FreeBSD src
2bae1ab6a5
When reading the code I had to stop, say "ok, what does *these* modifications of strl*() do? Pull out grep. Oh, not in add/, maybe above in ../lib/? Yep. So what do they do? Comments above them are misleading, guess I'll have to read the code. Oh, they just test strl* against the size and return the result of the test. Now I can continue to read the code I was. The uses of s_strl*() then test that result and errx()'s. Lets think about the "optimized" code I am removing: In general the compiler pushes the three args to strl* onto the stack and calls s_strl*. s_strl* has to indirectly access 3 args from the stack. Then push them on the stack a 2nd time for the real strl* call. s_strl* then pops the return from strl* off the stack; or moves it from the register it was returned in, to the register where tests can happen. s_strl* then pops the three arguments to strl*. Perform the test, push the result of the test, or move it from the result register to the return value register. The caller to s_strl* now has to either pop the return value of s_strl* or move it from the return value register to the test register. The caller then pops the three args to s_strl* off the stack (the same args that s_strl* itself had to pop off after the real call to strl*). The s_strl* caller then performs a simular test to what has already been done, and conditionally jumps. By doing things this way, we've given the compiler optimizer less to work with. Also, please don't forget the that call to s_strl* has possibly jumped to code not in the cache due to being far away from the calling code, thus causing a pipeline stall. So where is the "optimization" from s_strl*? It isn't code clarity. It isn't code execution speed. It isn't code size either. |
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| bin | ||
| contrib | ||
| crypto | ||
| etc | ||
| games | ||
| gnu | ||
| include | ||
| kerberos5 | ||
| kerberosIV | ||
| lib | ||
| libexec | ||
| release | ||
| sbin | ||
| secure | ||
| share | ||
| sys | ||
| tools | ||
| usr.bin | ||
| usr.sbin | ||
| COPYRIGHT | ||
| Makefile | ||
| Makefile.inc1 | ||
| Makefile.upgrade | ||
| README | ||
| UPDATING | ||
This is the top level of the FreeBSD source directory. This file was last revised on: $FreeBSD$ For copyright information, please see the file COPYRIGHT in this directory (additional copyright information also exists for some sources in this tree - please see the specific source directories for more information). The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree, the most commonly used one being ``world'', which rebuilds and installs everything in the FreeBSD system from the source tree except the kernel, the kernel-modules and the contents of /etc. The ``buildkernel'' and ``installkernel'' targets build and install the kernel and the modules (see below). Please see the top of the Makefile in this directory for more information on the standard build targets and compile-time flags. Building a kernel is a somewhat more involved process, documentation for which can be found at: http://www.freebsd.org/handbook/kernelconfig.html And in the config(8) man page. Note: If you want to build and install the kernel with the ``buildkernel'' and ``installkernel'' targets, you have to build world before. More information is available in the handbook. The sample kernel configuration files reside in the sys/i386/conf sub-directory (assuming that you've installed the kernel sources), the file named GENERIC being the one used to build your initial installation kernel. The file NOTES contains entries and documentation for all possible devices, not just those commonly used. It is the successor of the ancient LINT file, but in contrast to LINT, it is not buildable as a kernel but a pure reference and documentation file. Source Roadmap: --------------- bin System/User commands. contrib Packages contributed by 3rd parties. crypto Cryptography stuff (see crypto/README). etc Template files for /etc games Amusements. gnu Various commands and libraries under the GNU Public License. Please see gnu/COPYING* for more information. include System include files. kerberosIV Kerberos package. lib System libraries. libexec System daemons. release Release building Makefile & associated tools. sbin System commands. secure Cryptographic libraries and commands. share Shared resources. sys Kernel sources. tools Utilities for regression testing and miscellaneous tasks. usr.bin User commands. usr.sbin System administration commands. For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see: http://www.freebsd.org/handbook/synching.html