pwmgen: prevent GCC from emitting SSE in base-thread function#3896
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grandixximo wants to merge 1 commit intoLinuxCNC:masterfrom
Open
pwmgen: prevent GCC from emitting SSE in base-thread function#3896grandixximo wants to merge 1 commit intoLinuxCNC:masterfrom
grandixximo wants to merge 1 commit intoLinuxCNC:masterfrom
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make_pulses() is exported with uses_fp=0 for the base-thread, but GCC
optimizes struct zeroing into SSE instructions (pxor/movups on XMM
registers). Since RTAI skips FPU/SSE save/restore for non-FP threads,
this silently corrupts XMM state of whatever Linux process was running,
causing heap corruption, segfaults, and hard crashes.
Add __attribute__((target("general-regs-only"))) to make_pulses() to
force GCC to use only general-purpose registers.
Confirmed via objdump that the compiled function contains zero SSE
instructions after this change. Tested on RTAI 5.4.280 with the
etch-servo parport config which previously crashed reliably.
See: LinuxCNC#3895
Collaborator
|
Is this fix still needed, or are we going for the meta-fix? |
Author
|
I can work on ripping out non-FP in the weekend, this will not be needed once that is done, it is just a quick fix, if anyone wants to run RTAI with pwmgen in the meantime, Though I doubt there is anyone else but me testing this. |
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make_pulses() is exported with uses_fp=0 for the base-thread, but GCC optimizes struct zeroing into SSE instructions (pxor/movups on XMM registers). Since RTAI skips FPU/SSE save/restore for non-FP threads, this silently corrupts XMM state of whatever Linux process was running, causing heap corruption, segfaults, and hard crashes.
Add attribute((target("general-regs-only"))) to make_pulses() to force GCC to use only general-purpose registers.
Confirmed via objdump that the compiled function contains zero SSE instructions after this change. Tested on RTAI 5.4.280 with the etch-servo parport config which previously crashed reliably.
See: #3895