Messages in this thread | | | Date | Thu, 23 Nov 2017 14:01:44 +0200 (EET) | From | Martin Storsjö <> | Subject | Re: [PATCH v2] arm: detect buggy binutils when in thumb2 mode |
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On Thu, 23 Nov 2017, Jason A. Donenfeld wrote:
> On older versions of binutils, \sym points to an aligned address. On > newer versions of binutils, \sym sometimes points to the unaligned thumb > address in certain circumstances. In order to homogenize this behavior, > rather than adding 1, we could simply OR in 1, so that already unaligned > instructions don't change. While that works, the downside is that we have > to add an `orr` instruction to a fast path. The assembler can't do this at > assemble time via "|1" because "invalid operands (.text and *ABS* sections) > for `|'". A better solution would be to have consistent binutils behavior, > but that ship has sailed. > > So, this commit adds a detection mechanism, which began as a small thing > from Russell King that I then rewrote to use pure bash instead of > shelling out, so that it doesn't slow down the build process. The detection > mechanism _could_ be used to modify the assembly we generate, but for now > it's just being used to catch buggy binutils and abort the build process in > that case. > > The rest of this commit message contains all of the relevant information > about the boot bug when compiled in thumb2 mode. > > My tests concerned these versions: > broken: GNU ld (Gentoo 2.29.1 p3) 2.29.1 > working: GNU ld (GNU Binutils for Ubuntu) 2.26.1
FWIW, this issue stems from this change: https://sourceware.org/bugzilla/show_bug.cgi?id=21458
The same issue caused problems in libavcodec as well, where we chose to work around the issue in this fashion: https://git.libav.org/?p=libav.git;a=commitdiff;h=9dde6ab06c48f9447cd16f39bee33569cddb7be4;hp=547db1eaecd597031165a2bf637acaaacde52788
Related debian bug report, with a different workaround: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=870622
(In libav, we chose the workaround since the .eqv one suggested in the debian bug report didn't really work well with assemblers for other platforms.)
// Martin
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