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authorKieran Bingham <kieran.bingham@ideasonboard.com>2020-02-18 12:51:14 +0000
committerKieran Bingham <kieran.bingham@ideasonboard.com>2020-02-19 10:21:21 +0000
commit90240a79506a3c400f3af4cb0b08746ae87c79e2 (patch)
treef71cf819bb96187e5ddb2aaed7d8da71ce02e674 /Documentation/theme/layout.html
parentb5eff18f1aef980fa7eb55184996710a6fc9523e (diff)
libcamera: media_device: prevent sign extension on casts
The conversion of pointers to integers is implementation defined and differs between g++ and clang++ when utilising a uint64_t type. #include <iostream> int main(int argc, char **argv) { void *ptr = reinterpret_cast<void *>(0xf1234567); uint64_t u64 = reinterpret_cast<uint64_t>(ptr); uint64_t uint64 = reinterpret_cast<uintptr_t>(ptr); std::cout << "ptr " << ptr << " ptr -> u64 0x" << std::hex << u64 << " ptr -> uintptr_t -> u64 0x" << std::hex << uint64 << std::endl; return 0; } When compiled with g++ for a 32-bit platform produces the following unexpected output: ptr 0xf1234567 ptr -> u64 0xfffffffff1234567 ptr -> uintptr_t -> u64 0xf1234567 The standards states: "A pointer can be explicitly converted to any integral type large enough to hold all values of its type. The mapping function is implementation-defined. [Note: It is intended to be unsurprising to those who know the addressing structure of the underlying machine. — end note]" And as such the g++ implementation appears to be little more surprising than expected in this situation. The MediaDevice passes pointers to the kernel via the struct media_v2_topology in which pointers are cast using a uint64 type (__u64), which is affected by the sign extension described above when BIT(32) is set and causes an invalid address to be given to the kernel. Ensure that we cast using uintptr_t which is not affected by the sign extension issue. Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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