libgcc: Align __EH_FRAME_BEGIN__ to pointer size
Commit Message
Aligne __EH_FRAME_BEGIN__ to pointer size since gcc/unwind-dw2-fde.h has
/* The first few fields of a CIE. The CIE_id field is 0 for a CIE,
to distinguish it from a valid FDE. FDEs are aligned to an addressing
unit boundary, but the fields within are unaligned. */
struct dwarf_cie
{
uword length;
sword CIE_id;
ubyte version;
unsigned char augmentation[];
} __attribute__ ((packed, aligned (__alignof__ (void *))));
/* The first few fields of an FDE. */
struct dwarf_fde
{
uword length;
sword CIE_delta;
unsigned char pc_begin[];
} __attribute__ ((packed, aligned (__alignof__ (void *))));
which indicates that CIE/FDE should be aligned at the pointer size.
PR libgcc/27576
* crtstuff.c (__EH_FRAME_BEGIN__): Aligned to pointer size.
---
libgcc/crtstuff.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
Comments
On 1/18/2022 10:09 AM, H.J. Lu via Gcc-patches wrote:
> Aligne __EH_FRAME_BEGIN__ to pointer size since gcc/unwind-dw2-fde.h has
>
> /* The first few fields of a CIE. The CIE_id field is 0 for a CIE,
> to distinguish it from a valid FDE. FDEs are aligned to an addressing
> unit boundary, but the fields within are unaligned. */
> struct dwarf_cie
> {
> uword length;
> sword CIE_id;
> ubyte version;
> unsigned char augmentation[];
> } __attribute__ ((packed, aligned (__alignof__ (void *))));
>
> /* The first few fields of an FDE. */
> struct dwarf_fde
> {
> uword length;
> sword CIE_delta;
> unsigned char pc_begin[];
> } __attribute__ ((packed, aligned (__alignof__ (void *))));
>
> which indicates that CIE/FDE should be aligned at the pointer size.
>
> PR libgcc/27576
> * crtstuff.c (__EH_FRAME_BEGIN__): Aligned to pointer size.
OK. Though it's unclear how important this is in practice.
jeff
@@ -261,7 +261,8 @@ STATIC func_ptr __DTOR_LIST__[1]
/* Stick a label at the beginning of the frame unwind info so we can register
and deregister it with the exception handling library code. */
STATIC EH_FRAME_SECTION_CONST char __EH_FRAME_BEGIN__[]
- __attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__), aligned(4)))
+ __attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__),
+ aligned(__alignof__ (void *))))
= { };
#endif /* USE_EH_FRAME_REGISTRY */