as usual, I have something to add few minutes after I've sent the mail... :-)
On Mon, 2007-12-31 at 10:33 +0100, Herbert Valerio Riedel wrote: [..] > which when compiled with 4.2.3 20071123 (prerelease) (Debian 4.2.2-4), > causes a segfault when using -O2, but works when either removing the > 'static' modifier and thus avoiding inlining of do_segfault, or by using > an optimization level which does avoid that... > > the generated assembler code is quite broken for the optimized case: > > (I've only pasted and commented the relevant section containing the 5 > nops) > > // r4 points to outbuf (= source buffer) > // sp points to inbuf (= target buffer) > #APP > nop > mov r2, sp > add r1, sp, #56 // upper loop-bound; should have been #12 I actually wanted to say 'should have been #24' :-) this overrun is what causes the segfault... and which goes away when not inlining, but the source-ptr not updating... > cmp r4, r1 // upper loop-bound check > add r2, r2, #2 // increment target buffer (NB: source buffer is > not incremented!) > bne .L2 // repeat loop if upper loop-bound not reached yet ...stays even when avoiding inlining; it's somehow the optimizer that gets confused by in_buf[2*i] = ( out_buf[2*i] | out_buf[(2*i)+1]<<8 ) & 0xFF; in_buf[(2*i)+1] = ( out_buf[2*i] | out_buf[(2*i)+1]<<8 ) >> 8; which gcc correctly optimizes to in_buf[2*i] = out_buf[2*i]; in_buf[(2*i)+1] = out_buf[(2*i)+1]; but then gets confused; if one takes away that confusion from gcc by replacing the former two lines by their latter equivalent optimized variants, code generation is fine for all optimization levels... cheers, hvr -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
