116 lines
2.5 KiB
C
116 lines
2.5 KiB
C
/* vim: tabstop=4 shiftwidth=4 noexpandtab
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*
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* FPU and SSE context handling.
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*
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* FPU context is kept through context switches,
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* but the FPU is disabled. When an FPU instruction
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* is executed, it will trap here and the context
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* will be saved to its original owner and the context
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* for the current process will be loaded or the FPU
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* will be reset for the new process.
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*
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* FPU states are per kernel thread.
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*
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*/
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#include <system.h>
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#include <logging.h>
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process_t * fpu_thread = NULL;
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/**
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* Set the FPU control word
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*
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* @param cw What to set the control word to.
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*/
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void
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set_fpu_cw(const uint16_t cw) {
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asm volatile("fldcw %0" :: "m"(cw));
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}
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/**
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* Enable the FPU and SSE
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*/
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void enable_fpu(void) {
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asm volatile ("clts");
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size_t t;
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asm volatile ("mov %%cr4, %0" : "=r"(t));
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t |= 3 << 9;
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asm volatile ("mov %0, %%cr4" :: "r"(t));
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}
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/**
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* Disable FPU and SSE so it traps to the kernel
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*/
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void disable_fpu(void) {
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size_t t;
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asm volatile ("mov %%cr0, %0" : "=r"(t));
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t |= 1 << 3;
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asm volatile ("mov %0, %%cr0" :: "r"(t));
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}
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/* Temporary aligned buffer for copying around FPU contexts */
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uint8_t saves[512] __attribute__((aligned(16)));
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/**
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* Restore the FPU for a process
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*/
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void restore_fpu(process_t * proc) {
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memcpy(&saves,(uint8_t *)&proc->thread.fp_regs,512);
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asm volatile ("fxrstor %0" : "=m"(saves));
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}
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/**
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* Save the FPU for a process
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*/
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void save_fpu(process_t * proc) {
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asm volatile ("fxsave %0" : "=m"(saves));
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memcpy((uint8_t *)&proc->thread.fp_regs,&saves,512);
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}
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/**
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* Initialize the FPU
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*/
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void init_fpu(void) {
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asm volatile ("fninit");
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set_fpu_cw(0x37F);
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}
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/**
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* Kernel trap for FPU usage when FPU is disabled
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*/
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void invalid_op(struct regs * r) {
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/* First, turn the FPU on */
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enable_fpu();
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if (fpu_thread == current_process) {
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/* If this is the tread that last used the FPU, do nothing */
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return;
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}
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if (fpu_thread) {
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/* If there is a thread that was using the FPU, save its state */
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save_fpu(fpu_thread);
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}
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fpu_thread = (process_t *)current_process;
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if (!fpu_thread->thread.fpu_enabled) {
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/*
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* If the FPU has not been used in this thread previously,
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* we need to initialize it.
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*/
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init_fpu();
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fpu_thread->thread.fpu_enabled = 1;
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return;
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}
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/* Otherwise we restore the context for this thread. */
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restore_fpu(fpu_thread);
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}
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/* Called during a context switch; disable the FPU */
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void switch_fpu(void) {
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disable_fpu();
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}
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/* Enable the FPU context handling */
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void fpu_install(void) {
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isrs_install_handler(6, &invalid_op);
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isrs_install_handler(7, &invalid_op);
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}
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