commit/plan9port: 2 new changesets

[Bitbucket]

2 new commits in plan9port:

https://bitbucket.org/rsc/plan9port/commits/3cd53e993790/
changeset: 3cd53e993790
user: xiw
date: 2013-03-19 19:35:16
summary: libsec: avoid undefined C

gcc compiles `p + length < p' into 'length < 0' since pointer overflow is undefined behavior in C. This breaks the check against a large `length'.

Use `length > pend - p' instead.

There's no need to check `length < 0' since `length' is from length_decode() and should be non-negative.

===

Try the simplified code.

void bar(void);
void foo(unsigned char *p, int length)
{
if (p + length < p)
bar();
}

$ gcc -S -o - t.c -O2
...
foo:
.LFB0:
.cfi_startproc
testl %esi, %esi
js .L4
rep
ret
.L4:
jmp bar
.cfi_endproc

Clearly `p' is not used at all.

R=rsc
CC=plan9port.codebot
https://codereview.appspot.com/7231069

Committer: Russ Cox <r...@swtch.com>
affected #: 1 file

https://bitbucket.org/rsc/plan9port/commits/1bd8b25173d5/
changeset: 1bd8b25173d5
user: xiw
date: 2013-03-19 19:36:50
summary: rc: avoid undefined C

There are two bugs in pdec() on INT_MIN:

* wrong output.

`n = 1-n' should be `n = -1-n' when n is INT_MIN.

* infinite loop.

gcc optimizes `if(n>=0)' into `if(true)' because `-INT_MIN' (signed integer overflow) is undefined behavior in C, and gcc assumes the negation of a negative number must be positive. The resulting binary keeps printing '-' forever given INT_MIN.

Try the simplified pdec.c below.

$ gcc pdec.c
$ ./a.out -2147483648
--214748364*

$ gcc pdec.c -O2
$ ./a.out -2147483648
<infinite loop>

$ gcc pdec.c -O2 -D__PATCH__
$ ./a.out -2147483648
-2147483648

=== pdec.c ===

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

#define io void

void pchr(io *f, int c)
{
putchar(c);
}

void pdec(io *f, int n)
{
if(n<0){
#ifndef __PATCH__
n=-n;
if(n>=0){
pchr(f, '-');
pdec(f, n);
return;
}
/* n is two's complement minimum integer */
n = 1-n;
#else
if(n!=INT_MIN){
pchr(f, '-');
pdec(f, -n);
return;
}
/* n is two's complement minimum integer */
n = -(INT_MIN+1);
#endif
pchr(f, '-');
pdec(f, n/10);
pchr(f, n%10+'1');
return;
}
if(n>9)
pdec(f, n/10);
pchr(f, n%10+'0');
}

int main(int argc, char **argv)
{
int n = atoi(argv[1]);
pdec(NULL, n);
putchar('\n');
}

R=rsc
CC=plan9port.codebot
https://codereview.appspot.com/7241055

Committer: Russ Cox <r...@swtch.com>
affected #: 1 file

Repository URL: https://bitbucket.org/rsc/plan9port/

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