| 1 | #include <asm/hwcap.h> |
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| 2 | #include <stdint.h> |
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| 3 | #include <sys/auxv.h> |
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| 4 | |
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| 5 | #ifndef HWCAP2_FPMR |
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| 6 | #define HWCAP2_FPMR (1UL << 48) |
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| 7 | #endif |
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| 8 | |
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| 9 | uint64_t get_fpmr(void) { |
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| 10 | uint64_t fpmr = 0; |
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| 11 | __asm__ volatile("mrs %0, s3_3_c4_c4_2" : "=r" (fpmr)); |
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| 12 | return fpmr; |
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| 13 | } |
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| 14 | |
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| 15 | void set_fpmr(uint64_t value) { |
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| 16 | __asm__ volatile("msr s3_3_c4_c4_2, %0" ::"r" (value)); |
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| 17 | } |
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| 18 | |
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| 19 | // Set F8S1 (bits 0-2) and LSCALE2 (bits 37-32) (to prove we treat fpmr as 64 |
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| 20 | // bit). |
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| 21 | const uint64_t original_fpmr = (uint64_t)0b101010 << 32 | (uint64_t)0b101; |
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| 22 | |
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| 23 | void expr_func() { set_fpmr(original_fpmr); } |
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| 24 | |
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| 25 | int main(int argc, char *argv[]) { |
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| 26 | if (!(getauxval(AT_HWCAP2) & HWCAP2_FPMR)) |
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| 27 | return 1; |
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| 28 | |
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| 29 | // As FPMR controls a bunch of floating point options that are quite |
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| 30 | // extensive, we're not going to run any floating point ops here. Instead just |
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| 31 | // update the value from the debugger and check it from this program, and vice |
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| 32 | // versa. |
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| 33 | set_fpmr(original_fpmr); |
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| 34 | |
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| 35 | // Here the debugger checks it read back the value above, then writes in a new |
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| 36 | // value. Note that the bits are flipped in the new value. |
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| 37 | uint64_t new_fpmr = get_fpmr(); // Set break point at this line. |
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| 38 | uint64_t expected_fpmr = ((uint64_t)0b010101 << 32) | (uint64_t)0b010; |
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| 39 | |
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| 40 | // If the debugger failed to update the value, exit uncleanly. |
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| 41 | // This also allows you to run this program standalone to create a core file. |
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| 42 | if (new_fpmr != expected_fpmr) |
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| 43 | __builtin_trap(); |
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| 44 | |
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| 45 | return 0; |
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| 46 | } |
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| 47 | |
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