[Bug 205663] clang++ 3.7.1 gets Bus Errors during compilation on arm that has SCTLR bit[1]==1 (alignment required)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=205663

--- Comment #3 from Mark Millard <markmi at dsl-only.net> ---
Below is what llvm-org's James Molloy reports about needing
-mno-unaligned-access when building clang and clang++ for use in a SCTLR
bit[1]==1 context:

From: bugzilla-daemon at llvm.org
Subject: [Bug 25958] FreeBSD 11.0-CURRENT clang++ 3.7.1 gets Bus Errors during
compilation on arm that has SCTLR bit[1]==1 (alignment required)
Date: December 28, 2015 at 1:28:28 PM PST
To: <markmi at dsl-only.net>

James Molloy changed bug 25958 
What    Removed Added
CC              james.molloy at arm.com

Comment # 2 on bug 25958 from James Molloy
Hi Mark,

Thanks for raising this. Before checking the specifics of what you found - did
you compile Clang with -mno-unaligned-access? We will by default compile
assuming SCTLR.A is 0. -mno-unaligned-access switches this assumption off and
enables strict alignment mode.

Cheers,

James


More notes:

I've answered with the example compilation command for the specific clang
source file, extracted from a script log of my build: I had used
-mno-unaligned-access.

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