Re: Average instruction length in x86-built kernel?

From: Karim Yaghmour
Date: Sat Jul 30 2005 - 15:06:12 EST

Hello Ingo,

Ingo Oeser wrote:
> Just study the output od objdump -d and average the differences
> of the first hex number in a line printed, which are followed by a ":"

Here's a script that does what I was looking for:

# Dissassemble
objdump -d $1 -j .text > $2-dissassembled-kernel

# Remove non-instruction lines:
sed /^[^c].*/d $2-dissassembled-kernel > $2-stage-1

# Remove empty lines:
sed /^'\t'*$/d $2-stage-1 > $2-stage-2

# Remove function names:
sed /^c[0-9,a-f]*' '\<.*\>:$/d $2-stage-2 > $2-stage-3

# Remove addresses:
sed s/^c[0-9,a-f]*:'\t'// $2-stage-3 > $2-stage-4

# Remove instruction text:
sed s/'\t'.*// $2-stage-4 > $2-stage-5

# Remove trailing whitespace:
sed s/'\s'*$// $2-stage-5 > $2-stage-6

# Separate instructions depending on size:
egrep "([0-9a-f]{2}[' ']*){5}" $2-stage-6 > $2-more-or-eq-5
egrep "^([0-9a-f]{2}[' ']*){0,4}$" $2-stage-6 > $2-less-or-eq-4

# Find out how much of each we've got:
wc -l $2-stage-6
wc -l $2-more-or-eq-5
wc -l $2-less-or-eq-4

The last part can easily be changed to iterate through and separate
those that are 1 byte, 2 bytes, etc. and automatically come up with
stats, but this was fine for what I was looking for.

I ran it on a 2.4.x and a 2.6.x kernel and about 3/4 of instructions
are 4 bytes or less.

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