$ cat > test.c #include <stdlib.h> void *f(int flag) { return flag ? malloc(1) : NULL; } $ gcc -S -O3 -fomit-frame-pointer -fPIC -DPIC test.c -o - .file "test.c" .text .p2align 4,,15 .globl f .type f, @function f: pushl %ebx pushl %eax call .L3 .L3: popl %ebx addl $_GLOBAL_OFFSET_TABLE_+[.-.L3], %ebx pushl %eax movl 16(%esp), %edx testl %edx, %edx je .L2 subl $12, %esp pushl $1 call malloc@PLT addl $16, %esp .L1: popl %edx popl %ecx popl %ebx ret .p2align 4,,7 .L2: xorl %eax, %eax jmp .L1 .size f, .-f .section .note.GNU-stack,"",@progbits .ident "GCC: (GNU) 3.3.3 20040412 (ALT Linux, build 3.3.3-alt5)" It's clearly visible that check if flag is equal to 0 performed after loading address of _GLOBAL_OFFSET_TABLE_ in %ebx. It would be more effective to perform this check before loading GOT in %ebx.
still in gcc3.4
Same with gcc-4.1.1; maybe I should report it upstream? :)
Ой что я нашёл :) #6052 сюда же.
$ gcc -S -O3 -fomit-frame-pointer -fPIC -DPIC test.c -o - .file "test.c" .text .p2align 4,,15 .globl f .type f, @function f: .LFB12: .cfi_startproc testl %edi, %edi jne .L4 xorl %eax, %eax ret .p2align 4,,10 .p2align 3 .L4: movl $1, %edi jmp malloc@PLT .cfi_endproc .LFE12: .size f, .-f .ident "GCC: (GNU) 4.5.1 20100924 (ALT Linux 4.5.1-alt1)" .section .note.GNU-stack,"",@progbits It seems fixed in gcc4.5.
