libgcc: Fix eh_frame fast path in find_fde_tail
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Commit Message
The eh_frame value is only used by linear_search_fdes, not the binary
search directly in find_fde_tail, so the bug is not immediately
apparent with most programs.
Fixes commit e724b0480bfa5ec04f39be8c7290330b495c59de ("libgcc:
Special-case BFD ld unwind table encodings in find_fde_tail").
[I'd appreciate suggestions how I could add a test for this. BFD ld
does not seem to allow ommitting the binary search table.]
libgcc/
PR libgcc/109712
* unwind-dw2-fde-dip.c (find_fde_tail): Correct fast path for
parsing eh_frame.
---
libgcc/unwind-dw2-fde-dip.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
base-commit: b327cbe8f4eefc91ee2bea49a1da7128adf30281
Comments
On Tue, Jun 6, 2023 at 11:53 AM Florian Weimer via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The eh_frame value is only used by linear_search_fdes, not the binary
> search directly in find_fde_tail, so the bug is not immediately
> apparent with most programs.
>
> Fixes commit e724b0480bfa5ec04f39be8c7290330b495c59de ("libgcc:
> Special-case BFD ld unwind table encodings in find_fde_tail").
OK.
> [I'd appreciate suggestions how I could add a test for this. BFD ld
> does not seem to allow ommitting the binary search table.]
>
> libgcc/
>
> PR libgcc/109712
> * unwind-dw2-fde-dip.c (find_fde_tail): Correct fast path for
> parsing eh_frame.
>
> ---
> libgcc/unwind-dw2-fde-dip.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libgcc/unwind-dw2-fde-dip.c b/libgcc/unwind-dw2-fde-dip.c
> index 6223f5f18a2..4e0b880513f 100644
> --- a/libgcc/unwind-dw2-fde-dip.c
> +++ b/libgcc/unwind-dw2-fde-dip.c
> @@ -403,8 +403,8 @@ find_fde_tail (_Unwind_Ptr pc,
> BFD ld generates. */
> signed value __attribute__ ((mode (SI)));
> memcpy (&value, p, sizeof (value));
> + eh_frame = p + value;
> p += sizeof (value);
> - dbase = value; /* No adjustment because pcrel has base 0. */
> }
> else
> p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc,
>
> base-commit: b327cbe8f4eefc91ee2bea49a1da7128adf30281
>
@@ -403,8 +403,8 @@ find_fde_tail (_Unwind_Ptr pc,
BFD ld generates. */
signed value __attribute__ ((mode (SI)));
memcpy (&value, p, sizeof (value));
+ eh_frame = p + value;
p += sizeof (value);
- dbase = value; /* No adjustment because pcrel has base 0. */
}
else
p = read_encoded_value_with_base (hdr->eh_frame_ptr_enc,