Le 03/10/2010 01:07, Graeme Russ a écrit : > On 03/10/10 08:09, Albert ARIBAUD wrote: >> Le 02/10/2010 22:39, Reinhard Meyer a écrit : >> >>> And as an idea, if position independent code is used, only pointers >>> in initialized data need adjustment. Cannot the linker emit a table >>> of addresses that need fixing? >> >> IIU Bill C, yes the linker can emit the information and the startup code >> could use this information instead of relying on hand-provided info; the >> linker file probably needs to be modified in order to provide such info. >> I intend to look into this, but feel free to do too. > > As mentioned previously, I have already done this for x86. The linker flags > used are -pic and --emit-relocs. The linker produces a section named > rel.dyn which needs to be processed but not loaded into RAM. rel.dyn > contains a simple list of address (within .text, .data, .rodata etc) each > of which need a simple adjustment equal to the relocation offset.
Bill just said that -pic (or, for ARM, -fPIC or -fPIE) was unnecessary for relocation. You seem to imply it actually is... In my experience, -fPIC and-fPIE do increase code by adding GOT relocation to symbols that need fixing, so they would indeed be redundant to any other relocation mechanism -- I just did some test with basic code and this seems to confirm, no -fPIx is needed to get relocation the way you do on ARM. > The size increase of the code + data loaded into RAM is 104012 bytes to > 104296 bytes which is only 284 bytes or a mere 0.3% (which is negligible) > with an additional 22424 bytes in rel.dyn (22%) not loaded into RAM > > The additional bonus is that .got is not referenced during run-time, so > there is no run-time performance penalty. However, the penalty of > processing 2803 relocation records at startup may not be wholly recovered > during a typical u-boot run-time session. > > All this is for x86, and may not apply so neatly to other arches Of course. :) Amicalement, -- Albert. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
