tree 054259e5f4ee1c94e0afde8fbf0fb518940e5264
parent 01e3847b7e6ff87f72a34a42cd98425e569250f6
author Xi Wang <xi.wang@gmail.com> 1363718116 -0400
committer Russ Cox <rsc@swtch.com> 1363718116 -0400
golang-hg 3cd53e993790dba37c0ee7fef471b5738fb33336

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