Cirrus Logic CS485 Instrukcja Użytkownika Pobierz pdf (Strona 39)

CS485G Spring 2015 39

42 Interpositioning

1. Replace standard routine with a special one in order to monitor (for

example, to ﬁnd memory leaks), proﬁle (for improving efﬁciency),

add facility (like encryption), reduce facility (sandboxing).

2. At compile time: Build replacement, and use #define to force calls

to go to the replacement.

3. At link time: build replacement version wrap foo() that calls

real foo() when it needs it. Call the linker with --wrap,foo.

Gcc can pass this ﬂag to the linker: -Wl,--wrap,foo. Then the

linker resolves calls to foo() as wrap foo() and calls to real foo()

as foo().

4. At load time: tell dynamic linker to resolve symbols by going ﬁrst to

a special library. The dynamic linker uses the LD PRELOAD environ-

ment variable:

LD_PRELOAD="/usr/lib64/libdl.so ./mymalloc.so"

./myProg

43 Operating systems — Introduction

1. Lecture 23, 3/27/2015 Lab 5

2. Lecture 24, 3/30/2015

3. Goals

(a) abstract the hardware, hiding some features and providing new

ones.

(b) share resources among processes.

4. Layers

(a) Hardware, including instruction set, registers, memory, and de-

vices.

(b) OS kernel

5. Kernel design alternatives

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Cirrus Logic CS485 Instrukcja Użytkownika Strona 39