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ld expression section

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Changes the result of ld expressions that were previously plain
numbers to be an absolute address, in the same circumstances where
numbers are treated as absolute addresses.

	* ld.texinfo (Expression Section): Update result of arithmetic
	expressions.
	* ldexp.c (arith_result_section): New function.
	(fold_binary): Use it.
This commit is contained in:
Alan Modra 2016-10-04 10:43:50 +10:30
parent 9ad39107ca
commit 94b41882b0
3 changed files with 39 additions and 22 deletions
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7
ld/ChangeLog
View File

@ -1,3 +1,10 @@
2016-10-04 Alan Modra <amodra@gmail.com>
* ld.texinfo (Expression Section): Update result of arithmetic
expressions.
* ldexp.c (arith_result_section): New function.
(fold_binary): Use it.
2016-10-04 Alan Modra <amodra@gmail.com>
* ldexp.c (exp_value_fold): New function.

4
ld/ld.texinfo
View File

@ -6032,7 +6032,9 @@ The result of comparisons, @samp{&&} and @samp{||} is also a number.
@item
The result of other binary arithmetic and logical operations on two
relative addresses in the same section or two absolute addresses
(after above conversions) is also a number.
(after above conversions) is also a number when
@code{LD_FEATURE ("SANE_EXPR")} or inside an output section definition
but an absolute address otherwise.
@item
The result of other operations on relative addresses or one
relative address and a number, is a relative address in the same

50
ld/ldexp.c
View File

@ -417,6 +417,32 @@ fold_unary (etree_type *tree)
}
}
/* Arithmetic operators, bitwise AND, bitwise OR and XOR keep the
section of one of their operands only when the other operand is a
plain number. Losing the section when operating on two symbols,
ie. a result of a plain number, is required for subtraction and
XOR. It's justifiable for the other operations on the grounds that
adding, multiplying etc. two section relative values does not
really make sense unless they are just treated as numbers.
The same argument could be made for many expressions involving one
symbol and a number. For example, "1 << x" and "100 / x" probably
should not be given the section of x. The trouble is that if we
fuss about such things the rules become complex and it is onerous
to document ld expression evaluation. */
static void
arith_result_section (const etree_value_type *lhs)
{
if (expld.result.section == lhs->section)
{
if (expld.section == bfd_abs_section_ptr
&& !config.sane_expr)
/* Duplicate the insanity in exp_fold_tree_1 case etree_value. */
expld.result.section = bfd_abs_section_ptr;
else
expld.result.section = NULL;
}
}
static void
fold_binary (etree_type *tree)
{
@ -483,26 +509,10 @@ fold_binary (etree_type *tree)
switch (tree->type.node_code)
{
/* Arithmetic operators, bitwise AND, bitwise OR and XOR
keep the section of one of their operands only when the
other operand is a plain number. Losing the section when
operating on two symbols, ie. a result of a plain number,
is required for subtraction and XOR. It's justifiable
for the other operations on the grounds that adding,
multiplying etc. two section relative values does not
really make sense unless they are just treated as
numbers.
The same argument could be made for many expressions
involving one symbol and a number. For example,
"1 << x" and "100 / x" probably should not be given the
section of x. The trouble is that if we fuss about such
things the rules become complex and it is onerous to
document ld expression evaluation. */
#define BOP(x, y) \
case x: \
expld.result.value = lhs.value y expld.result.value; \
if (expld.result.section == lhs.section) \
expld.result.section = NULL; \
arith_result_section (&lhs); \
break;
/* Comparison operators, logical AND, and logical OR always
@ -536,8 +546,7 @@ fold_binary (etree_type *tree)
% (bfd_signed_vma) expld.result.value);
else if (expld.phase != lang_mark_phase_enum)
einfo (_("%F%S %% by zero\n"), tree->binary.rhs);
if (expld.result.section == lhs.section)
expld.result.section = NULL;
arith_result_section (&lhs);
break;
case '/':
@ -546,8 +555,7 @@ fold_binary (etree_type *tree)
/ (bfd_signed_vma) expld.result.value);
else if (expld.phase != lang_mark_phase_enum)
einfo (_("%F%S / by zero\n"), tree->binary.rhs);
if (expld.result.section == lhs.section)
expld.result.section = NULL;
arith_result_section (&lhs);
break;
case MAX_K: