FFI Symbol Resolution and Dynamic Linking
When you use PHP's Foreign Function Interface (FFI) to interact with C libraries, one of the most critical steps is symbol resolution. A symbol is the name of a function, variable, or object as it appears in a shared library, typically a .so (on Linux) or .dll (on Windows) file. PHP FFI must locate these symbols at runtime so that your PHP code can call C functions as if they were native PHP functions.
The process begins when you use FFI::cdef() to declare the C function signatures you want to use. PHP then loads the specified shared library into memory. This is done using platform-specific dynamic linker mechanisms: dlopen() on Unix-like systems or LoadLibrary() on Windows. Once the library is loaded, FFI parses the C declarations and attempts to resolve each symbol name to an actual function or variable address within the shared library.
For each declared function, FFI uses the symbol name to search the library's symbol table. If it finds a matching symbol, it retrieves a function pointer to that address. PHP then creates a callable PHP object that, when invoked, calls the underlying C function through this pointer. This mapping is dynamic—no static linking is required at compile time, so you can swap libraries or update function implementations without recompiling PHP itself.
main.php
1234567891011<?php // Load the standard C library and call the 'strlen' function $ffi = FFI::cdef( "size_t strlen(const char *s);", PHP_OS_FAMILY === "Windows" ? "msvcrt.dll" : "libc.so.6" ); $str = "Hello, FFI!"; $length = $ffi->strlen($str); echo "Length: $length\n"; ?>
While FFI's dynamic linking is powerful, it is not without pitfalls. If the specified shared library cannot be found—perhaps due to a missing file, incorrect path, or incompatible architecture, PHP will throw an exception at the moment FFI::cdef() is called. Similarly, if a declared symbol such as a function name does not exist in the loaded library, FFI will raise an error when you attempt to access or call that function. These errors are typically FFI\Exception or FFI\ParserException and can be caught using standard PHP exception handling.
It is important to ensure that the library you are loading contains all the required symbols, and that you are using the correct library version for your operating system and hardware. FFI does not provide compile-time checks, so all symbol resolution happens at runtime, making robust error handling essential for production code.
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When you use PHP's Foreign Function Interface (FFI) to interact with C libraries, one of the most critical steps is symbol resolution. A symbol is the name of a function, variable, or object as it appears in a shared library, typically a .so (on Linux) or .dll (on Windows) file. PHP FFI must locate these symbols at runtime so that your PHP code can call C functions as if they were native PHP functions.
The process begins when you use FFI::cdef() to declare the C function signatures you want to use. PHP then loads the specified shared library into memory. This is done using platform-specific dynamic linker mechanisms: dlopen() on Unix-like systems or LoadLibrary() on Windows. Once the library is loaded, FFI parses the C declarations and attempts to resolve each symbol name to an actual function or variable address within the shared library.
For each declared function, FFI uses the symbol name to search the library's symbol table. If it finds a matching symbol, it retrieves a function pointer to that address. PHP then creates a callable PHP object that, when invoked, calls the underlying C function through this pointer. This mapping is dynamic—no static linking is required at compile time, so you can swap libraries or update function implementations without recompiling PHP itself.
main.php
1234567891011<?php // Load the standard C library and call the 'strlen' function $ffi = FFI::cdef( "size_t strlen(const char *s);", PHP_OS_FAMILY === "Windows" ? "msvcrt.dll" : "libc.so.6" ); $str = "Hello, FFI!"; $length = $ffi->strlen($str); echo "Length: $length\n"; ?>
While FFI's dynamic linking is powerful, it is not without pitfalls. If the specified shared library cannot be found—perhaps due to a missing file, incorrect path, or incompatible architecture, PHP will throw an exception at the moment FFI::cdef() is called. Similarly, if a declared symbol such as a function name does not exist in the loaded library, FFI will raise an error when you attempt to access or call that function. These errors are typically FFI\Exception or FFI\ParserException and can be caught using standard PHP exception handling.
It is important to ensure that the library you are loading contains all the required symbols, and that you are using the correct library version for your operating system and hardware. FFI does not provide compile-time checks, so all symbol resolution happens at runtime, making robust error handling essential for production code.
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