Re: [PATCH v4 5/5] powerpc/vdso: Wire up getrandom() vDSO implementation on PPC64

Jason A. Donenfeld
2024-09-02T14:00:32Z

On Mon, Sep 02, 2024 at 03:12:47PM +0200, Christophe Leroy wrote:
>
>
> Le 02/09/2024 à 14:41, Jason A. Donenfeld a écrit :
> > On Mon, Sep 02, 2024 at 02:04:42PM +0200, Christophe Leroy wrote:
> >> SYM_FUNC_START(__arch_chacha20_blocks_nostack)
> >> #ifdef __powerpc64__
> >> - blr
> >> + std r5, -216(r1)
> >> +
> >> + std r14, -144(r1)
> >> + std r15, -136(r1)
> >> + std r16, -128(r1)
> >> + std r17, -120(r1)
> >> + std r18, -112(r1)
> >> + std r19, -104(r1)
> >> + std r20, -96(r1)
> >> + std r21, -88(r1)
> >> + std r22, -80(r1)
> >> + std r23, -72(r1)
> >> + std r24, -64(r1)
> >> + std r25, -56(r1)
> >> + std r26, -48(r1)
> >> + std r27, -40(r1)
> >> + std r28, -32(r1)
> >> + std r29, -24(r1)
> >> + std r30, -16(r1)
> >> + std r31, -8(r1)
> >> #else
> >> stwu r1, -96(r1)
> >> stw r5, 20(r1)
> >> +#ifdef __BIG_ENDIAN__
> >> stmw r14, 24(r1)
> >> +#else
> >> + stw r14, 24(r1)
> >> + stw r15, 28(r1)
> >> + stw r16, 32(r1)
> >> + stw r17, 36(r1)
> >> + stw r18, 40(r1)
> >> + stw r19, 44(r1)
> >> + stw r20, 48(r1)
> >> + stw r21, 52(r1)
> >> + stw r22, 56(r1)
> >> + stw r23, 60(r1)
> >> + stw r24, 64(r1)
> >> + stw r25, 68(r1)
> >> + stw r26, 72(r1)
> >> + stw r27, 76(r1)
> >> + stw r28, 80(r1)
> >> + stw r29, 84(r1)
> >> + stw r30, 88(r1)
> >> + stw r31, 92(r1)
> >> +#endif
> >> +#endif
> >
> > This confuses me. Why are you adding code to the !__powerpc64__ branch
> > in this commit? (Also, why does stmw not work on LE?)
>
> That's for the VDSO32 ie running 32 bits binaries on a 64 bits kernel.
>
> "Programming Environments Manual for 32-Bit Implementations of the
> PowerPC™ Architecture" say: In some implementations operating with
> little-endian byte order, execution of an lmw or stmw instruction
> causes the system alignment error handler to be invoked
>
> And GCC doesn't like it either:
>
> tools/arch/powerpc/vdso/vgetrandom-chacha.S:84: Error: `stmw' invalid
> when little-endian

Does it make sense to do all the 32-bit stuff in the PPC32 commit (and
then you can introduce the selftests there without the error you
mentioned), and then add the 64-bit stuff in this commit?