Re: Relative expressions and ASSERT

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Dec 16, 2010 at 3:02 AM, Alan Modra <amodra@gmail.com> wrote:
> On Wed, Dec 15, 2010 at 08:25:17PM -0800, H.J. Lu wrote:
>> On Thu, Aug 12, 2010 at 4:38 PM, Alan Modra <amodra@gmail.com> wrote:
>> > On Thu, Aug 12, 2010 at 08:47:25AM -0700, H.J. Lu wrote:
>> >> You can try the new linker on Linux kernel.
>> >
>> > An x86 2.6.35 kernel built without any differences.
>> >
>>
>> It caused:
>>
>> http://sourceware.org/bugzilla/show_bug.cgi?id=12327
>
> I was expecting this to cause some trouble. ?You can't avoid breaking
> some linker scripts when you change the linker expression evaluation
> rules (really, give it some rules rather than the adhoc mess that was
> there before). ?I wonder if I should have gone a little further, and
> removed the special case for expressions outside of an output section
> definition. ?It's what I really wanted to do, but ran into a number of
> testsuite failures in our own testsuite when I originally tried that.
> Now that we differentiate between plain numbers and absolute symbols,
> only one testcase needs adjusting.
>
> So, if I commit this, scripts like the testcase below will need some
> asjustment. ?On the other hand, sym1 = sym2 assignments should work
> like they used to outside of an output section statement, fixing the
> kernel problem and
> frv-linux FAIL: FRV uClinux PIC relocs to weak undefined symbols, pie linking
> frv-linux FAIL: FRV uClinux PIC relocs to weak undefined symbols, shared linking
>
> How to people feel about this for 2.21.1?
>
> ld/
> ? ? ? ?* ldexp.c (exp_fold_tree_1): Don't make subexpressions absolute
> ? ? ? ?when outside of an output section statement.
> ? ? ? ?* ld.texinfo (Expression Section): Update description.
> ld/testsuite/
> ? ? ? ?* ld-scripts/align.t: Make ADDR absolute.
>
> Index: ld/ldexp.c
> ===================================================================
> RCS file: /cvs/src/src/ld/ldexp.c,v
> retrieving revision 1.87
> diff -u -p -r1.87 ldexp.c
> --- ld/ldexp.c ?1 Oct 2010 08:15:41 -0000 ? ? ? 1.87
> +++ ld/ldexp.c ?16 Dec 2010 08:52:09 -0000
> @@ -858,12 +858,6 @@ exp_fold_tree_1 (etree_type *tree)
> ? ? ? memset (&expld.result, 0, sizeof (expld.result));
> ? ? ? break;
> ? ? }
> -
> - ?/* Any value not inside an output section statement is an
> - ? ? absolute value. ?*/
> - ?if (expld.result.valid_p
> - ? ? ?&& expld.section == bfd_abs_section_ptr)
> - ? ?make_abs ();
> ?}
>
> ?void
> Index: ld/ld.texinfo
> ===================================================================
> RCS file: /cvs/src/src/ld/ld.texinfo,v
> retrieving revision 1.268
> diff -u -p -r1.268 ld.texinfo
> --- ld/ld.texinfo ? ? ? 15 Dec 2010 14:56:37 -0000 ? ? ?1.268
> +++ ld/ld.texinfo ? ? ? 16 Dec 2010 08:52:59 -0000
> @@ -5505,15 +5505,13 @@ address, such as @code{ADDR}, @code{LOAD
> ?functions that return a non-address value, such as @code{LENGTH}.
>
> ?When the linker evaluates an expression, the result depends on where
> -the expression is located in a linker script. ?Expressions appearing
> -outside an output section definitions are evaluated with all terms
> -first being converted to absolute addresses before applying operators,
> -and evaluate to an absolute address result. ?Expressions appearing
> -inside an output section definition are evaluated with more complex
> -rules, but the aim is to treat terms as relative addresses and produce
> -a relative address result. ?In particular, an assignment of a number
> -to a symbol results in a symbol relative to the output section with an
> -offset given by the number. ?So, in the following simple example,
> +the expression is located in a linker script. ?Outside of an output
> +section definition, a result that is a number is treated as an
> +absolute address. ?Inside an output section definition, a result that
> +is a number is treated as a relative address. ?In particular, an
> +assignment of a number to a symbol results in a symbol relative to the
> +output section with an offset given by the number. ?So, in the
> +following simple example,
>
> ?@smallexample
> ?@group
> @@ -5537,9 +5535,8 @@ address 0x100 in the first two assignmen
> ?@code{__data_start} are set to 0x10 relative to the @code{.data}
> ?section in the second two assignments.
>
> -For expressions appearing inside an output section definition
> -involving numbers, relative addresses and absolute addresses, ld
> -follows these rules to evaluate terms:
> +For expressions involving numbers, relative addresses and absolute
> +addresses, ld follows these rules to evaluate terms:
>
> ?@itemize @bullet
> ?@item
> Index: ld/testsuite/ld-scripts/align.t
> ===================================================================
> RCS file: /cvs/src/src/ld/testsuite/ld-scripts/align.t,v
> retrieving revision 1.1
> diff -u -p -r1.1 align.t
> --- ld/testsuite/ld-scripts/align.t ? ? 20 Feb 2004 15:31:10 -0000 ? ? ?1.1
> +++ ld/testsuite/ld-scripts/align.t ? ? 16 Dec 2010 08:52:10 -0000
> @@ -4,5 +4,5 @@ SECTIONS
> ? .data ALIGN(0x40) : AT (ALIGN (LOADADDR (.text) + SIZEOF (.text), 0x80))
> ? ? {}
> ? ASSERT (LOADADDR(.data) == 0x80, "dyadic ALIGN broken")
> - ?ASSERT (ADDR(.data) == 0x40, "monadic ALIGN broken")
> + ?ASSERT (ABSOLUTE(ADDR(.data)) == 0x40, "monadic ALIGN broken")
> ?}
>

Did it work before your change on Aug 19, 2010?

-- 
H.J.