Date: Tue, 30 Aug 2016 18:17:32 -0700 From: Mark Millard <markmi@dsl-only.net> To: FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: From llvm: Fwd: [Bug 26856] clang 3.8.0/powerpc/powerpc64's _Unwind_RaiseException code generation has messed up r31 (frame pointer) save/restore code (SEGV's can result) [another issue reported fixed, via llvm r280188] Message-ID: <13C54407-8758-41E8-BBDB-4C3574D05C61@dsl-only.net> References: <bug-26856-7604-4taR3C2xLm@http.llvm.org/bugs/>
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The below notice from Hal Finkel [via llvm's bugzilla] indicates that at =
least part of llvm bug 26856 for powerpc64's is expected to have been =
fixed by r280188 (likely on trunk?).
26856 was one of my reports that had independent confirmation back when =
I submitted it. Some of the quote below is from the exchange about the =
problems from back then.
=3D=3D=3D
Mark Millard
markmi at dsl-only.net
Begin forwarded message:
From: bugzilla-daemon at llvm.org
Subject: [Bug 26856] clang 3.8.0/powerpc/powerpc64's =
_Unwind_RaiseException code generation has messed up r31 (frame pointer) =
save/restore code (SEGV's can result)
Date: August 30, 2016 at 5:54:45 PM PDT
To: <markmi at dsl-only.net>
Comment # 11 on bug 26856 from Hal Finkel
(In reply to comment #6
)
...
>=20
> 2) In some scenarios, registers may be spilled/restored twice to the =
stack.=20
> This happens because while most of the spilling happens in
> PPCFrameLowering::spillCalleeSavedRegisters, a few selected registers =
are
> also spilled in PPCFrameLowering::emitPrologue. Those registers are =
the
> frame pointer, base pointer, PIC base pointer, link register, and =
condition
> code register. For the latter two, code ensures that they can never =
be
> spilled in both places (for CR, there is extra code in
> spillCalleeSavedRegisters; for LR, the register is removed from =
SavedRegs in
> determineCalleeSaves).
>=20
> However, for FP, BP, and PBP, nothing ensures the registers are not =
spilled
> twice. It is probably *rare* for this to happen, because the register
> allocator will not use those registers within the function if they're =
needed
> for their special purpose, but it can happen in rare cases. This =
includes
> the case of a system unwinder routine that uses __builtin_unwind_init, =
but
> could also include other routines that clobber one of those registers, =
e.g.
> the following case:
>=20
> void func (void);
>=20
> void test (void)
> {
> func ();
> asm ("nop" : : : "31");
> }
r280188 should address the spilling-twice problem.
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