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PR18617 - Incorrect expression bytecode generated for narrowing conversions

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The existing code preserves 'from' bits, which is incorrect.  E.g.

 (gdb) maint agent-eval (char)255L
 Scope: 0x4008d6
 Reg mask: 00
   0  const16 255
   3  ext 64
   5  end

'ext 64' should be 'ext 8'; this bytecode evaluates to 255 instead of
the correct result of -1.  The fix is simple.  I ran the entire test
suite on x86-64 and there were no new test failures.

gdb/ChangeLog:
2015-07-08  Robert O'Callahan  <robert@ocallahan.org>

	PR exp/18617
	* ax-gdb.c (gen_conversion): Extend to 'to' bits, not 'from'.

gdb/testsuite/ChangeLog:
2015-07-08  Robert O'Callahan  <robert@ocallahan.org>

	PR exp/18617
	* gdb.trace/ax.exp: Add test.
This commit is contained in:
Robert O'Callahan
2015-07-08 10:53:36 +01:00
committed by Pedro Alves
parent e8643a4533
commit bcf5c1d96b
4 changed files with 13 additions and 1 deletions
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2
gdb/ax-gdb.c
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@@ -885,7 +885,7 @@ gen_conversion (struct agent_expr *ax, struct type *from, struct type *to)
/* If we're converting to a narrower type, then we need to clear out
the upper bits. */
if (TYPE_LENGTH (to) < TYPE_LENGTH (from))
gen_extend (ax, from);
gen_extend (ax, to);
/* If the two values have equal width, but different signednesses,
then we need to extend. */