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> -- 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