Hi Gabe, On Wed, Nov 9, 2011 at 9:34 AM, Gabe Black <gabebl...@chromium.org> wrote: > When gcc compiles some 64 bit operations on a 32 bit machine, it generates > calls to small functions instead of instructions which do the job directly. > Those functions are defined in libgcc and transparently provide whatever > functionality was necessary. Unfortunately, u-boot can be built with a > non-standard ABI when libgcc isn't. More specifically, u-boot uses > -mregparm. When the u-boot and libgcc are linked together, very confusing > bugs can crop up, for instance seemingly normal integer division or modulus > getting the wrong answer or even raising a spurious divide by zero > exception. > > This change barrows (steals) a technique and some code from coreboot which > solves this problem by creating wrappers which translate the calling > convention when calling the functions in libgcc. Unfortunately that means that > these instructions which had already been turned into functions have even more > overhead, but more importantly it makes them work properly. > > To find all of the functions that needed wrapping, u-boot was compiled without > linking in libgcc. All the symbols the linker complained were undefined were > presumed to be the symbols that are needed from libgcc. These were a subset of > the symbols covered by the coreboot code, so it was used unmodified. > > Signed-off-by: Gabe Black <gabebl...@chromium.org> > --- > Changes in v2: > - Change the [x86] tag to x86: > - Mention -mregparm in the commit message. > - Get rid of a stray line which snuck in during a rebase.
As mentioned in a reply to 'Import the glibc memset implementation', I think I would prefer to either: - Investigate if regparm usage can be dropped so U-Boot is ABI compliant - If not, use USE_PRIVATE_LIBGCC and implement all required libgcc functions in U-Boot Either way, I don't want to have the possibility that someone uses another libgcc function, forgets to put a wrapper around it, and encounter 'weird' bugs Regards, Graeme _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
