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[PATCH, ARM] Fix bl->blx conversion for object-local targets

Julian Brown julian@codesourcery.com
Tue Nov 6 19:05:00 GMT 2012 
Hi,

Gas has logic which is supposed to turn Thumb BL instructions into BLX
instructions when targeting local ARM symbols (and similarly for ARM BL
instructions targeting local Thumb symbols). Unfortunately this is
flawed at present, and can lead to incorrectly-encoded BLX instructions.

The attached patch fixes this. The condition inside the #ifdef is
moved lower down the function (otherwise the rounding-up of "value" to a
word boundary never triggers after BL->BLX conversions), and the code
which actually does the rounding is altered to match the comment -- I'm
pretty sure in this case the comment was correct, but the code was only
rounding up to a half-word boundary rather than a word boundary as
stated.

This bug manifested for me as a failure in GCC testing
(g++.dg/ipa/pr46984.C in Thumb-1 mode), but only because that test
happens to insert ARM-mode code (for a MI thunk) into Thumb output.

I've added a new test, which passes with the patch, and fails without.
No other regressions (gas tests), cross to ARM Linux. OK to apply?

(Incidentally, an orthogonal problem might be that the ARM1176 erratum
workaround described at:

  http://sourceware.org/ml/binutils/2011-07/msg00235.html

is not taken into account when performing this kind of conversion. I'm
not planning on tackling that issue though.)

Thanks,

Julian

ChangeLog

    gas/
    * config/tc-arm.c (md_apply_fix): Fix conversion of BL to BLX for
    local targets in Thumb mode.

    gas/testsuite/
    * gas/arm/bl-local-2.s: New test.
    * gas/arm/bl-local-2.d: New.
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