Kprobes build failure

[Jon Medhurst (Tixy)]

On Fri, 2014-09-26 at 00:37 +0100, Russell King - ARM Linux wrote:
> So, Olof's kbuild found this while building my rc5 based for-next tree:
> 
>         arm.allmodconfig:
> /tmp/ccoT403o.s:21439: Error: bad immediate value for offset (4168)
> /tmp/ccoT403o.s:21440: Error: bad immediate value for offset (4176)
> /tmp/ccoT403o.s:21475: Error: bad immediate value for offset (4260)
> /tmp/ccoT403o.s:21476: Error: bad immediate value for offset (4260)
> /tmp/ccoT403o.s:23566: Error: bad immediate value for offset (4132)
> /tmp/ccoT403o.s:23567: Error: bad immediate value for offset (4148)
> /tmp/ccoT403o.s:23606: Error: bad immediate value for offset (4236)
> /tmp/ccoT403o.s:23607: Error: bad immediate value for offset (4248)
> 
> which, when looking at the logs, appears to be:
> 
> /tmp/ccoT403o.s:47583: Error: bad immediate value for offset (5464)
> make[3]: *** [arch/arm/kernel/kprobes-test-arm.o] Error 1
> make[3]: Target `__build' not remade because of errors.
> make[2]: *** [arch/arm/kernel] Error 2
> 
> Any ideas?

Sounds vaguely familiar as a problem I hit before. Google finds someone
else hitting similar problem [1] and the symptoms and cause match my
memories of the old kprobe issue.

Where can I find a clue of to the config and compiler used in Olof's
build, so I can have a go at reproducing and debugging?

[1] https://lkml.org/lkml/2012/9/24/223

The relevant explanation of the above post copied below...

------------------------------------------------------------------------

The compiler uses a pretty dumb heuristic to guess the size of asms:
4 * (number of ; or \n in the string)

Directives that the compiler can't predict the size of are not safe if
they output into any segment that the compiler uses.  .fill/.skip are
obvious candidates, but macro expansions, .rept, .irp etc. can cause
these problems too.

For example:

	void g(int);
	void f(void)
	{
		g(0xd00dfeed);
		asm(".skip 0x1000");
	}
If you try building this with gcc -marm -Os for example:

/tmp/ccXYm1uP.s: Assembler messages:
/tmp/ccXYm1uP.s:21: Error: bad immediate value for offset (4100)

...because the assembler assumes that it can dump a literal at the end
of the function and reference it from the g() callsite.

------------------------------------------------------------------------


-- 
Tixy