported by: bde
MFC after: 1 week
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| #
230426 |
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21-Jan-2012 |
kib |
Add support for the extended FPU states on amd64, both for native
64bit and 32bit ABIs. As a side-effect, it enables AVX on capable
CPUs.
In particular:
- Query the CPU support for XSAVE, list of the supported extensions
and the required size of FPU save area. The hw.use_xsave tunable is
provided for disabling XSAVE, and hw.xsave_mask may be used to
select the enabled extensions.
- Remove the FPU save area from PCB and dynamically allocate the
(run-time sized) user save area on the top of the kernel stack,
right above the PCB. Reorganize the thread0 PCB initialization to
postpone it after BSP is queried for save area size.
- The dumppcb, stoppcbs and susppcbs now do not carry the FPU state as
well. FPU state is only useful for suspend, where it is saved in
dynamically allocated suspfpusave area.
- Use XSAVE and XRSTOR to save/restore FPU state, if supported and
enabled.
- Define new mcontext_t flag _MC_HASFPXSTATE, indicating that
mcontext_t has a valid pointer to out-of-struct extended FPU
state. Signal handlers are supplied with stack-allocated fpu
state. The sigreturn(2) and setcontext(2) syscall honour the flag,
allowing the signal handlers to inspect and manipilate extended
state in the interrupted context.
- The getcontext(2) never returns extended state, since there is no
place in the fixed-sized mcontext_t to place variable-sized save
area. And, since mcontext_t is embedded into ucontext_t, makes it
impossible to fix in a reasonable way. Instead of extending
getcontext(2) syscall, provide a sysarch(2) facility to query
extended FPU state.
- Add ptrace(2) support for getting and setting extended state; while
there, implement missed PT_I386_{GET,SET}XMMREGS for 32bit binaries.
- Change fpu_kern KPI to not expose struct fpu_kern_ctx layout to
consumers, making it opaque. Internally, struct fpu_kern_ctx now
contains a space for the extended state. Convert in-kernel consumers
of fpu_kern KPI both on i386 and amd64.
First version of the support for AVX was submitted by Tim Bird
<tim.bird am sony com> on behalf of Sony. This version was written
from scratch.
Tested by: pho (previous version), Yamagi Burmeister <lists yamagi org>
MFC after: 1 month
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