Alignment of LinuxBIOS table structures
stepan at openbios.org
Tue Nov 30 03:24:00 CET 2004
* Eric W. Biederman <ebiederman at lnxi.com> [041129 19:21]:
> To see what the problem actually amounts to I walked through my
> compiler collection with a simple test to see what sizeof reported
> for lb_memory_range, (without adding the packed attribute).
> On 32bit x86 I tested with:
> And in each instance the result was 20.
> So from what I can see with 32bit x86 code we are consistent, and we
> do not have compiler version dependencies. So the bad definition
> is consistent.
x86 QNX/Neutrino 6.2.1 (with gcc 2.95.3):
# gcc -v
Reading specs from /usr/lib/gcc-lib/ntox86/2.95.3qnx-nto/specs
gcc version 2.95.3qnx-nto 20010315 (release)
sizeof(struct lb_memory): 8
It seems gcc does not always behave the same.
> It is a good pragmatic solution, but actually needing __attribute__ ((packed))
> is an issue. As Ron has pointed out, not all compilers support it.
> And having a definition that varies between 32bit and 64bit is a
> problem anyway.
So you are saying people out there are building LinuxBIOS with non-gnu
compilers? I actually doubt that, assuming a lot of objcopy/objdump/ld
magic is pretty much gnu specific as well..
one could go like:
#define STRICTSIZE __attribute__ ((packed))
Fixing the issue among all gcc versions while not breaking anything on
others. It really sucks that gcc does magic here that makes writing
portable code really ugly.
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