From 673b0d84ba9591e07c0bdf0ee49d92eba10f502c Mon Sep 17 00:00:00 2001 From: Matthew Burgess Date: Mon, 3 May 2004 10:59:46 +0000 Subject: * Merged newxml into HEAD git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@3435 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689 --- chapter05/chapter05.xml | 462 ++++-------------------------------------------- 1 file changed, 38 insertions(+), 424 deletions(-) (limited to 'chapter05/chapter05.xml') diff --git a/chapter05/chapter05.xml b/chapter05/chapter05.xml index f8724b46b..9a939e00e 100644 --- a/chapter05/chapter05.xml +++ b/chapter05/chapter05.xml @@ -1,428 +1,42 @@ + + + %general-entities; +]> + Constructing a temporary system - - - - -Introduction - - -In this chapter we will compile and install a minimal -Linux system. This system will contain just enough tools to be able -to start constructing the final LFS system in the next chapter. - -The building of this minimal system is done in two steps: first we -build a brand-new and host-independent toolchain (compiler, assembler, -linker and libraries), and then use this to build all the other essential -tools. - -The files compiled in this chapter will be installed under the -$LFS/tools directory -to keep them separate from the files installed in the next chapter. -Since the packages compiled here are merely temporary, we don't want -them to pollute the soon-to-be LFS system. - -Before issuing the build instructions for a package you are expected to -have already unpacked it as user lfs, and to have -performed a cd into the created directory. The build -instructions assume that you are using the bash -shell. - -Several of the packages are patched before compilation, but only when -the patch is needed to circumvent a problem. Often the patch is needed in -both this and the next chapter, but sometimes in only one of them. Therefore, -don't worry when instructions for a downloaded patch seem to be missing. Also, -when applying a patch, you'll occasionally see warning messages about -offset or fuzz. These warnings are -nothing to worry about, as the patch was still successfully applied. - -During the compilation of most packages you will see many warnings -scroll by on your screen. These are normal and can safely be ignored. They are -just what they say they are: warnings -- mostly about deprecated, but not -invalid, use of the C or C++ syntax. It's just that C standards have changed -rather often and some packages still use the older standard, which is not -really a problem. - -After installing each package you should delete its source and build -directories, unless told otherwise. Deleting the sources -saves space, but also prevents misconfiguration when the same package is -reinstalled further on. Only for three packages you will need to keep the -source and build directories around for a while, so their contents can be used -by later commands. Do not miss the reminders. - - - - - -Technical notes - - -This section attempts to explain some of the rationale and technical -details behind the overall build method. It's not essential that you understand -everything here immediately. Most of it will make sense once you have performed -an actual build. Feel free to refer back here at any time. - -The overall goal of is to provide a sane, -temporary environment that we can chroot into, and from which we can produce a -clean, trouble-free build of the target LFS system in -. Along the way, we attempt to divorce ourselves -from the host system as much as possible, and in so doing build a -self-contained and self-hosted toolchain. It should be noted that the -build process has been designed in such a way so as to minimize the risks for -new readers and provide maximum educational value at the same time. In other -words, more advanced techniques could be used to build the system. - - -Before continuing, you really should be aware of the name of your working -platform, often also referred to as the target triplet. For -many folks the target triplet will probably be -i686-pc-linux-gnu. A simple way to determine your target -triplet is to run the config.guess script that comes with -the source for many packages. Unpack the Binutils sources and run the script: -./config.guess and note the output. - -You'll also need to be aware of the name of your platform's -dynamic linker, often also referred to as the -dynamic loader, not to be confused with the standard linker -ld that is part of Binutils. The dynamic linker is provided -by Glibc and has the job of finding and loading the shared libraries needed by a -program, preparing the program to run and then running it. For most folks the -name of the dynamic linker will be ld-linux.so.2. On -platforms that are less prevalent, the name might be -ld.so.1 and newer 64 bit platforms might even have -something completely different. You should be able to determine the name -of your platform's dynamic linker by looking in the -/lib directory on your host system. A -surefire way is to inspect a random binary from your host system by running: -readelf -l <name of binary> | grep interpreter -and noting the output. The authoritative reference covering all platforms is in -the shlib-versions file in the root of the Glibc source -tree. - - -Some key technical points of how the build -method works: - - -Similar in principle to cross compiling whereby tools installed -into the same prefix work in cooperation and thus utilize a little GNU -"magic". - -Careful manipulation of the standard linker's library search -path to ensure programs are linked only against libraries we -choose. - -Careful manipulation of gcc's -specs file to tell the compiler which target dynamic -linker will be used. - - -Binutils is installed first because both GCC and Glibc perform various -feature tests on the assembler and linker during their respective runs of -./configure to determine which software features to enable -or disable. This is more important than one might first realize. An incorrectly -configured GCC or Glibc can result in a subtly broken toolchain where the impact -of such breakage might not show up until near the end of the build of a whole -distribution. Thankfully, a test suite failure will usually alert us before too -much time is wasted. - -Binutils installs its assembler and linker into two locations, -/tools/bin and -/tools/$TARGET_TRIPLET/bin. In reality, -the tools in one location are hard linked to the other. An important facet of -the linker is its library search order. Detailed information can be obtained -from ld by passing it the --verbose -flag. For example: ld --verbose | grep SEARCH will -show you the current search paths and their order. You can see what files are -actually linked by ld by compiling a dummy program and -passing the --verbose switch to the linker. For example: -gcc dummy.c -Wl,--verbose 2>&1 | grep succeeded -will show you all the files successfully opened during the linking. - -The next package installed is GCC and during its run of -./configure you'll see, for example: - -
checking what assembler to use... /tools/i686-pc-linux-gnu/bin/as -checking what linker to use... /tools/i686-pc-linux-gnu/bin/ld
- -This is important for the reasons mentioned above. It also demonstrates -that GCC's configure script does not search the PATH directories to find which -tools to use. However, during the actual operation of gcc -itself, the same search paths are not necessarily used. You can find out which -standard linker gcc will use by running: -gcc -print-prog-name=ld. -Detailed information can be obtained from gcc by passing -it the -v flag while compiling a dummy program. For -example: gcc -v dummy.c will show you detailed -information about the preprocessor, compilation and assembly stages, including -gcc's include search paths and their order. - -The next package installed is Glibc. The most important considerations for -building Glibc are the compiler, binary tools and kernel headers. The compiler -is generally no problem as Glibc will always use the gcc -found in a PATH directory. The binary tools and kernel headers can be a little -more troublesome. Therefore we take no risks and use the available configure -switches to enforce the correct selections. After the run of -./configure you can check the contents of the -config.make file in the -glibc-build directory for all the -important details. You'll note some interesting items like the use of -CC="gcc -B/tools/bin/" to control which binary tools are -used, and also the use of the -nostdinc and --isystem flags to control the compiler's include search -path. These items help to highlight an important aspect of the Glibc package: -it is very self-sufficient in terms of its build machinery and generally does -not rely on toolchain defaults. - -After the Glibc installation, we make some adjustments to ensure that -searching and linking take place only within our /tools -prefix. We install an adjusted ld, which has a hard-wired -search path limited to /tools/lib. Then -we amend gcc's specs file to point to our new dynamic -linker in /tools/lib. This last step is -vital to the whole process. As mentioned above, a -hard-wired path to a dynamic linker is embedded into every ELF shared -executable. You can inspect this by running: -readelf -l <name of binary> | grep interpreter. -By amending gcc's specs file, we are ensuring that every -program compiled from here through the end of this chapter will use our new -dynamic linker in /tools/lib. - -The need to use the new dynamic linker is also the reason why we apply the -Specs patch for the second pass of GCC. Failure to do so will result in the GCC -programs themselves having the name of the dynamic linker from the host system's -/lib directory embedded into them, which -would defeat our goal of getting away from the host. - -During the second pass of Binutils, we are able to utilize the ---with-lib-path configure switch to control -ld's library search path. From this point onwards, the -core toolchain is self-contained and self-hosted. The remainder of the - packages all build against the new Glibc in -/tools and all is well. - -Upon entering the chroot environment in , the -first major package we install is Glibc, due to its self-sufficient nature that -we mentioned above. Once this Glibc is installed into -/usr, we perform a quick changeover of -the toolchain defaults, then proceed for real in building the rest of the -target LFS system. - -
- - - -Notes on static linking - - -Most programs have to perform, beside their specific task, many rather -common and sometimes trivial operations. These include allocating memory, -searching directories, reading and writing files, string handling, pattern -matching, arithmetic and many other tasks. Instead of obliging each program to -reinvent the wheel, the GNU system provides all these basic functions in -ready-made libraries. The major library on any Linux system is -Glibc. - -There are two primary ways of linking the functions from a library to a -program that uses them: statically or dynamically. When a program is linked -statically, the code of the used functions is included in the executable, -resulting in a rather bulky program. When a program is dynamically linked, what -is included is a reference to the dynamic linker, the name of the library, and -the name of the function, resulting in a much smaller executable. (A third way -is to use the programming interface of the dynamic linker. See the -dlopen man page for more information.) - -Dynamic linking is the default on Linux and has three major advantages -over static linking. First, you need only one copy of the executable library -code on your hard disk, instead of having many copies of the same code included -into a whole bunch of programs -- thus saving disk space. Second, when several -programs use the same library function at the same time, only one copy of the -function's code is required in core -- thus saving memory space. Third, when a -library function gets a bug fixed or is otherwise improved, you only need to -recompile this one library, instead of having to recompile all the programs that -make use of the improved function. - -If dynamic linking has several advantages, why then do we statically link -the first two packages in this chapter? The reasons are threefold: historical, -educational, and technical. Historical, because earlier versions of LFS -statically linked every program in this chapter. Educational, because knowing -the difference is useful. Technical, because we gain an element of independence -from the host in doing so, meaning that those programs can be used -independently of the host system. However, it's worth noting that an overall -successful LFS build can still be achieved when the first two packages are -built dynamically. - - - - -&c5-binutils-pass1; -&c5-gcc-pass1; -&c5-kernelheaders; -&c5-glibc; - - - -Adjusting the toolchain - - -Now that the temporary C libraries have been installed, we want all -the tools compiled in the rest of this chapter to be linked against these -libraries. To accomplish this, we need to adjust the linker and the compiler's -specs file. Some people would say that it is "black magic juju below -this line", but it is really very simple. - -First install the adjusted linker (adjusted at the end of the first pass -of Binutils) by running the following command from within -the binutils-build directory: - -make -C ld install - -From this point onwards everything will link only -against the libraries in /tools/lib. - -If you somehow missed the earlier warning to retain the Binutils -source and build directories from the first pass or otherwise accidentally -deleted them or just don't have access to them, don't worry, all is not lost. -Just ignore the above command. The result is a small chance of the subsequent -testing programs linking against libraries on the host. This is not ideal, but -it's not a major problem. The situation is corrected when we install the -second pass of Binutils a bit further on. - -Now that the adjusted linker is installed, you have to -remove the Binutils build and source directories. - -The next thing to do is to amend our GCC specs file so that it points -to the new dynamic linker. A simple sed will accomplish this: - - - -SPECFILE=/tools/lib/gcc-lib/*/*/specs && -sed -e 's@ /lib/ld-linux.so.2@ /tools/lib/ld-linux.so.2@g' \ -    $SPECFILE > tempspecfile && -mv -f tempspecfile $SPECFILE && -unset SPECFILE - -We recommend that you cut-and-paste the above rather than try and type it -all in. Or you can edit the specs file by hand if you want to: just replace the -occurrence of "/lib/ld-linux.so.2" with "/tools/lib/ld-linux.so.2". Be sure to -visually inspect the specs file to verify the intended change was actually -made. - -If you are working on a platform where the name of the dynamic -linker is something other than ld-linux.so.2, you -must substitute ld-linux.so.2 with the -name of your platform's dynamic linker in the above commands. Refer back to - if necessary. - -Lastly, there is a possibility that some include files from the host -system have found their way into GCC's private include dir. This can happen -because of GCC's "fixincludes" process which runs as part of the GCC build. -We'll explain more about this further on in this chapter. For now, run the -following commands to eliminate this possibility: - -rm -f /tools/lib/gcc-lib/*/*/include/{pthread.h,bits/sigthread.h} - - - - -It is imperative at this point to stop and ensure that the basic -functions (compiling and linking) of the new toolchain are working as expected. -For this we are going to perform a simple sanity check: - -echo 'main(){}' > dummy.c -cc dummy.c -readelf -l a.out | grep ': /tools' - -If everything is working correctly, there should be no errors, and the -output of the last command will be (allowing for platform specific differences -in dynamic linker name): - -
[Requesting program interpreter: /tools/lib/ld-linux.so.2]
- -Note especially that /tools/lib -appears as the prefix of our dynamic linker. - -If you did not receive the output -as shown above, or received no output at all, then something is seriously wrong. -You will need to investigate and retrace your steps to find out where the -problem is and correct it. There is no point in continuing until this is done. -First, redo the sanity check using gcc instead of -cc. If this works it means the -/tools/bin/cc symlink is missing. Revisit - and fix the symlink. Second, ensure your PATH -is correct. You can check this by running echo $PATH and -verifying that /tools/bin is at the head -of the list. If the PATH is wrong it could mean you're not logged in as user -lfs or something went wrong back in . Third, something may have gone wrong -with the specs file amendment above. In this case redo the specs file amendment -ensuring to cut-and-paste the commands as was recommended. - -Once you are satisfied that all is well, clean up the test files: - -rm dummy.c a.out -
- - - - -
- - -&c5-tcl; -&c5-expect; -&c5-dejagnu; -&c5-gcc-pass2; -&c5-binutils-pass2; - -&c5-gawk; -&c5-coreutils; -&c5-bzip2; -&c5-gzip; -&c5-diffutils; -&c5-findutils; -&c5-make; -&c5-grep; -&c5-sed; -&c5-gettext; -&c5-ncurses; -&c5-patch; -&c5-tar; -&c5-texinfo; -&c5-bash; -&c5-perl; - - - -Stripping - - -The steps in this section are optional, but if your LFS partition is -rather small, you will be glad to learn that you can remove some unnecessary -things. The executables and libraries you have built so far contain about 130 -MB of unneeded debugging symbols. Remove those symbols with: - -strip --strip-debug /tools/lib/* -strip --strip-unneeded /tools/{,s}bin/* - -The last of the above commands will skip some twenty files, reporting -that it doesn't recognize their file format. Most of them are scripts instead -of binaries. - -Take care not to use ---strip-unneeded on the libraries -- the static ones -would be destroyed and you would have to build the three toolchain packages -all over again. - -To save another 30 MB, you can remove all the documentation: - -rm -rf /tools/{doc,info,man} - -You will now need to have at least 850 MB of free space on your LFS -file system to be able to build and install Glibc in the next phase. If you can -build and install Glibc, you can build and install the rest too. - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
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