On i386, because of the dearth of general-purpose registers, the calling convention passes all arguments on the stack. This makes the vaarg implementation easy – A valistis simply a pointer into the stack, andvaargjust adds the size of the type to be retrieved to thevalist, and returns the old value. In fact, the i386 ABI reference simply specifiesva_arg in terms of a single line of code:

On amd64, the problem is much more complicated. To start, amd64 specifies that up to 6 integer arguments and up to 8 floating-point arguments are passed to functions in registers, to take advantage of amd64's larger number of registers. So, for a start, va_arg will have to deal with the fact that some arguments may have been passed in registers, and some on the stack.

How do we write a lot of data to disk really fast?

compile c/c++ code in assembly with an broswer

C++ is the main development language used by many of Google's open-source projects. As every C++ programmer knows, the language has many powerful features, but this power brings with it complexity, which in turn can make code more bug-prone and harder to read and maintain.

The goal of this guide is to manage this complexity by describing in detail the dos and don'ts of writing C++ code. These rules exist to keep the code base manageable while still allowing coders to use C++ language features productively.

realloc story

valgrind can run a gdb server so that a gdb can interact with it. valgrind has 2 options to trigger that:

--vgdb=yes,
--vgdb-error=0.

This second option tells valgrind it needs to wait for that many errors before freezing and wait for a gdb to connect. Setting it to 0 will make valgrind to wait for gdb to connect before executing the program.

valgrind --vgdb=yes --vgdb-error=0 ./foo
gdb ./foo
(gdb) target remote | vgdb

for i in $(objdump -d binary.o -M intel |grep "^ " |cut -f2); do echo -n '\x'$i; done;echo

One large difference between C and most other programming languages is that in C, you have to handle memory yourself rather than having a garbage collector do it for you. Ensuring that memory is allocated at the correct moment is not very difficult (and something that needs to be done manually in pretty much every language); the hard part is to ensure that enough memory is allocated, and to ensure that the memory is deallocated when it is no longer in use.

The idea behind is not only to carefully optimize produced bytecode, but also to improve its quality, and its security. Compiler warnings are critical to spot many programming errors or lethal typos that would otherwise consume days of debugging (and a big pile of money!).

Some example , how to use pseudo terminals

one file unit testing

When optimizing memory access, and memory cache misses in particular, there are surprisingly few tools to help you. valgrind’s cachegrind tool is the closest one I’ve found. It gives you a lot of information on cache misses, but not necessarily in the form you need it.

This page is about a technique for reducing the memory footprint of C programs - manually repacking C structure declarations for reduced size.