* David Miller (davem@xxxxxxxxxxxxx) wrote: > From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > Date: Fri, 21 Jan 2011 15:36:32 -0500 > > > Problem description: > > > > gcc happily align structures defined statically on 32-byte. Ftrace trace events > > and Tracepoints both statically define structures into sections (using the > > "section" attribute), to then assign these to symbols with the linker scripts to > > iterate the these sections as an array. > > > > However, gcc uses different alignments for these structures when they are > > defined statically and when they are globally visible and/or in an array. > > Therefore iteration on these arrays sees "holes" of padding. > > > > Use the __u64_aligned for type declarations and variable definitions to ensure > > that gcc: > > > > a) iterates on the correctly aligned type. (type attribute) > > b) generates the definitions within the sections with the appropriate alignment. > > (variable attribute) > > > > The Ftrace code introduced the "aligned(4)" variable attribute in commit > > 1473e4417c79f12d91ef91a469699bfa911f510f to try to work around this problem that > > showed up on x86_64, but it causes unaligned accesses on sparc64, and is > > generally a bad idea on 64-bit if RCU pointers are contained within the > > structure. Moreover, it did not use the same attribute as type attribute, which > > could cause the iteration on the extern array structure not to match the > > variable definitions for some structure sizes. > > > > We should also ensure proper alignment of each Ftrace section in > > include/asm-generic/vmlinux.lds.h. > > > > Moving all STRUCT_ALIGN() for FTRACE_EVENTS() and TRACE_SYSCALLS() into the > > definitions, so the alignment is only done if these infrastructures are > > configured in. Use U64_ALIGN instead of STRUCT_ALIGN. > > > > Also align TRACE_PRINTKS on U64_ALIGN to make sure the beginning of the section > > is aligned on pointer size. > > > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > > Acked-by: David S. Miller <davem@xxxxxxxxxxxxx> Thanks! This patch, just like 1/3, should also go into -stable, for both .36 and .37. As I'm thinking, the following patch (for Tracepoints) should only go into the -tip tree, as it does not fix a problem -- it merely reduces the data footprint of the tracepoints structures. I'm therefore not forwarding patch 3/3 for inclusion into -stable. Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
