Re: IS_ERR Threshold Value

[Jan Engelhardt <jengelh@linux01.gwdg.de>]

>Subject: Re: IS_ERR Threshold Value
>
>> > Peter Anvin mentioned just a few days ago that this threshold value
>> > should be 4095 for all arches.  I think we need to get that patch
>> > done & submitted to Andrew for -mm.
>> 
>> So here the patch is:
>> 
>>  o Raise the maximum error number in IS_ERR_VALUE to 4095.
>>
>> +#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)

There seems to be a slight problem with doing that. Running
`ldd /bin/bash` prints out

	linux-gate.so.1 =>  (0xffffe000)

and the topmost address a kernel function can return is 0xFFFFf000 when 
MAX_ERRNO=4095, but that is going to be tight with the vdso mapped at 
0xffffE000.

Or is ldd giving wrong output? Because actually, `cat /proc/$$/maps` 
($$=bash) says it is mapped a lot less high:

a7fbe000-a7fbf000 r-xp a7fbe000 00:00 0          [vdso]

(CONFIG_COMPAT_VDSO=y, CONFIG_PAGE_OFFSET=0xB0000000, 2.6.18)

	-`J'
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