* Sam Ravnborg ([EMAIL PROTECTED]) wrote: > On Thu, Jun 21, 2007 at 04:32:36PM -0400, Mathieu Desnoyers wrote: > > Hi, > > > > I just realized, working on my marker infrastructure, that a lot of > > __attribute__((section(" "))) should probably come along with an > > aligned() attribute. Since there are no data structures of size greater > > or equal to 32 bytes put in these sections later referred to by > > __sectionname_start[] and __sectionname_end[], the problem is never > > encountered (AFAIK). But as soon as these structures will reach 32 bytes > > in size, things will go ill: > > > > Let's take arch/i386/boot/video.h as an example: > > > > it defines > > > > struct card_info { > > const char *card_name; > > int (*set_mode)(struct mode_info *mode); > > int (*probe)(void); > > struct mode_info *modes; > > int nmodes; /* Number of probed modes so far */ > > int unsafe; /* Probing is unsafe, only do after "scan" > > */ > > u16 xmode_first; /* Unprobed modes to try to call anyway */ > > u16 xmode_n; /* Size of unprobed mode range */ > > }; > > > > Which is 28 bytes in size (so it is ok for now). If one single field is > > added, gcc will start aligning this structure on 32 bytes boundaries. > > (see http://gcc.gnu.org/ml/gcc-bugs/1999-11/msg00914.html) > > > > We then have > > #define __videocard struct card_info __attribute__((section(".videocards"))) > > extern struct card_info video_cards[], video_cards_end[]; > > > > Which instructs gcc to put these structures in the .videocards section. > > The linker scripts arch/i386/boot/setup.ld will assign video_cards and > > video_cards_end as pointers to the beginning and the end of this > > section. video_cards[0] is therefore expected to give the first > > structure in the section. > > The linker will align the start of the section to the biggest alignment > required by any member in the section. So gcc should tell the linker > that video_cards needs 32 bytes alignemnt and we are not facing trobles. > > BUT this requires that the labels in the linker script file are > correct assigned like this: > > .tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) { > __tracedata_start = .; > *(.tracedata) > __tracedata_end = .; > } > > If the assignment of __tracedata_start was doen just before the .tracedata > we would not use the alignment imposed by linker and would see the error you > describe. >
Hi Sam, I was experiencing problems with my addons to the DATA_DATA macro, declaring stuff in the .data section. It looked like: (vmlinux.lds.h) in -mm : /* .data section */ #define DATA_DATA \ *(.data) \ *(.data.init.refok) \ . = ALIGN(8); \ VMLINUX_SYMBOL(__start___markers) = .; \ *(__markers) \ VMLINUX_SYMBOL(__stop___markers) = .; All this is declared within the .data section. However, I could not declare a different section within this macro, because it is already placed in a section; i.e. (arch/i386/vmlinux.lds.S) in -mm : . = ALIGN(4096); .data : AT(ADDR(.data) - LOAD_OFFSET) { /* Data */ DATA_DATA CONSTRUCTORS } :data Using . = ALIGN(32); fixed my issue, but I wonder if there would be some way to express the ".tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET)" that would automatically take care of alignment within this macro? Thanks, Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/