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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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a90271c6af
Split userland/arch/<arch>/c/ into inline_asm and intrinsics, and move programs that don't match either up.
40 lines
1007 B
C
40 lines
1007 B
C
/* https://github.com/cirosantilli/linux-kernel-module-cheat#arm-calling-convention */
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#include <assert.h>
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#include <inttypes.h>
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uint64_t my_asm_func(void);
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/* { return 42; } */
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__asm__(
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".global my_asm_func;"
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"my_asm_func:"
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"mov x0, 42;"
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"ret;"
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);
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/* Now a more complex example that also calls a C function.
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* We have to store the return value x30 for later because bl modifies it.
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* https://stackoverflow.com/questions/27941220/push-lr-and-pop-lr-in-arm-arch64/34504752#34504752
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* We are not modifying any other callee saved register in this function,
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* since my_c_func is not either (unless GCC has a bug ;-)), so everything else if fine.
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*/
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uint64_t my_asm_func_2(void);
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/* { return my_c_func(); } */
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__asm__(
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".global my_asm_func_2;"
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"my_asm_func_2:"
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"str x30, [sp, -16]!;"
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"bl my_c_func;"
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"ldr x30, [sp], 16;"
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"ret;"
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);
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uint64_t my_c_func(void) {
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return 42;
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}
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int main(void) {
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assert(my_asm_func() == 42);
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assert(my_asm_func_2() == 42);
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}
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