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Date: Mon, 26 Sep 2022 13:08:43 +0200 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Geert Uytterhoeven <geert@...ux-m68k.org> Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org, Laurent Vivier <laurent@...ier.eu> Subject: Re: [PATCH v3 3/3] m68k: rework BI_VIRT_RNG_SEED as BI_RNG_SEED Hi Geert, On Mon, Sep 26, 2022 at 12:27:13PM +0200, Geert Uytterhoeven wrote: > The approach LGTM, but given my doubts on [PATCH v3 2/3], I think this > patch should be moved up, to not depend on [2/3]. I'll do that. But also, I'm not sure I yet agree with you about 2/3, so we should keep discussing that. (I'll still move it to 3/3 though.) > > -#define BI_VIRT_RNG_SEED 0x8006 > > +/* No longer used -- replaced with BI_RNG_SEED -- but don't reuse this index: > > + * #define BI_VIRT_RNG_SEED 0x8006 */ > > Please drop the space before TAB. Ack. > > > --- a/arch/m68k/include/uapi/asm/bootinfo.h > > +++ b/arch/m68k/include/uapi/asm/bootinfo.h > > @@ -64,7 +64,13 @@ struct mem_info { > > /* (struct mem_info) */ > > #define BI_COMMAND_LINE 0x0007 /* kernel command line parameters */ > > /* (string) */ > > - > > +/* > > + * A random seed used to initialize the RNG. Record format: > > + * > > + * - length [ 2 bytes, 16-bit big endian ] > > + * - seed data [ `length` bytes, padded to preserve 2-byte alignment ] > > While experimenting, I noticed this must actually be a 4-byte alignment, > as data[] is an integral multiple of __be32 words: > > struct bi_record { > __be16 tag; /* tag ID */ > __be16 size; /* size of record (in bytes) */ > __be32 data[]; /* data */ > }; > > m68kboot[1] and kexec-boot[2] do implement the correct rounding, > but qemu's BOOTINFOSTR()[3] and BOOTINFODATA()[4] do not. > Sorry for missing that before, I guess I was misled by the existing > bug in BOOTINFOSTR(). > > Consequently, both kexec-tools[5] and the m68k-bootinfo tool[6] cannot > parse /proc/bootinfo if the size is not a multiple of 4, which can > easily be triggered by changing the command line of the m68k virt > machine. In my brief experience in working with this structure, I've just made sure that data[] is casted to (void*) or (u8*) or something, and then everything is fine. But the tools you've linked to expect 4 byte alignment. So, it sounds like what you're saying is that while we're at it with fixing the constant, I should also make sure seed data preserves 4 byte alignment, and update the comment too? That's easy enough. I'll do that for v+1. Jason
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