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- /*
- * this is the internal transfer function.
- *
- * HISTORY
- * 07-Sep-16 Add clang support using x register naming. Fredrik Fornwall
- * 13-Apr-13 Add support for strange GCC caller-save decisions
- * 08-Apr-13 File creation. Michael Matz
- *
- * NOTES
- *
- * Simply save all callee saved registers
- *
- */
-
- #define STACK_REFPLUS 1
-
- #ifdef SLP_EVAL
- #define STACK_MAGIC 0
- #define REGS_TO_SAVE "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26", \
- "x27", "x28", "x30" /* aka lr */, \
- "v8", "v9", "v10", "v11", \
- "v12", "v13", "v14", "v15"
-
- static int
- slp_switch(void)
- {
- int err;
- void *fp;
- register long *stackref, stsizediff;
- __asm__ volatile ("" : : : REGS_TO_SAVE);
- __asm__ volatile ("str x29, %0" : "=m"(fp) : : );
- __asm__ ("mov %0, sp" : "=r" (stackref));
- {
- SLP_SAVE_STATE(stackref, stsizediff);
- __asm__ volatile (
- "add sp,sp,%0\n"
- "add x29,x29,%0\n"
- :
- : "r" (stsizediff)
- );
- SLP_RESTORE_STATE();
- /* SLP_SAVE_STATE macro contains some return statements
- (of -1 and 1). It falls through only when
- the return value of slp_save_state() is zero, which
- is placed in x0.
- In that case we (slp_switch) also want to return zero
- (also in x0 of course).
- Now, some GCC versions (seen with 4.8) think it's a
- good idea to save/restore x0 around the call to
- slp_restore_state(), instead of simply zeroing it
- at the return below. But slp_restore_state
- writes random values to the stack slot used for this
- save/restore (from when it once was saved above in
- SLP_SAVE_STATE, when it was still uninitialized), so
- "restoring" that precious zero actually makes us
- return random values. There are some ways to make
- GCC not use that zero value in the normal return path
- (e.g. making err volatile, but that costs a little
- stack space), and the simplest is to call a function
- that returns an unknown value (which happens to be zero),
- so the saved/restored value is unused. */
- __asm__ volatile ("mov %0, #0" : "=r" (err));
- }
- __asm__ volatile ("ldr x29, %0" : : "m" (fp) :);
- __asm__ volatile ("" : : : REGS_TO_SAVE);
- return err;
- }
-
- #endif
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