Re: partially initialized structures in C (3)
Hello Dave, thank you for your answers. Yes, the reason for my confusion was twofold: first, the documentation of IBM, which states that the remaining components of partially initialized automatic structures are not initialized, which is not conforming to the ANSI standard and is not what the compilers do and second, the fact, that the MVI, which sets the first byte of the remainder of the structure to zero and the MVC, which does the rest, are separated by some 40 instructions from each other, so I didn't see the MVC at first look (the function prologue is located between these instructions) But, thanks to the mailing list, I had some closer looks and found the MVCs in the end, which ended my confusion and the whole mess. And: thank you for your advertisement. I like your compiler, but I will not be able to convince my customer to try it - they are very IBM bound, in my opinion. Kind regards Bernd Thomas David Rivers schrieb: I'm pretty confident the IBM compiler follows the ANSI C standard and that some other reason is the cause of the confusion. If you discover it doesn't, and it's a problem; might I humbly offer our alternative (which can operate in your LE environment.) We definately would initialize that structure to all zeros. And, if you're recompiling anyway... might as well give our compiler a try... Just a (partially shameless) plug. - Dave Rivers - -- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
Re: partially initialized structures in C (3)
To David:
no, there is no MVC. This is the z/OS V1.6 C-Compiler.
I will try and examine the newer versions. Maybe the error is only in this
version. But the description in the language reference also tells that the
remaining components remain uninitialized, which is very strange.
We, too, do this initialization all the time. That's why we feel in
trouble now.
Most of the time, the areas are explicitly initalized later, anyway, so
there is no problem.
But in this case, it is not. But still, most of the time, the area is
zero, because it has not
been used before. So there is still no problem. We observed this problem
in the last week
for the first time and it took us several hours to find the reason for it.
To Charles:
The next component is not char, so it makes no sense to simply put
a single hex zero in front of it. The only good reason for the MVI would be
if a overlapped MVC would follow.
Kind regards
Bernd
David Crayford schrieb:
Are you sure there isn't an MVC after the MVI?
I rely on that kind of initialization all the time and have never had
a problem. A quick test program shows the correct behavior.
If this is not working as the ANSI standard I suggest you open a PMR.
To circumvent the problem compile with INITAUTO(0).
* *
struct F *
{ * int
a; * char
string[20];* short
s;*
};
* *struct F f =
{0}; LA r0,0
ST r0,f.F.a(,r4,2016) MVI
f(r4,2020),0 MVC f(23,r4,2021),f(r4,2020)
Compiled with CHECKOUT compiler option generates the following message.
INFORMATIONAL CCN3447 DOC.C(F1):14The member(s) starting from
string will be initialized with a default value of
0.
Bernd Oppolzer wrote:
Sorry for the missing line feeds.
C statement:
*scp1215ein in1215 = { 0 };
Pseudo ASSEMBLER (structure starts at 272(r13)):
STr6,a5:d272:l4(,r13,272)
MVI a5:d276:l1(r13,276),0
C statement:
*scp1215aus out1215= { 0 };
Pseudo ASSEMBLER (structure starts at 296(r13)):
STr6,a5:d296:l4(,r13,296)
MVI a5:d300:l1(r13,300),0
Kind regards
Bernd
Bernd Oppolzer schrieb:
To make it clear:
see above
The ST operations initialize the first components of the structures,
which are fullwords. This is what should be done, according to
the IBM C language reference.
The rest of the structures should remain unchanged (uninitialized),
according to IBM's language reference, and should be set to zero,
according to ANSI C language reference. The structure out1215,
for example, is 24 bytes long.
Now the MVI makes absolutely no sense to me.
It would only make some sense, if it was followed by an overlapped MVC
instruction, which would set the rest of the structure to zero. But
such a
instruction is not generated by the compiler.
???
Kind regards
Bernd
Bernd Oppolzer schrieb:
Hello all,
sorry for asking this question on IBM-Main, but the C370 list is so
silent
that I doubt that anyone is actually listening.
We observed a sort of problem today which showed up as a 0C4 abend
due to a not proper initialized pointer component of a C structure.
Further examination showed that the structured was initialized as
follows
structure_type structure_identified = { 0 };
The structure has several components; the last component is the
pointer.
According to the IBM C language reference, only the first component is
initialized to zero, and the other components have random contents,
because the storage class is automatic. The compiler generates only
initialization logic for the first few bytes of the auto structure.
So from this
point of view, everything is right.
But: the ANSI C language reference, for example in the Kernighan
Ritchie
book appendix, and most other C language references I found on the
web,
clearly state that if the number of initializers on structure
initialization is less
than the number of structure components, the remaining components are
initialized to zero, even for auto structures.
This is not an error in that sense that the compiler does not what
is written
in the language reference, but instead it is a contradiction
between IBM's
language reference and ANSI language reference.
What do you think about this? Does it make sense to complain at IBM
about it? We have hundreds of C programs in production use which use
this kind of initialization (maybe) and now we are afraid that we
need to
examine all these programs.
Kind regards
Bernd
--
For IBM-MAIN
Re: partially initialized structures in C (3)
Hello David,
which version of the compiler did generate the MVC instructions?
was this with or without the INITAUTO option?
We use the z/OS v1.6 version, and this version only generates the MVI,
not the MVCs.
We will not use INITAUTO due to serious performance degradation.
At the moment, management discusses the strategy to follow:
a) opening a PMR with IBM, and, if IBM agrees and changes their compilers,
recompiling all our C programs
b) accepting the behaviour of the IBM C compilers and examining
all our sources, changing all partial structure initializations to
memset and, again,
recompiling all our C programs
Kind regards
Bernd
David Crayford schrieb:
Are you sure there isn't an MVC after the MVI?
I rely on that kind of initialization all the time and have never had
a problem. A quick test program shows the correct behavior.
If this is not working as the ANSI standard I suggest you open a PMR.
To circumvent the problem compile with INITAUTO(0).
* *
struct F *
{ * int
a; * char
string[20];* short
s;*
};
* *struct F f =
{0}; LA r0,0
ST r0,f.F.a(,r4,2016) MVI
f(r4,2020),0 MVC f(23,r4,2021),f(r4,2020)
Compiled with CHECKOUT compiler option generates the following message.
INFORMATIONAL CCN3447 DOC.C(F1):14The member(s) starting from
string will be initialized with a default value of
0.
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Re: partially initialized structures in C (3)
Bernd,
I'm using z/OS V1.10 without INITAUTO. We've compiled our code all the
way back to OS/390 2.8 and I can't recall ever seeing
this problem. I'm sure it's a codegen bug, otherwise what is the point
of the MVI?
I wouldn't accept anything other than a fix from IBM. Although your
compiler is out of support!
Quote 6.7.8.21 of the ANSI C standard which clearly states:
If there are fewer initializers in a brace-enclosed list than there are
elements or members
of an aggregate, or fewer characters in a string literal used to
initialize an array of known
size than there are elements in the array, the remainder of the
aggregate shall be
initialized implicitly the same as objects that have static storage
duration.
Bernd Oppolzer wrote:
Hello David,
which version of the compiler did generate the MVC instructions?
was this with or without the INITAUTO option?
We use the z/OS v1.6 version, and this version only generates the MVI,
not the MVCs.
We will not use INITAUTO due to serious performance degradation.
At the moment, management discusses the strategy to follow:
a) opening a PMR with IBM, and, if IBM agrees and changes their
compilers,
recompiling all our C programs
b) accepting the behaviour of the IBM C compilers and examining
all our sources, changing all partial structure initializations to
memset and, again,
recompiling all our C programs
Kind regards
Bernd
David Crayford schrieb:
Are you sure there isn't an MVC after the MVI?
I rely on that kind of initialization all the time and have never had
a problem. A quick test program shows the correct behavior.
If this is not working as the ANSI standard I suggest you open a PMR.
To circumvent the problem compile with INITAUTO(0).
* *
struct F *
{ * int
a; * char
string[20];* short
s;*
};
* *struct F f =
{0}; LA r0,0
ST r0,f.F.a(,r4,2016) MVI
f(r4,2020),0 MVC f(23,r4,2021),f(r4,2020)
Compiled with CHECKOUT compiler option generates the following message.
INFORMATIONAL CCN3447 DOC.C(F1):14The member(s) starting from
string will be initialized with a default value of
0.
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Re: partially initialized structures in C (3)
Hi Bernd
We had several PMR's about the C++ compiler and the compiler team
reacted always
very fast and competently (maybe as they are in Canada ;-) )
On 5/19/2010 9:21 AM, Bernd Oppolzer wrote:
Hello David,
which version of the compiler did generate the MVC instructions?
was this with or without the INITAUTO option?
We use the z/OS v1.6 version, and this version only generates the MVI,
not the MVCs.
We will not use INITAUTO due to serious performance degradation.
At the moment, management discusses the strategy to follow:
a) opening a PMR with IBM, and, if IBM agrees and changes their
compilers,
recompiling all our C programs
b) accepting the behaviour of the IBM C compilers and examining
all our sources, changing all partial structure initializations to
memset and, again,
recompiling all our C programs
Kind regards
Bernd
David Crayford schrieb:
Are you sure there isn't an MVC after the MVI?
I rely on that kind of initialization all the time and have never had
a problem. A quick test program shows the correct behavior.
If this is not working as the ANSI standard I suggest you open a PMR.
To circumvent the problem compile with INITAUTO(0).
* *
struct F *
{ * int
a; * char
string[20];* short
s;*
};
* *struct F f =
{0}; LA r0,0
ST r0,f.F.a(,r4,2016) MVI
f(r4,2020),0 MVC f(23,r4,2021),f(r4,2020)
Compiled with CHECKOUT compiler option generates the following message.
INFORMATIONAL CCN3447 DOC.C(F1):14The member(s) starting from
string will be initialized with a default value of 0.
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Re: partially initialized structures in C (3)
Hi Again Bernd,
That psuedo-assembler appears to be initializing
a 5-bytes of storage. Are you sure the 'scp1215ein'
data type is 24 bytes? Can you show the
typedef for 'scp1215ein'?
Does there happen to be any packing going on?
Bitfields, etc...
- Dave Rivers -
Bernd Oppolzer wrote:
Sorry for the missing line feeds.
C statement:
*scp1215ein in1215 = { 0 };
Pseudo ASSEMBLER (structure starts at 272(r13)):
STr6,a5:d272:l4(,r13,272)
MVI a5:d276:l1(r13,276),0
C statement:
*scp1215aus out1215= { 0 };
Pseudo ASSEMBLER (structure starts at 296(r13)):
STr6,a5:d296:l4(,r13,296)
MVI a5:d300:l1(r13,300),0
Kind regards
Bernd
Bernd Oppolzer schrieb:
To make it clear:
see above
The ST operations initialize the first components of the structures,
which are fullwords. This is what should be done, according to
the IBM C language reference.
The rest of the structures should remain unchanged (uninitialized),
according to IBM's language reference, and should be set to zero,
according to ANSI C language reference. The structure out1215,
for example, is 24 bytes long.
Now the MVI makes absolutely no sense to me.
It would only make some sense, if it was followed by an overlapped MVC
instruction, which would set the rest of the structure to zero. But
such a
instruction is not generated by the compiler.
???
Kind regards
Bernd
Bernd Oppolzer schrieb:
Hello all,
sorry for asking this question on IBM-Main, but the C370 list is so
silent
that I doubt that anyone is actually listening.
We observed a sort of problem today which showed up as a 0C4 abend
due to a not proper initialized pointer component of a C structure.
Further examination showed that the structured was initialized as
follows
structure_type structure_identified = { 0 };
The structure has several components; the last component is the pointer.
According to the IBM C language reference, only the first component is
initialized to zero, and the other components have random contents,
because the storage class is automatic. The compiler generates only
initialization logic for the first few bytes of the auto structure.
So from this
point of view, everything is right.
But: the ANSI C language reference, for example in the Kernighan Ritchie
book appendix, and most other C language references I found on the web,
clearly state that if the number of initializers on structure
initialization is less
than the number of structure components, the remaining components are
initialized to zero, even for auto structures.
This is not an error in that sense that the compiler does not what is
written
in the language reference, but instead it is a contradiction between
IBM's
language reference and ANSI language reference.
What do you think about this? Does it make sense to complain at IBM
about it? We have hundreds of C programs in production use which use
this kind of initialization (maybe) and now we are afraid that we
need to
examine all these programs.
Kind regards
--
riv...@dignus.comWork: (919) 676-0847
Get your mainframe programming tools at http://www.dignus.com
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Re: partially initialized structures in C (3)
Bernd Oppolzer wrote: Hello David, which version of the compiler did generate the MVC instructions? was this with or without the INITAUTO option? We use the z/OS v1.6 version, and this version only generates the MVI, not the MVCs. We will not use INITAUTO due to serious performance degradation. At the moment, management discusses the strategy to follow: a) opening a PMR with IBM, and, if IBM agrees and changes their compilers, recompiling all our C programs b) accepting the behaviour of the IBM C compilers and examining all our sources, changing all partial structure initializations to memset and, again, recompiling all our C programs I'm pretty confident the IBM compiler follows the ANSI C standard and that some other reason is the cause of the confusion. If you discover it doesn't, and it's a problem; might I humbly offer our alternative (which can operate in your LE environment.) We definately would initialize that structure to all zeros. And, if you're recompiling anyway... might as well give our compiler a try... Just a (partially shameless) plug. - Dave Rivers - -- riv...@dignus.comWork: (919) 676-0847 Get your mainframe programming tools at http://www.dignus.com -- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
Re: partially initialized structures in C (3)
-Original Message-
From: IBM Mainframe Discussion List
[mailto:ibm-m...@bama.ua.edu] On Behalf Of Bernd Oppolzer
Sent: Tuesday, May 18, 2010 2:14 PM
To: IBM-MAIN@bama.ua.edu
Subject: partially initialized structures in C (3)
Sorry for the missing line feeds.
C statement:
*scp1215ein in1215 = { 0 };
Pseudo ASSEMBLER (structure starts at 272(r13)):
STr6,a5:d272:l4(,r13,272)
MVI a5:d276:l1(r13,276),0
C statement:
*scp1215aus out1215= { 0 };
Pseudo ASSEMBLER (structure starts at 296(r13)):
STr6,a5:d296:l4(,r13,296)
MVI a5:d300:l1(r13,300),0
Kind regards
Bernd
Just me (and I'm not really good with C), but why not just use memset()?
memset(in1215,0,sizeof in1215);
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Re: partially initialized structures in C (3)
Are you sure there isn't an MVC after the MVI?
I rely on that kind of initialization all the time and have never had a
problem. A quick test program shows the correct behavior.
If this is not working as the ANSI standard I suggest you open a PMR. To
circumvent the problem compile with INITAUTO(0).
*
*struct F
*{
* int a;
* char string[20];
* short s;
*};
*
*struct F f = {0};
LA r0,0
ST r0,f.F.a(,r4,2016)
MVI f(r4,2020),0
MVC f(23,r4,2021),f(r4,2020)
Compiled with CHECKOUT compiler option generates the following message.
INFORMATIONAL CCN3447 DOC.C(F1):14The member(s) starting from
string will be initialized with a default value of
0.
Bernd Oppolzer wrote:
Sorry for the missing line feeds.
C statement:
*scp1215ein in1215 = { 0 };
Pseudo ASSEMBLER (structure starts at 272(r13)):
STr6,a5:d272:l4(,r13,272)
MVI a5:d276:l1(r13,276),0
C statement:
*scp1215aus out1215= { 0 };
Pseudo ASSEMBLER (structure starts at 296(r13)):
STr6,a5:d296:l4(,r13,296)
MVI a5:d300:l1(r13,300),0
Kind regards
Bernd
Bernd Oppolzer schrieb:
To make it clear:
see above
The ST operations initialize the first components of the structures,
which are fullwords. This is what should be done, according to
the IBM C language reference.
The rest of the structures should remain unchanged (uninitialized),
according to IBM's language reference, and should be set to zero,
according to ANSI C language reference. The structure out1215,
for example, is 24 bytes long.
Now the MVI makes absolutely no sense to me.
It would only make some sense, if it was followed by an overlapped MVC
instruction, which would set the rest of the structure to zero. But
such a
instruction is not generated by the compiler.
???
Kind regards
Bernd
Bernd Oppolzer schrieb:
Hello all,
sorry for asking this question on IBM-Main, but the C370 list is so
silent
that I doubt that anyone is actually listening.
We observed a sort of problem today which showed up as a 0C4 abend
due to a not proper initialized pointer component of a C structure.
Further examination showed that the structured was initialized as
follows
structure_type structure_identified = { 0 };
The structure has several components; the last component is the
pointer.
According to the IBM C language reference, only the first component is
initialized to zero, and the other components have random contents,
because the storage class is automatic. The compiler generates only
initialization logic for the first few bytes of the auto structure.
So from this
point of view, everything is right.
But: the ANSI C language reference, for example in the Kernighan
Ritchie
book appendix, and most other C language references I found on the web,
clearly state that if the number of initializers on structure
initialization is less
than the number of structure components, the remaining components are
initialized to zero, even for auto structures.
This is not an error in that sense that the compiler does not what
is written
in the language reference, but instead it is a contradiction between
IBM's
language reference and ANSI language reference.
What do you think about this? Does it make sense to complain at IBM
about it? We have hundreds of C programs in production use which use
this kind of initialization (maybe) and now we are afraid that we
need to
examine all these programs.
Kind regards
Bernd
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Re: partially initialized structures in C (3)
Now the MVI makes absolutely no sense to me.
It makes the string initialized to the null string (), no?
Charles
-Original Message-
From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf
Of Bernd Oppolzer
Sent: Tuesday, May 18, 2010 12:14 PM
To: IBM-MAIN@bama.ua.edu
Subject: partially initialized structures in C (3)
Sorry for the missing line feeds.
C statement:
*scp1215ein in1215 = { 0 };
Pseudo ASSEMBLER (structure starts at 272(r13)):
STr6,a5:d272:l4(,r13,272)
MVI a5:d276:l1(r13,276),0
C statement:
*scp1215aus out1215= { 0 };
Pseudo ASSEMBLER (structure starts at 296(r13)):
STr6,a5:d296:l4(,r13,296)
MVI a5:d300:l1(r13,300),0
Kind regards
Bernd
Bernd Oppolzer schrieb:
To make it clear:
see above
The ST operations initialize the first components of the structures,
which are fullwords. This is what should be done, according to
the IBM C language reference.
The rest of the structures should remain unchanged (uninitialized),
according to IBM's language reference, and should be set to zero,
according to ANSI C language reference. The structure out1215,
for example, is 24 bytes long.
Now the MVI makes absolutely no sense to me.
It would only make some sense, if it was followed by an overlapped MVC
instruction, which would set the rest of the structure to zero. But
such a
instruction is not generated by the compiler.
???
Kind regards
Bernd
Bernd Oppolzer schrieb:
Hello all,
sorry for asking this question on IBM-Main, but the C370 list is so
silent
that I doubt that anyone is actually listening.
We observed a sort of problem today which showed up as a 0C4 abend
due to a not proper initialized pointer component of a C structure.
Further examination showed that the structured was initialized as
follows
structure_type structure_identified = { 0 };
The structure has several components; the last component is the pointer.
According to the IBM C language reference, only the first component is
initialized to zero, and the other components have random contents,
because the storage class is automatic. The compiler generates only
initialization logic for the first few bytes of the auto structure.
So from this
point of view, everything is right.
But: the ANSI C language reference, for example in the Kernighan Ritchie
book appendix, and most other C language references I found on the web,
clearly state that if the number of initializers on structure
initialization is less
than the number of structure components, the remaining components are
initialized to zero, even for auto structures.
This is not an error in that sense that the compiler does not what is
written
in the language reference, but instead it is a contradiction between
IBM's
language reference and ANSI language reference.
What do you think about this? Does it make sense to complain at IBM
about it? We have hundreds of C programs in production use which use
this kind of initialization (maybe) and now we are afraid that we
need to
examine all these programs.
Kind regards
Bernd
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