https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91306
Bug ID: 91306
Summary: [MSP430] libgcc/crtstuff.c: Alignment of frame_dummy
.init_array entry is too big
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgcc
Assignee: unassigned at gcc dot gnu.org
Reporter: jozefl.gcc at gmail dot com
Target Milestone: ---
In libgcc/crtstuff.c, an alignment of "sizeof (void *)" (i.e. pointer size)
is enforced for the frame_dummy() init_array entry. For msp430-elf in the
large memory model (-mlarge), pointer size is 4 bytes, but the expected
alignment of a pointer is 2 bytes.
So when .init_array is constructed, there could be padding added at the
beginning or between entries, since the structure itself is only aligned to
2 bytes but this entry is aligned to 4 bytes.
The padding causes incorrect execution since the code to run through
.init_array does not expect any gaps between entries since pointers only need
to be 2 byte aligned.
I see this alignment of "sizeof (void *)" was added to fix a mips64 bootstrap
failure in r182066 (https://gcc.gnu.org/ml/gcc-patches/2011-12/msg00393.html),
but this alignment isn't appropriate for msp430.
In crtstuff.c, the type of the init_array entry for frame_dummy is specified
to be "void *", so why must the alignment also be specified?
I don't have access to a mips platform, but shouldn't the entry have the
correct alignment for the type?
Was the addition of the aligned attribute in the 2011 commit a workaround for a
GCC bug? Can it be removed now?
For the following code, GCC generates the the correct alignment without using
the "aligned" attribute on x86, x86_64 and msp430-elf/-mlarge.
static void * entry[]
__attribute__ ((used, section(".init_array"))) = { foo };
x86_64-pc-linux-gnu -m32:
> .section .init_array,"aw"
> .align 4
> .type entry, @object
> .size entry, 4
>entry:
> .long foo
x86_64-pc-linux-gnu -m64:
> .section .init_array,"aw"
> .align 8
> .type entry, @object
> .size entry, 8
>entry:
> .quad foo
msp430-elf -mlarge:
> .section .init_array,"aw"
> .balign 2
> .type entry, @object
> .size entry, 4
>entry:
> .long foo
