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[PATCH] MIPS/GAS: Complain about missed fixups
- From: "Maciej W. Rozycki" <macro at codesourcery dot com>
- To: <binutils at sourceware dot org>
- Cc: Richard Sandiford <rdsandiford at googlemail dot com>
- Date: Fri, 21 Sep 2012 18:30:00 +0100
- Subject: [PATCH] MIPS/GAS: Complain about missed fixups
This is really the same case as was with HI16 relocations before their
handling was corrected as a part of this issue, except that it applies to
several other relocations. The case is as follows: an expression is not
fully resolved at append_insn time, a fixup is created. Later on the
expression turns out constant (e.g. forward symbol references are
satisfied) and by the time md_apply_fix is called it has been fully
evaluated. However md_apply_fix does nothing about it, any outstanding
relocation decays to nil and the relocatable field remains initialised to
zero as final output is produced.
One such case is code like this:
li $2, %higher(1f - 0b)
Of course code like above makes little sense, the distance between 0 and 1
would have to be over 2GB for the relocation to come out as non-zero. So
there is little point in bending backwards and adding extra code to apply
this relocation in md_apply_fix. The same stands for %highest for
example, however to complement the %hi/%lo fix I think this have to be
caught just in case someone does something weird (at which point we may
decide to implement the missing bit after all).
Then I am not even sure what kind of calculation is supposed to be made
for cases like:
li $2, %got(1f - 0b)
and several other ones. However I don't think such an expression should
be silently ignored, it's almost certainly a sign of a user error, so I
think proper diagnostics needs to be added to warn about the situation.
As this can be triggered with user code I have decided the diagnostics
should be a proper error message and not an internal failure (which is BTW
the case for the same relocations resolved straight away in append_insn,
e.g. li $2, %got(0); fixed with another patch). Regression-tested for
MIPS targets with no problems; I have put it through a GCC/glibc build
just to be sure it does not uncover a problem there.
OK to apply?
2012-09-21 Maciej W. Rozycki <firstname.lastname@example.org>
* config/tc-mips.c (md_apply_fix): Complain about missed fixups.
--- binutils-fsf-trunk-quilt.orig/gas/config/tc-mips.c 2012-09-17 22:18:33.000000000 +0100
+++ binutils-fsf-trunk-quilt/gas/config/tc-mips.c 2012-09-17 22:19:20.450746744 +0100
@@ -15521,6 +15521,9 @@ md_apply_fix (fixS *fixP, valueT *valP,
+ if (fixP->fx_done)
+ as_bad_where (fixP->fx_file, fixP->fx_line,
+ _("Unsupported constant in relocation"));
/* Nothing needed to do. The value comes from the reloc entry. */