1 2 /* This is really horrible. It checks that the 3 stack unwinder understands DW_CFA_def_cfa_expression. It is 4 the result of compiling this: 5 6 void bbb ( long x ) 7 { 8 __asm__ __volatile__( 9 "cmp %0,%0\n\t" 10 "jz .Lxyzzy\n" 11 ".Lxyzzy:\n\t" 12 : : "r"(x) : "cc" 13 ); 14 } 15 16 void aaa ( long x ) { 17 bbb(x); 18 } 19 20 int main ( void ) 21 { 22 long *p = malloc(8); 23 aaa( *p ); 24 return 0; 25 } 26 27 and bracketing the cmp/jz insns with a move down/up by 256 of %rsp. 28 The .jz causes memcheck to complain, hence unwind the stack, but 29 that cannot be successfully done unless the return address can 30 be found. Hence the handwritten CFI below uses 31 DW_CFA_def_cfa_expression to make that possible. 32 33 The CFI below isn't really right in that aaa appears twice 34 in the backtrace 35 36 ==12868== Conditional jump or move depends on uninitialised value(s) 37 ==12868== at 0x400512: bbb (in /home/sewardj/VgTRUNK/trunk/mad0) 38 ==12868== by 0x400520: aaa (in /home/sewardj/VgTRUNK/trunk/mad0) 39 ==12868== by 0x400520: aaa (in /home/sewardj/VgTRUNK/trunk/mad0) 40 ==12868== by 0x400538: main (in /home/sewardj/VgTRUNK/trunk/mad0) 41 42 but GDB behaves the same, so I'm not too concerned - indicates 43 the problem is with the handwritten CFI and not with 44 V's interpretation of it. 45 */ 46 47 48 .file "bad0.c" 49 .text 50 51 52 .globl bbb 53 .type bbb, @function 54 bbb: 55 .LFB2: 56 .Lbbb1: 57 subq $256,%rsp 58 .Lbbb2: 59 cmp %rdi,%rdi 60 jz .Lxyzzy 61 .Lxyzzy: 62 addq $256,%rsp 63 .Lbbb3: 64 ret 65 .Lbbb4: 66 .LFE2: 67 .size bbb, .-bbb 68 69 70 71 .globl aaa 72 .type aaa, @function 73 aaa: 74 .LFB3: 75 call bbb 76 rep ; ret 77 .LFE3: 78 .size aaa, .-aaa 79 .globl main 80 .type main, @function 81 main: 82 .LFB4: 83 subq $8, %rsp 84 .LCFI0: 85 movl $8, %edi 86 call malloc 87 movq (%rax), %rdi 88 call aaa 89 movl $0, %eax 90 addq $8, %rsp 91 ret 92 .LFE4: 93 .size main, .-main 94 .section .eh_frame,"a",@progbits 95 .Lframe1: 96 .long .LECIE1-.LSCIE1 97 .LSCIE1: 98 .long 0x0 99 .byte 0x1 100 .string "zR" 101 .uleb128 0x1 102 .sleb128 -8 103 .byte 0x10 104 .uleb128 0x1 105 .byte 0x3 106 .byte 0xc 107 .uleb128 0x7 108 .uleb128 0x8 109 .byte 0x90 110 .uleb128 0x1 111 .align 8 112 .LECIE1: 113 114 /* start of the FDE for bbb */ 115 .LSFDE1: 116 .long .LEFDE1-.LASFDE1 /* length of FDE */ 117 .LASFDE1: 118 .long .LASFDE1-.Lframe1 /* CIE pointer */ 119 .long .LFB2 /* & bbb */ 120 .long .LFE2-.LFB2 /* sizeof(bbb) */ 121 .uleb128 0 /* augmentation length */ 122 .byte 0x40 + .Lbbb2 - .Lbbb1 /* _advance_loc to .Lbbb2 */ 123 124 /* For the section in between .Lbbb2 and .Lbbb3, set the 125 CFA to be %rsp+256, and set the return address (dwarf r16) 126 to be *(CFA+0). */ 127 .byte 0x0f /* _def_cfa_expression */ 128 .uleb128 .Lexpr1e-.Lexpr1s /* length of expression */ 129 .Lexpr1s: 130 .byte 0x77 /* DW_OP_breg7 == %rsp + sleb128(0) */ 131 .sleb128 0 132 .byte 0x40 /* DW_OP_lit16 */ 133 .byte 0x40 /* DW_OP_lit16 */ 134 .byte 0x1e /* DW_OP_mul */ 135 .byte 0x22 /* DW_OP_plus */ 136 .Lexpr1e: 137 .byte 0x90 /* _cfa_offset: r16 = *(cfa+0) */ 138 .uleb128 0 139 140 .byte 0x40 + .Lbbb3 - .Lbbb2 /* _advance_loc to .Lbbb3 */ 141 142 /* For the section .Lbbb3 to .Lbbb4, should set CFA back to 143 something sensible. This tries to do it but still causes 144 GDB to show an extraneous aaa frame on the stack. Oh well. */ 145 /* Now set CFA back to %rsp+0 */ 146 .byte 0x0f /* _def_cfa_expression */ 147 .uleb128 .Lexpr2e-.Lexpr2s /* length of expression */ 148 .Lexpr2s: 149 .byte 0x77 /* DW_OP_breg7 == %rsp + sleb128(0) */ 150 .sleb128 0 151 .byte 0x30 /* DW_OP_lit0 */ 152 .byte 0x1c /* DW_OP_minus */ 153 .Lexpr2e: 154 .byte 0x90 /* _cfa_offset: r16 = *(cfa+0) */ 155 .uleb128 0 156 157 .byte 0x40 + .Lbbb4 - .Lbbb3 /* _advance_loc to .Lbbb4 */ 158 .uleb128 0x0 /* ??? */ 159 .align 8 160 .LEFDE1: 161 /* end of the FDE for bbb */ 162 163 .LSFDE3: 164 .long .LEFDE3-.LASFDE3 165 .LASFDE3: 166 .long .LASFDE3-.Lframe1 167 .long .LFB3 168 .long .LFE3-.LFB3 169 .uleb128 0x0 170 .align 8 171 .LEFDE3: 172 .LSFDE5: 173 .long .LEFDE5-.LASFDE5 174 .LASFDE5: 175 .long .LASFDE5-.Lframe1 176 .long .LFB4 177 .long .LFE4-.LFB4 178 .uleb128 0x0 179 .byte 0x4 180 .long .LCFI0-.LFB4 181 .byte 0xe 182 .uleb128 0x10 183 .align 8 184 .LEFDE5: 185 .ident "GCC: (GNU) 4.1.2 20061115 (prerelease) (SUSE Linux)" 186 .section .note.GNU-stack,"",@progbits 187
