From llvm: Fwd: [Bug 26519] Clang 3.8.0's "Target: powerpc-unknown-freebsd11.0" code generation is violating the SVR4 ABI (SEGV can result) [fixed in llvm -r280705]

[Mark Millard]

On 2016-Sep-10, at 10:18 AM, Dimitry Andric <dim at FreeBSD.org> wrote:

> On 06 Sep 2016, at 15:04, Mark Millard <markmi at dsl-only.net> wrote:
>> 
>> llvm's bugzilla reports that the stack-handling SVR4 ABI violation for TARGET_ARCH=powerpc has been fixed r280705 (likely on trunk)!
> 
> I merged the upstream fix to projects/clang390-import:
> 
> https://svnweb.freebsd.org/changeset/base/305686
> 
> -Dimitry

Looking at things for this again I've submitted a question to https://llvm.org/bugs/show_bug.cgi?id=26519 asking if the post-amble code's side if things was also adjusted (instead of just the pre-amble/"claim" code side of things).

[I'm not clang/llvm literate so I may have missed interpreted something when I looked.]

My original submittal also noted the stack pointer adjustment-timing problem existed on the post-amble side in 3.8.0's code generation (when removing the frame from the stack):

> 0x1801b8c <Buf_AddBytes+104>:	lwz     r30,24(r31)
> 0x1801b90 <Buf_AddBytes+108>:	lwz     r29,20(r31)
> 0x1801b94 <Buf_AddBytes+112>:	lwz     r28,16(r31)
> 0x1801b98 <Buf_AddBytes+116>:	lwz     r27,12(r31)
> 0x1801b9c <Buf_AddBytes+120>:	lwz     r26,8(r31)
> 0x1801ba0 <Buf_AddBytes+124>:	addi    r1,r1,32   # Stack pointer adjusted first
> 0x1801ba4 <Buf_AddBytes+128>:	lwz     r0,4(r1)
> 0x1801ba8 <Buf_AddBytes+132>:	lwz     r31,-4(r1) # Then Frame Pointer load happens
>                                                    # "outside" the new stack range.
> 0x1801bac <Buf_AddBytes+136>:	mtlr    r0
> 0x1801bb0 <Buf_AddBytes+140>:	blr

If such code can still be generated there would still be a time frame needing a red-zone to protect stack the contents from signals.

Hopefully I'm just wrong and this was fixed too.



===
Mark Millard
markmi at dsl-only.net