Messages in this thread | | | Date | Thu, 5 Mar 2015 12:26:06 +0000 | From | Dave Martin <> | Subject | Re: [RFC PATCH 0/1] Wrong structure alignment due to compiler attribute "section" |
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On Wed, Mar 04, 2015 at 05:29:14PM +0100, Lino Sanfilippo wrote: > On 04.03.2015 15:35, Dave Martin wrote: > > > > >Try > > > >rm drivers/clk/mvebu/kirkwood.o > >make ARCH=arm KBUILD_CFLAGS_KERNEL=-save-temps drivers/clk/mvebu/kirkwood.o > > > >(abuse of KBUILD_CFLAGS_KERNEL here, but it's empty by default, and > >I'm too lazy to copy-paste command lines...) > > > > > >The compiler will split out the compiled assembly code in kirkwood.s: > > > >Look for ".align" directives between the start of the affected section > >and the start of the next section (next .section directive). > > > >Here, we just have .align 2, which is the expected correct value > >(i.e., align __of_table_mv88f6180_clk on a 2^2 = 4 byte boundary). > > > >A different value here may indicate a bug in the compiler, because > >you observed that gcc _thinks_ that __alignof__ is 4 for the struct > >in this section even in the failing case. > > Ok, this is the result for the assembly: > > .section __clk_of_table,"a",%progbits > .align 3 > .type __of_table_mv88f6180_clk, %object > .size __of_table_mv88f6180_clk, 196 > __of_table_mv88f6180_clk: > .space 64
[...]
> Very interesting. It shows an .align 3 which explains alignment on > 8 byte boundaries: > > > c07630f8 T __clk_of_table > c07630f8 t __of_table_fixed_factor_clk > c07630f8 T __stop_kprobe_blacklist > c07631c0 t __of_table_fixed_clk > c0763288 t __of_table_gpio_gate_clk > c0763350 t __of_table_mv88f6180_clk > > So this is indeed a compiler bug, right?
It certainly looks like the compiler is causing the issue somehow.
Whether this is a bug, a bug-like feature, a configuration issue, or a combination of these is not clear.
If you know where to find the toolchain source, it might be worth taking a look.
Cheers ---Dave
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