1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Symbols calculate_checksums() must not give an entry of their own. 4 * 5 * Three kinds are skipped, for two different reasons: 6 * 7 * zero-length there is nothing to hash, and an entry keyed on the 8 * symbol's address would collide with whatever really lives 9 * there. 10 * alias a second name for an address already checksummed. 11 * cold part hashed as part of its parent, which func_for_each_insn() 12 * walks into, so a separate entry would double-count it. 13 * 14 * An entry per address is the invariant: .discard.sym_checksum is looked up by 15 * the address a relocation points at, so two entries for one address make the 16 * lookup ambiguous and one of the two checksums unreachable. 17 */ 18 19 static const char __modinfo[] 20 __attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux"; 21 22 /* Zero-length: an object symbol of size 0, in a section of its own. */ 23 extern char empty_marker[]; 24 __asm__(".pushsection .data.empty_marker,\"aw\",@progbits\n" 25 ".globl empty_marker\n" 26 ".type empty_marker, @object\n" 27 "empty_marker:\n" 28 ".size empty_marker, 0\n" 29 ".popsection\n"); 30 31 int real_function(int x); 32 int real_function(int x) 33 { 34 #ifdef PATCHED 35 return x + 2; 36 #else 37 return x + 1; 38 #endif 39 } 40 41 /* Alias: a second name for real_function's address. */ 42 int alias_function(int x) __attribute__((alias("real_function"))); 43 44 int target(int x) 45 { 46 return real_function(x) + alias_function(x) + (int)(long)empty_marker; 47 } 48