Wilco Dijkstra <wilco.dijks...@arm.com> writes:
> A recent change only initializes the regs.how[] during Dwarf unwinding
> which resulted in an uninitialized offset used in return address signing
> and random failures during unwinding. The fix is to use REG_SAVED_OFFSET
> as the state where the return address signing bit is valid, and if the
> state is REG_UNSAVED, initialize it to 0.
>
> Passes bootstrap & regress, OK for commit?
>
> libgcc/
> PR target/107678
> * unwind-dw2.c (execute_cfa_program): Initialize offset of
> DWARF_REGNUM_AARCH64_RA_STATE if in REG_UNSAVED state.
> * config/aarch64/aarch64-unwind.h (aarch64_frob_update_contex):
> Check state is REG_SAVED_OFFSET before using offset for RA state.
>
> ---
>
> diff --git a/libgcc/config/aarch64/aarch64-unwind.h
> b/libgcc/config/aarch64/aarch64-unwind.h
> index
> 26db9cbd9e5c526e0c410a4fc6be2bedb7d261cf..597133b3d708a50a366c8bfeff57475f5522b3f6
> 100644
> --- a/libgcc/config/aarch64/aarch64-unwind.h
> +++ b/libgcc/config/aarch64/aarch64-unwind.h
> @@ -71,21 +71,15 @@ aarch64_demangle_return_addr (struct _Unwind_Context
> *context,
> }
>
> /* Do AArch64 private initialization on CONTEXT based on frame info FS. Mark
> - CONTEXT as return address signed if bit 0 of
> DWARF_REGNUM_AARCH64_RA_STATE is
> - set. */
> + CONTEXT as having a signed return address if DWARF_REGNUM_AARCH64_RA_STATE
> + is initialized (REG_SAVED_OFFSET state) and the offset has bit 0 set. */
>
> static inline void
> aarch64_frob_update_context (struct _Unwind_Context *context,
> _Unwind_FrameState *fs)
> {
> - const int reg = DWARF_REGNUM_AARCH64_RA_STATE;
> - int ra_signed;
> - if (fs->regs.how[reg] == REG_UNSAVED)
> - ra_signed = fs->regs.reg[reg].loc.offset & 0x1;
> - else
> - ra_signed = _Unwind_GetGR (context, reg) & 0x1;
> - if (ra_signed)
> - /* The flag is used for re-authenticating EH handler's address. */
> + if (fs->regs.how[DWARF_REGNUM_AARCH64_RA_STATE] == REG_SAVED_OFFSET
> + && (fs->regs.reg[DWARF_REGNUM_AARCH64_RA_STATE].loc.offset & 1) != 0)
> context->flags |= RA_SIGNED_BIT;
> else
> context->flags &= ~RA_SIGNED_BIT;
Hmm, but the point of the original patch was to support code generators
that emit DW_CFA_val_expression instead of DW_CFA_AARCH64_negate_ra_state.
Doesn't this patch undo that?
Also, if I understood correctly, the reason we use REG_UNSAVED is to
ensure that state from one frame isn't carried across to a parent frame,
in cases where the parent frame lacks any signing. That is, each frame
should start out with a zero bit even if a child frame is unwound while
it has a set bit.
Thanks,
Richard
> diff --git a/libgcc/unwind-dw2.c b/libgcc/unwind-dw2.c
> index
> eaceace20298b9b13344aff9d1fe9ee5f9c7bd73..87f2ae065b67982ce48f74e45523d9c754a7661c
> 100644
> --- a/libgcc/unwind-dw2.c
> +++ b/libgcc/unwind-dw2.c
> @@ -1203,11 +1203,16 @@ execute_cfa_program (const unsigned char *insn_ptr,
>
> case DW_CFA_GNU_window_save:
> #if defined (__aarch64__) && !defined (__ILP32__)
> - /* This CFA is multiplexed with Sparc. On AArch64 it's used to toggle
> - return address signing status. */
> - reg = DWARF_REGNUM_AARCH64_RA_STATE;
> - gcc_assert (fs->regs.how[reg] == REG_UNSAVED);
> - fs->regs.reg[reg].loc.offset ^= 1;
> + /* This CFA is multiplexed with Sparc. On AArch64 it's used to toggle
> + the return address signing status. It is initialized at the first
> + use and the state is stored in bit 0 of the offset. */
> + reg = DWARF_REGNUM_AARCH64_RA_STATE;
> + if (fs->regs.how[reg] == REG_UNSAVED)
> + {
> + fs->regs.how[reg] = REG_SAVED_OFFSET;
> + fs->regs.reg[reg].loc.offset = 0;
> + }
> + fs->regs.reg[reg].loc.offset ^= 1;
> #else
> /* ??? Hardcoded for SPARC register window configuration. */
> if (__LIBGCC_DWARF_FRAME_REGISTERS__ >= 32)
