Date: Thu, 20 Nov 2014 12:33:33 -0200 From: =?UTF-8?Q?fran=C3=A7ai_s?= <romapera15@gmail.com> To: freebsd-emulation@freebsd.org Subject: This topic is mainly for developers of FreeBSD that develop in machine code, until even in binary code. Message-ID: <CAK_6RweXftPPitkRmOkZQOYvaKrA1FNrfpgqcJLidwgATmZFGA@mail.gmail.com>
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This subject is irresistible to me,I like so much of this issue that get out tears out of my eyes. This topic is mainly for developers of FreeBSD that develop in machine code, until even in binary code. A FreeBSD developer told me via private message that the the most FreeBSD developers don=E2=80=99t develop in machine code, in other words, the mino= rity FreeBSD developers develop in machine code, until even in binary code. He told me this: "We either create a macro expands to something like ".word <foo> =E2=80=9C = or sometimes the .word <foo> is just hard coded inline when there=E2=80=99s on= ly going to be one of them. Sometimes we expose them both in assembly and in C code, in which case what we do varies a bit to accommodate the different language=E2=80=99s syntax. It is rare, but has happened, that we only expos= e it to C code. Generally, though, we try to add support for the opcodes to gas so that we get the constraint testing it does (making sure the opcode is supported at the level you are compiling, making sure it isn=E2=80=99t in a delay slot o= r violating some other precondition for its use)." "You pointed me at macros that defined operations in terms of opcodes the assembler didn=E2=80=99t understand with the workaround being the assembler directive using .word followed by by some hex value to encode the opcode." "Most developers of FreeBSD don=E2=80=99t write directly in machine code i= n FreeBSD development, and don=E2=80=99t care. Some developers use the marcos= that I described sometimes when doing specific, low-level coding. A handful of developers create the marcos directly or use the .word directives in their work to make certain things work that cannot work otherwise. People generally don=E2=80=99t write in raw machine opcodes. That is indepe= ndent of FreeBSD. However, a few, specialized people will find the need to do it from time to time. Usually because they are porting FreeBSD to a newer processor that needs newer opcodes to do context switching, optimize interrupt handling, code with a new type of cache coherency, etc. These people look up the assembler in the docs from the vendor and then create the .word workaround to make sure things work. If they have the time, they may add it to our somewhat ancient gas assembler as well." "Almost nobody writes directly in binary. There are some exceptions, sometimes though." The following link leads to tutorial that teaches programming Assembly in to FreeBSD: http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/x86.ht= ml Also exist tutorial that teaches programming in machine code to FreeBSD?
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