Chapter 5 C programming expert thinking 5.4 alert Interpositioning of links

Interpositioning (some people call it "interposing") replaces the behavior of a library function by writing a function with the same name as the library function.Not only will all calls to this library function that you make yourself will be replaced by your own version of the function call, but all system calls that call the library function will also be replaced by your function.Interpositioning itself is not a bug, it is explicitly required by the compiler to support it.

Do not make any symbols in a program global unless they are intended to be one of the program's interfaces.
mktemp has now been replaced by the ANSI C standard library function tmpname.

The listed identifiers should not appear in the declarations of their own programs.Some of these identifiers are always reserved, others are only reserved if a specific header file is included.Some identifiers are reserved only at the global scope, others are reserved both at the global scope and at the file scope.Also note that all keywords are reserved.The easiest way to avoid trouble is to think that these identifiers are always owned by the system and not use them as their own.

Several items look like this: is[a-z]anything
This means anything starting with "is" followed by a lowercase letter from a to z (but not including things like numbers),Then follow any character.
A few more items look like this: acos, -f, -l.
It means that the 3 identifiers acos, acosf, acosl are reserved.All functions located in the math header file have a basic version that accepts a double argument.There may be two additional versions there: the base name with the suffix l means that the function accepts a long double parameter: the base name with the suffix f means the function accepts a float parameter.

Section 6.1.2 of the ANSI C standard specifies that for external identifiers, the compiler can define itself to make them case-insensitive.At the same time, the first 6 characters of external identifiers must be different from other identifiers (ANSI C standard section 5.2.4.1, "Compile restrictions").There are also some symbols to avoid for other libraries that are linked.You should check the ABI documentation to see which identifiers to avoid.
If the identifier is reserved, it means that the user cannot redefine it.However, this is not a constraint.When this happens, it doesn't ask the compiler to give an error message.It just caused some non-portability issues or undefined behavior.

You can use the -m option in the ld program to have the compiler generate a report.It contains a description of the symbols being Interposed.Normally, ld with the -m option produces a memory map or list showing where those symbols are placed in the executable.It shows multiple instances of the same symbol at the same time, and by looking at the contents of the report, the user can tell if Interpositioning has occurred.
The -D option in the ld program was introduced with SunOS 5.3 to provide better link-edit debugging.This option allows the user to display the link-edit process and the included input files.This option is especially useful if you need to monitor the process of extracting objects from the archive.It can also be used to display runtime binding information.
Description of ld complex program:
* Use the ldd command to list the dynamic set of dependencies of an executable.This command will tell you the function library required by the dynamically linked program
*The -Dhelp option of the ld program can provide some information to help find problems during the linking process:
*View the online of the ld programDocumentation;
*Read SunOs Linker and Libraries Manual