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From: John Reagan <johnrreagan@earthlink.net>
Newsgroups: comp.os.vms
Subject: Re: New VSI blog post
Date: Wed, 31 Jul 2024 16:44:04 -0400
Organization: i2pn2 (i2pn.org)
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On 7/30/2024 7:59 PM, Arne Vajhøj wrote:
> On 7/30/2024 8:25 AM, Simon Clubley wrote:
>> On 2024-07-29, John Reagan <johnrreagan@earthlink.net> wrote:
>>> Other
>>> than bugs in the compilers and OS, the most common issue I've seen is a
>>> mismatch of 32/64 bit variables.  I've seen 20 or so instance of code
>>> that is doing a 64-bit write into a 32-bit variable.
>> [snip]
>>> It mostly has been in BLISS and C code.
>>
>> I don't know enough about BLISS to make a judgement about how bad the
>> code that does this is,
> 
> I don't think Bliss is the right language for 100% type safe code.
> 
> :-)
> 
>>                         but I would be very interested to see the C code
>> that makes this possible.
>>
>> Without an obviously incorrect explicit type conversion (which is a 
>> serious
>> bug in the user's C code), I am not seeing how this is possible under C
>> as the compiler should generate the appropriate size-conversion code
>> automatically if you assign from a 64-bit variable into a 32-bit 
>> variable.
> 
> I have no idea what examples John is seeing, but it is not that
> hard to come up with examples.
> 
> Ignoring warnings:
> 
> $ type warns.h
> #include <stdint.h>
> 
> void something(int64_t *v);
> $ type warns.c
> #include <stdint.h>
> 
> #include "warns.h"
> 
> void something(int64_t *v)
> {
>      *v = -1;
> }
> 
> $ type warnm.c
> #include <stdio.h>
> #include <stdint.h>
> 
> #include "warns.h"
> 
> int main()
> {
>      int32_t v[3] = { 0, 0, 0 };
>      something(&v[1]);
>      printf("%ld %ld %ld\n", v[0], v[1], v[2]);
>      return 0;
> }
> 
> $ cc warns
> $ cc warnm
> 
>      something(&v[1]);
> ..............^
> %CC-W-PTRMISMATCH, In this statement, the referenced type of the pointer 
> value "&v[1]" is "int", which is not compatible with "long
> long".
> at line number 9 in file DKA0:[arne.bits]warnm.c;1
> $ link/exe=warn warnm + warns
> %ILINK-W-COMPWARN, compilation warnings
>          module: WARNM
>          file: DKA0:[arne.bits]warnm.OBJ;2
> $ run warn
> 0 -1 -1
> 
> Having an inconsistent declaration and forget to
> include .h in implementing .c file:
> 
> $ type nowarns.h
> #include <stdint.h>
> 
> void something(int32_t *v);
> $ type nowarns.c
> #include <stdint.h>
> 
> //#include "nowarns.h"
> 
> void something(int64_t *v)
> {
>      *v = -1;
> }
> 
> $ type nowarnm.c
> #include <stdio.h>
> #include <stdint.h>
> 
> #include "nowarns.h"
> 
> int main()
> {
>      int32_t v[3] = { 0, 0, 0 };
>      something(&v[1]);
>      printf("%ld %ld %ld\n", v[0], v[1], v[2]);
>      return 0;
> }
> 
> $ cc nowarns
> $ cc nowarnm
> $ link/exe=nowarn nowarnm + nowarns
> $ run nowarn
> 0 -1 -1
> 
> Having an inconsistency and use old style function
> declaration without arguments:
> 
> $ type badolds.h
> void something();
> $ type badolds.c
> #include <stdint.h>
> 
> #include "badolds.h"
> 
> void something(int64_t *v)
> {
>      *v = -1;
> }
> 
> $ type badoldm.c
> #include <stdio.h>
> #include <stdint.h>
> 
> #include "badolds.h"
> 
> int main()
> {
>      int32_t v[3] = { 0, 0, 0 };
>      something(&v[1]);
>      printf("%ld %ld %ld\n", v[0], v[1], v[2]);
>      return 0;
> }
> 
> $ cc badolds
> $ cc badoldm
> $ link/exe=badold badoldm + badolds
> $ run badold
> 0 -1 -1
> 
> Mixing VMS C and Clang C without consideration:
> 
> $ type trickys.h
> void something(long *v);
> $ type trickys.c
> #include "trickys.h"
> 
> void something(long *v)
> {
>      *v = -1;
> }
> 
> $ type trickym.c
> #include <stdio.h>
> 
> #include "trickys.h"
> 
> int main()
> {
>      long v[3] = { 0, 0, 0 };
>      something(&v[1]);
>      printf("%ld %ld %ld\n", v[0], v[1], v[2]);
>      return 0;
> }
> $ clang trickys.c
> $ cc/name=as_is trickym
> $ link/exe=tricky trickym + trickys
> $ run tricky
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