69 lines
1.7 KiB
Groff
69 lines
1.7 KiB
Groff
.\"
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.\" $FreeBSD$
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.\"
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.Dd December 20, 1999
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.Dt GENASSYM 8
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.Os
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.Sh NAME
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.Nm genassym
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.Nd generate assembler symbols from C
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.Sh SYNOPSIS
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.Nm genassym
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.Op Fl o Ar outfile
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.Ar objfile
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.Sh DESCRIPTION
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The
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.Nm
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command is a special-purpose program to generate assembler
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symbols from C code and is used to interface the low-level
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assembly code with the C code. This, for example, is used
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to build a FreeBSD kernel or module.
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Its
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.Ar objfile
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argument is the name of an ELF object file that holds the
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symbol definitions. These definitions are extracted from
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the object file and written to standard output or to the
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file specified with
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.Ar outfile ,
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suitable for inclusion in assembler source files.
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.Pp
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The
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.Nm
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command only extracts symbols from the object file if they
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are prefixed by
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.Nm assym_
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and are global data types, whose value is the value given
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to the symbol. The following C declaration
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.Bd -literal -offset indent -compact
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int assym_MY_SYMBOL = 3;
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.Ed
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is used to create the following assembler symbol.
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.Bd -literal -offset indent -compact
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#define MY_SYMBOL 0x3
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.Ed
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Note that the size of the symbol is extracted from the
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object file, which means that the symbol may have any type
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that is wide enough to hold the value.
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.Sh SEE ALSO
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.Xr config 8
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.Xr gensetdefs 8
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.Sh AUTHORS
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The
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.Nm
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command was written by
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.An Marcel Moolenaar Aq marcel@FreeBSD.org
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and was based on the
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.Dv gensetdefs
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command.
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.Sh BUGS
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Not all linkers store the size of the symbol in the ELF
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object file. The GNU linker for Alpha has this bug for
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example (binutils 2.9.1). In those cases the size of the
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symbol is assumed to be equal to the word size of the ELF
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object file. For Alpha this is 64 bits and for i386 this
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is 32 bits.
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.Sh HISTORY
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The
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.Nm
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command first appeared in FreeBSD 4.0.
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