148 lines
2.6 KiB
Plaintext
148 lines
2.6 KiB
Plaintext
.TH MEMORY 2
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.SH NAME
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memccpy, memchr, memcmp, memcpy, memmove, memset, tsmemcmp \- memory operations
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLvoid* 'u
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.B
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void* memccpy(void *s1, void *s2, int c, usize n)
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.PP
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.B
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void* memchr(void *s, int c, usize n)
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.PP
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.B
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int memcmp(void *s1, void *s2, usize n)
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.PP
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.B
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void* memcpy(void *s1, void *s2, usize n)
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.PP
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.B
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void* memmove(void *s1, void *s2, usize n)
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.PP
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.B
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void* memset(void *s, int c, usize n)
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.PP
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.B #include <libsec.h>
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.PP
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.B
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int tsmemcmp(void *s1, void *s2, ulong n)
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.SH DESCRIPTION
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These functions operate efficiently on memory areas
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(arrays of bytes bounded by a count, not terminated by a zero byte).
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They do not check for the overflow of any receiving memory area.
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.PP
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.I Memccpy
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copies bytes from memory area
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.I s2
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into
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.IR s1 ,
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stopping after the first occurrence of byte
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.I c
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has been copied, or after
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.I n
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bytes have been copied, whichever comes first.
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It returns a pointer to the byte after
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the copy of
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.I c
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in
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.IR s1 ,
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or zero if
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.I c
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was not found in the first
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.I n
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bytes of
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.IR s2 .
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.PP
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.I Memchr
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returns a pointer to the first
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occurrence of byte
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.I c
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in the first
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.I n
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bytes of memory area
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.IR s,
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or zero if
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.I c
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does not occur.
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.PP
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.I Memcmp
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compares its arguments, looking at the first
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.I n
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bytes only, and returns an integer
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less than, equal to, or greater than 0,
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according as
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.I s1
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is lexicographically less than, equal to, or
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greater than
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.IR s2 .
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The comparison is bytewise unsigned.
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.PP
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.I Memcpy
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copies
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.I n
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bytes from memory area
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.I s2
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to
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.IR s1 .
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It returns
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.IR s1 .
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.PP
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.I Memmove
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works like
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.IR memcpy ,
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except that it is guaranteed to work if
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.I s1
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and
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.IR s2
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overlap.
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.PP
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.I Memset
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sets the first
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.I n
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bytes in memory area
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.I s
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to the value of byte
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.IR c .
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It returns
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.IR s .
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.PP
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.I Tsmemcmp
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is a variant of
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.I memcmp
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that is safe against timing attacks.
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It does not stop when it sees a difference, this way it's runtime is function of
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.I n
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and not something that can lead clues to attackers.
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.SH SOURCE
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All these routines have portable C implementations in
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.BR /sys/src/libc/port .
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Most also have machine-dependent assembly language implementations in
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.BR /sys/src/libc/$objtype .
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.I Tsmemcmp
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is found on
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.BR /sys/src/libsec/port/tsmemcmp.c .
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.SH SEE ALSO
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.IR strcat (2)
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.SH BUGS
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ANSI C does not require
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.I memcpy
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to handle overlapping source and destination; on Plan 9, it does, so
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.I memmove
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and
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.I memcpy
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behave identically.
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.PP
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If
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.I memcpy
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and
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.I memmove
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are handed a negative count, they abort.
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.PP
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.I Memcmp
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should not be used to compare sensitive data as it's vulnerable to timing attacks. Instead,
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.I tsmemcmp
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should be used.
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