On Jan 30, 2011, at 3:57 PM, Jonathan Wakely wrote: > On 30 January 2011 20:45, Amittai Aviram wrote: >> On this GCC Internals page >> >> http://en.wikibooks.org/wiki/GNU_C_Compiler_Internals/GNU_C_Compiler_Architecture_3_4 >> >> I found the following in the "GCC Initialization" section: >> >> "GCC built-in functions are the functions that are evaluated at compile time. For example, if the size argument of a strcpy() function is a constant then GCC replaces the function call with the required number of assignments." >> >> I was curious about this, so I tried compiling to assembly (-S) a very simple program: >> >> #include <stdio.h> >> #include <stdlib.h> >> #include <string.h> >> >> int main(void) { >> >> char s1[0x10]; >> char * s0 = "HELLO"; >> strcpy(s1, s0); >> printf("%s %s\n", s0, s1); >> return EXIT_SUCCESS; >> } >> >> But the resulting assembly code simply calls strcpy with the two arguments, just as I would have expected had I not read the above sentence: >> >> movq $.LC0, -40(%rbp) >> movq -40(%rbp), %rdx >> leaq -32(%rbp), %rax >> movq %rdx, %rsi >> movq %rax, %rdi >> call strcpy >> >> (Here, .LC0 labels the string "HELLO".) >> >> So what does that sentence actually mean and what am I missing? Thanks! > > strcpy has no 'size' parameter, I assume it's meant to say strncpy I tried it with strncpy and with __builtin_strncpy, with exactly the same results, i.e., the assembly code still calls strncpy with three arguments. Amittai Aviram PhD Student in Computer Science Yale University 646 483 2639 amittai.aviram@xxxxxxxx http://www.amittai.com
