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On Thu, Feb 26, 2004 at 03:21:39PM -0800, Andrew Morton wrote: > Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> wrote: > > > > I compile my kernels for 486 but buils system aligns > > functions and labels to 16 bytes, with results like this: > > > > 00000730 <islpci_eth_tx_timeout>: > > 730: 55 push %ebp > > 731: 89 e5 mov %esp,%ebp > > 733: 8b 45 08 mov 0x8(%ebp),%eax > > 736: 8b 40 64 mov 0x64(%eax),%eax > > 739: 05 14 03 00 00 add $0x314,%eax > > 73e: ff 40 14 incl 0x14(%eax) > > 741: 5d pop %ebp > > 742: c3 ret > > 743: 90 nop > > 744: 90 nop > > 745: 90 nop > > 746: 90 nop > > 747: 90 nop > > 748: 90 nop > > 749: 90 nop > > 74a: 90 nop > > 74b: 90 nop > > 74c: 90 nop > > 74d: 90 nop > > 74e: 90 nop > > 74f: 90 nop > > > > Losing on average 15/2 bytes to alignment, my kernel lose > > # echo $((`cat System.map | grep '0 ' | wc -l`*15/2)) > > 149632 > > bytes only due to function alignment, not counting jump target > > alighment. > > > > Is there any way to prevent this? > > Yes, there are ways of turning off a lot of this alignment padding and it > makes a significant different in code size. You need to dig around in the > gcc documentation for the several -*align* options. > > IIRC, not all of the padding could be turned off (the gcc options were not > complete) but it's a couple of years since I investigated this. Denis, there's a patch in -tiny to let you experiment with overriding CFLAGS. See http://selenic.com/tiny-about/ You probably want something like: -falign-functions=1 -falign-jumps=1 -falign-labels=1 -falign-loops=1 -- Matt Mackall : http://www.selenic.com : Linux development and consulting - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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