Le dim. 13 août 2023, 00:57, Pedro Miguel Justo <pm...@texair.net> a écrit :
> > > > On Aug 12, 2023, at 11:04, John Paul Adrian Glaubitz < > glaub...@physik.fu-berlin.de> wrote: > > > > Hi Daniel! > > > > On Fri, 2023-08-11 at 17:31 +0200, Daniel Kiper wrote: > >> On Fri, Aug 11, 2023 at 04:10:14AM -0700, Oliver Steffen wrote: > >>> Quoting John Paul Adrian Glaubitz (2023-08-11 10:32:17) > >>>> Hi Oliver! > >>>> > >>>> On Fri, 2023-05-26 at 13:35 +0200, Oliver Steffen wrote: > >>>>> There are 3 implementations of a GUID in Grub. Replace them with a > >>>>> common one, placed in types.h. > >>>>> > >>>>> It uses the "packed" flavor of the GUID structs, the alignment > attribute > >>>>> is dropped, since it is not required. > >>>>> > >>>>> Signed-off-by: Oliver Steffen <ostef...@redhat.com> > >>>>> Reviewed-by: Daniel Kiper <daniel.ki...@oracle.com> > >> > >> [...] > >> > >>>> According to [1], this change broke GRUB on ia64: > >>>> > >>>> Welcome to GRUB! > >>>> > >>>> 7 0 0x00006B 0x000000000000001E unexpected trap > >>>> 7 0 0x000066 0x000000000000001E trap taken, number in ext PE > >>>> 7 0 0x00003C 0x0000000000005A00 trap taken, offset in ext PE > >>>> > >>>> I assume this is because of the strict alignment requirements on ia64. > >>>> > >>>> Could you have a look? > >>> > >>> I am very sorry for this mistake. > >>> My goal was to unify the two GUID types we had in grub but I missed the > >>> fact that in my "solution" the alignments are not correct in all cases. > >>> > >>> The quickest way out could be to revert the GUID unification and printf > >>> format specifier commits: > >>> > >>> 6ad116e5f guid: Make use of GUID printf format specifier > >>> f82dbf2bd kern/misc: Add a format specifier GUIDs > >>> 06edd40db guid: Unify GUID types > >>> > >>> And use the explicit, long-winded format string for printing the GUID > >>> in the bli module instead (added in the commits following those). > >>> > >>> I am open to suggestions / comments. > >> > >> Adrian, could you check what will happen when you add alignment to the > >> grub_guid_t as it was suggested by Frank here [2]? > >> > >> Personally I would avoid adding another GUID type with just alignment > >> requirement as the difference. Making one GUID type with always enforced > >> alignment should not cost us a lot. Or we can enforce alignment on EFI > >> platforms only. > > > > My Itanium hardware is not available for bootloader tests at the moment, > so I would > > like to ask Pedro Miguel Justo or Frank Scheiner to test the proposed > fix. > > > The reason that before this unification there were a packed and aligned > types suggest that the packed type was necessary in some cases. Frank had > shared the concern against his own suggestion that changing the unified > type to be aligned (as opposite to packed) would likely regress the cases > where the packed might be needed/expected. > > Just for kicks, I gave it a try: > > ``` > diff --git a/include/grub/types.h b/include/grub/types.h > index 0d96006fe..ff415c970 100644 > --- a/include/grub/types.h > +++ b/include/grub/types.h > @@ -376,7 +376,7 @@ struct grub_guid > grub_uint16_t data2; > grub_uint16_t data3; > grub_uint8_t data4[8]; > -} GRUB_PACKED; > +} __attribute__ ((aligned(8))); > typedef struct grub_guid grub_guid_t; > > #endif /* ! GRUB_TYPES_HEADER */ > ``` > > As hypothesized, there are places where these structs (now unified) are > expected to be packed, meaning to have an alignment of 1 (even smaller than > the natural alignment of its larger member). > > One of the cases where the dependency is present is in the > grub_gpt_partentry structure. This structure is packed and includes a GUID > field. One struct of an enforced alignment ’n’ cannot host a member with > enforced alignment ‘m’ where m > n. Thus, an 8 byte aligned grub_guid > cannot be hosted inside a 1 byte aligned grub_gpt_partentry: > grub_gpt_partentry doesn't need GRUB_PACKED. To be on a safe side we can add compile time assert on its size > ``` > In file included from grub-core/disk/ldm.c:26: > ./include/grub/gpt_partition.h:70:1: error: alignment 1 of ‘struct > grub_gpt_partentry’ is less than 8 [-Werror=packed-not-aligned] > 70 | } GRUB_PACKED; > | ^ > ./include/grub/gpt_partition.h:70:1: error: alignment 1 of ‘struct > grub_gpt_partentry’ is less than 8 [-Werror=packed-not-aligned] > ``` > > Now, we could go this rabbit hole on and try to hack grub_gpt_partentry, > or special-case the GUID inside grub_gpt_partentry to be packed… but at > which point will I just end up with the thing we were trying to avoid: more > than one definition of GUID? > > > > > Thanks, > > Adrian > > > > -- > > .''`. John Paul Adrian Glaubitz > > : :' : Debian Developer > > `. `' Physicist > > `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913 > >
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