[Bug 10601] New: Depreciated and no longer supported swpb instruction for ARM

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=10601

            Bug ID: 10601
           Summary: Depreciated and no longer supported swpb instruction
                    for ARM
           Product: uClibc
           Version: 0.9.33.2
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P5
         Component: Standard Compliance
          Assignee: unassigned at uclibc.org
          Reporter: jupiterict at gmail.com
                CC: uclibc-cvs at uclibc.org
  Target Milestone: ---

Hello, the ldso thumb_atomics.S file contains a greatly depreciated swpb
instruction that has not been supported by ARM processors since V7.  This means
that RPi units and other ARM based hardware will not work with it.
To correct this problem, I propose that swpb be replaced with ldrexb and strexb
which will read the register and memory address and byte-swap into the
specified register similarly to swpb.  It's extremely important to be certain
that this is implemented correctly as it may not be as simple as just changing
the command.

This should also make it thumb compatible so the .hidden swpb_thumb shouldn't
be required anymore.

Problems that may arise from this are the variations of ldrex and strex that
will work.  Also ensuring that having exclusive access won't affect future
accesses to the same register.

I'll leave it in your capable hands, but it's broke and getting more broken as
time goes on and newer processors come to light.

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