"V, Aneesh" <ane...@ti.com> wrote:
> I agree that not marking the assembly functions ' %function' is a problem
> in the code, so it's not a critical bug. But I would've been happier if
> the linker refused to link it rather than branching with the wrong
> instruction. Isn't that a problem?
Well, if the target symbol of a branch is not marked as %function,
the linker has no way of knowing whether that target is ARM or Thumb,
so it cannot specifically error out if (and only if) the instruction
is wrong.
The linker *could* in theory give an error *unconditionally* whenever
it detects a branch to a non-%function symbol. The reason this is not
done is probably for backwards compatibility with old hand-written code,
say from an ARM-only era: branches to non-function symbols used to be
allowed, and in fact work fine if all code is ARM-only. Adding an error
would break such old code.
> Problem No:2
> *************
> Linaro GCC 2012.01 is giving a new problem w.r.to Thumb build
> that is not existing in Sourcery G++ Lite 2010q1-202. However, I
> couldn't reproduce this problem with a small program like above. So,
> let me give you reference to the original u-boot code that shows the
> problem and steps to reproduce it.
[snip]
> Please note that the .rodata symbols have odd addresses. These arrays
> actually need to be aligned at least to half-word boundary. In fact, in
> the image I verified that they are put at even addresses. So, the
> symbols have been kept as real address +1.
This seems strange. How did you verify "that they are put at even
addresses"?
I can reproduce the odd addresses of .rodata symbols. However, this
occurs simply because the linker put *no* alignment requirement whatsoever
on those sections:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk
Inf Al
[snip]
[11] .rodata.wkup_padc PROGBITS 00000000 000100 000004 00 A 0
0 1
[12] .rodata.wkup_padc PROGBITS 00000000 000104 000048 00 A 0
0 1
[13] .rodata.wkup_padc PROGBITS 00000000 00014c 00000c 00 A 0
0 1
[14] .rodata.wkup_padc PROGBITS 00000000 000158 000004 00 A 0
0 1
Note the "Al" column values of 1. In the final executable, those sections
happen to end up immediately following a .rodata.str string section with
odd
lenght, and since they don't have any alignment requirement, they start out
at an odd address.
The reason for the lack of alignment requirement is actually in the source:
const struct pad_conf_entry core_padconf_array_essential[] = {
where
struct pad_conf_entry {
u16 offset;
u16 val;
} __attribute__ ((packed));
The "packed" attribute specifies that all struct elements ought to be
considered to have alignment requirement 1 instead of their default
alignment. Thus the whole struct ends up having alignment requirement 1;
and since the section contains only a single variable of such struct
type, this is then also the alignment requirement of the section.
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz | Geschäftsführung: Dirk
Wittkopp
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
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