On 27 December 2015 at 21:34, Ard Biesheuvel <[email protected]> wrote: > On 27 December 2015 at 20:14, Leif Lindholm <[email protected]> wrote: >> On Sun, Dec 27, 2015 at 08:02:34PM +0100, Ard Biesheuvel wrote: >>> On 27 December 2015 at 18:58, Leif Lindholm <[email protected]> >>> wrote: >>> > On Thu, Dec 24, 2015 at 02:03:16PM +0100, Ard Biesheuvel wrote: >>> >> The tiny code model for AARCH64 is the most efficient model, since its >>> >> symbol references are relative via a single 32-bit ADR instruction. This >>> >> gives us a range of only +/- 1 MB, but this is sufficient for the vast >>> >> majority of the modules that make up a typical EDK2 firmware. Since the >>> >> reference is relative, it does not result in a fixup entry in the PE/COFF >>> >> relocation table. Unlike the small code model, which uses ADRP >>> >> instructions, >>> >> the tiny model does not impose section alignment requirements. >>> >> >>> >> However, in some cases, (e.g., the full Shell binary built in DEBUG mode) >>> >> the resulting binary exceeds 1 MB, which may result in build errors if >>> >> code at one end of the image references a symbol at the other end. >>> >> >>> >> Since the tiny and small code models can coexist in a single binary, we >>> >> can work around this problem by making sure that tiny model .text and >>> >> .data sections are emitted in close proximity to each other, by reducing >>> >> the function alignment for tiny model code (which by itself should also >>> >> be >>> >> an improvement in terms of code size), and sorting the linker input by >>> >> alignment. >>> > [...] >>> > My GCC manpage claims that >>> > "-Os disables the following optimization flags: -falign-functions ..." >>> > and -Os is set in GCC_ALL_CC_FLAGS, and as far as I can see not >>> > overridden for AARCH64, except for DEBUG builds. >>> > >>> >>> OK, that means we will need to build the RELEASE Shell components with >>> -O2 rather than -Os if we ever hit the same issue for RELEASE builds. >>> Since those modules are not the ones where we are likely to care >>> deeply about code size, this is not a showstopper I think >> >> Could we move the -falign-functions=4 to DEBUG_GCCnn_AARCH64_CC_FLAGS >> instead then, next to the -O0? I'd prefer keeeping dead parameters off >> the command line where possible. >> >> Of course, could make sense to change the DEBUG_GCCnn_AARCH64_CC_FLAGS >> to include a common DEBUG_GCC_AARCH64_CC_FLAGS variable where these >> are set instead. >> > > Well, since this applies to GCC49 DEBUG only, let's add it only there > instead. GCC49 currently means '4.9 or later', and I hope we will not > have a need to introduce GCC5 etc, and if that does happen, let's > worry about it then. >
I double checked this, and it turns out that -Os implies -falign-functions=4, so while it does disable it usually, it does not in this particular case. I will still move it to the DEBUG flags, though, since that is the only place we need it. _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
