* dw2 frame unwinder - unaligned access
@ 2005-07-19 5:34 Vasanth
2005-07-19 6:04 ` Ian Lance Taylor
0 siblings, 1 reply; 2+ messages in thread
From: Vasanth @ 2005-07-19 5:34 UTC (permalink / raw)
To: gcc
Hi,
With reference to the following info in the EH handling newbie document,
http://gcc.gnu.org/ml/gcc/2002-07/msg00391.html
<snip>
The exception handing via dwarf2 debugging information requires
several things to work:
.........
-Unaligned accesses to read dwarf2 information
</snip>
What is the recommended way to do DW2 frame unwinding based exception
handling for targets that do not support unaligned accesses in
hardware? I did see the documentation about UNALIGNED_INT_ASM_OP, but
not sure if that is meant to generate a directive to the assembler to
produce an aligned int (the name indicates otherwise). Also, I see
UNALIGNED_INT_ASM_OP being used only in the VMS debugging source file.
So I am unsure how it relates to DW2 based frame unwinding.
thanks for any help,
regards,
Vasanth
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: dw2 frame unwinder - unaligned access
2005-07-19 5:34 dw2 frame unwinder - unaligned access Vasanth
@ 2005-07-19 6:04 ` Ian Lance Taylor
0 siblings, 0 replies; 2+ messages in thread
From: Ian Lance Taylor @ 2005-07-19 6:04 UTC (permalink / raw)
To: Vasanth; +Cc: gcc
Vasanth <geekvasanth@gmail.com> writes:
> What is the recommended way to do DW2 frame unwinding based exception
> handling for targets that do not support unaligned accesses in
> hardware? I did see the documentation about UNALIGNED_INT_ASM_OP, but
> not sure if that is meant to generate a directive to the assembler to
> produce an aligned int (the name indicates otherwise). Also, I see
> UNALIGNED_INT_ASM_OP being used only in the VMS debugging source file.
> So I am unsure how it relates to DW2 based frame unwinding.
UNALIGNED_INT_ASM_OP tells the assembler to not do any automatic
alignment before emitting the value. In current development sources
this is TARGET_ASM_UNALIGNED_SI_OP, and it is defined in a number of
config/*/*.c files.
It should not matter that your target does not support unaligned
access in hardware. The code in read_encoded_value_with_base in
unwind-pe.h should do the right thing, by using a packed union. On a
target which does not support unaligned access, it will use byte
reads.
If you really do want to insist that all accesses be aligned, it
should work to define ASM_PREFERRED_EH_DATA_FORMAT to be
DW_EH_PE_aligned.
Ian
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2005-07-19 6:04 ` Ian Lance Taylor
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