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| H A D | ptrace_machdep.c | diff 238669 Sat Jul 21 11:13:07 MDT 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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