Hello,
I'm trying a fat16 library that use an union for storing the
bootsector data, and it seems the compiler doesn't handle correctly
the width of types in memory.
So I searched some help on crossworks (gcc) compiler and found that I
have to use this attribute with my concerned unions :
__attribute__ ((__packed__))
But if the compiler doesn't shout at me when compiling , it seems it
has no effect : my union is badly aligned.
Have any idea ?
Struct/Union alignement problem with Crossworks
Started by ●September 20, 2005
Reply by ●September 20, 20052005-09-20
If you have a union of two (or more) structures, those structures must
also have a packed attribute.
--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
CrossWorks for MSP430, ARM, AVR and now MAXQ processors
> -----Original Message-----
> From: nourson54 [mailto:nourson54@nour...]
> Sent: 20 September 2005 14:54
> To: lpc2000@lpc2...
> Subject: [lpc2000] Struct/Union alignement problem with Crossworks
>
> Hello,
>
> I'm trying a fat16 library that use an union for storing the
> bootsector data, and it seems the compiler doesn't handle
> correctly the width of types in memory.
> So I searched some help on crossworks (gcc) compiler and
> found that I have to use this attribute with my concerned unions :
> __attribute__ ((__packed__))
>
> But if the compiler doesn't shout at me when compiling , it
> seems it has no effect : my union is badly aligned.
>
> Have any idea ? > ------------------------ Yahoo! Groups Sponsor
> --------------------~--> Fair play? Video games influencing
> politics. Click and talk back!
> http://us.click.yahoo.com/T8sf5C/tzNLAA/TtwFAA/dN_tlB/TM
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> ------~- > Yahoo! Groups Links
also have a packed attribute.
--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
CrossWorks for MSP430, ARM, AVR and now MAXQ processors
> -----Original Message-----
> From: nourson54 [mailto:nourson54@nour...]
> Sent: 20 September 2005 14:54
> To: lpc2000@lpc2...
> Subject: [lpc2000] Struct/Union alignement problem with Crossworks
>
> Hello,
>
> I'm trying a fat16 library that use an union for storing the
> bootsector data, and it seems the compiler doesn't handle
> correctly the width of types in memory.
> So I searched some help on crossworks (gcc) compiler and
> found that I have to use this attribute with my concerned unions :
> __attribute__ ((__packed__))
>
> But if the compiler doesn't shout at me when compiling , it
> seems it has no effect : my union is badly aligned.
>
> Have any idea ? > ------------------------ Yahoo! Groups Sponsor
> --------------------~--> Fair play? Video games influencing
> politics. Click and talk back!
> http://us.click.yahoo.com/T8sf5C/tzNLAA/TtwFAA/dN_tlB/TM
> --------------------------
> ------~- > Yahoo! Groups Links
Reply by ●September 20, 20052005-09-20
In a similar situation I use:
#pragma pack (2)
...
Structures, etc
#pragma pack ()
and this work (align at word boundaries)
Regards
Angel Sanchez --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> Hello,
>
> I'm trying a fat16 library that use an union for storing the
> bootsector data, and it seems the compiler doesn't handle correctly
> the width of types in memory.
> So I searched some help on crossworks (gcc) compiler and found that
I
> have to use this attribute with my concerned unions :
> __attribute__ ((__packed__))
>
> But if the compiler doesn't shout at me when compiling , it seems it
> has no effect : my union is badly aligned.
>
> Have any idea ?
#pragma pack (2)
...
Structures, etc
#pragma pack ()
and this work (align at word boundaries)
Regards
Angel Sanchez --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> Hello,
>
> I'm trying a fat16 library that use an union for storing the
> bootsector data, and it seems the compiler doesn't handle correctly
> the width of types in memory.
> So I searched some help on crossworks (gcc) compiler and found that
I
> have to use this attribute with my concerned unions :
> __attribute__ ((__packed__))
>
> But if the compiler doesn't shout at me when compiling , it seems it
> has no effect : my union is badly aligned.
>
> Have any idea ?
Reply by ●September 20, 20052005-09-20
I tried to set the attibute on all structs/unions but at compiling
time , gcc told : "`__packed__' attribute ignored" for each attribute ... --- In lpc2000@lpc2..., "Paul Curtis" <plc@r...> wrote:
> If you have a union of two (or more) structures, those structures must
> also have a packed attribute.
>
> --
> Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
> CrossWorks for MSP430, ARM, AVR and now MAXQ processors
>
> > -----Original Message-----
> > From: nourson54 [mailto:nourson54@y...]
> > Sent: 20 September 2005 14:54
> > To: lpc2000@lpc2...
> > Subject: [lpc2000] Struct/Union alignement problem with Crossworks
> >
> > Hello,
> >
> > I'm trying a fat16 library that use an union for storing the
> > bootsector data, and it seems the compiler doesn't handle
> > correctly the width of types in memory.
> > So I searched some help on crossworks (gcc) compiler and
> > found that I have to use this attribute with my concerned unions :
> > __attribute__ ((__packed__))
> >
> > But if the compiler doesn't shout at me when compiling , it
> > seems it has no effect : my union is badly aligned.
> >
> > Have any idea ?
> >
> >
> >
> >
> >
> > ------------------------ Yahoo! Groups Sponsor
> > --------------------~--> Fair play? Video games influencing
> > politics. Click and talk back!
> > http://us.click.yahoo.com/T8sf5C/tzNLAA/TtwFAA/dN_tlB/TM
> > --------------------------
> > ------~->
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
time , gcc told : "`__packed__' attribute ignored" for each attribute ... --- In lpc2000@lpc2..., "Paul Curtis" <plc@r...> wrote:
> If you have a union of two (or more) structures, those structures must
> also have a packed attribute.
>
> --
> Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
> CrossWorks for MSP430, ARM, AVR and now MAXQ processors
>
> > -----Original Message-----
> > From: nourson54 [mailto:nourson54@y...]
> > Sent: 20 September 2005 14:54
> > To: lpc2000@lpc2...
> > Subject: [lpc2000] Struct/Union alignement problem with Crossworks
> >
> > Hello,
> >
> > I'm trying a fat16 library that use an union for storing the
> > bootsector data, and it seems the compiler doesn't handle
> > correctly the width of types in memory.
> > So I searched some help on crossworks (gcc) compiler and
> > found that I have to use this attribute with my concerned unions :
> > __attribute__ ((__packed__))
> >
> > But if the compiler doesn't shout at me when compiling , it
> > seems it has no effect : my union is badly aligned.
> >
> > Have any idea ?
> >
> >
> >
> >
> >
> > ------------------------ Yahoo! Groups Sponsor
> > --------------------~--> Fair play? Video games influencing
> > politics. Click and talk back!
> > http://us.click.yahoo.com/T8sf5C/tzNLAA/TtwFAA/dN_tlB/TM
> > --------------------------
> > ------~->
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
Reply by ●September 20, 20052005-09-20
here's a part of code :
typedef struct
{
uint8_t bsjmpBoot[3];
char bsOEMName[8];
uint16_t bsBytesPerSec;
...
}BootSector;
and a buffer FAT16_buffer[512] where I put data frome SD card in.
for example , if I declare a Bootsector struct at same address of
FAT16_Buffer, and read the first sector of my SDcard, I coul read
directly the field of my struct.
bsjmpBoot is 3 bytes and is OK
BsOEMName is 8 bytes and OK
bsByteBytesPerSec is 2 bytes is not OK because bsOEMBoot+bsOEMName =
11 bytes : 1 bytes is 'filled' between bsOEMName and bsBytesPerSec.
So data becomes buggy. with the #pramga pack (x) , Can I 'byte align' each field of my struct ?
--- In lpc2000@lpc2..., "Angel Sanchez" <angelsp@a...> wrote:
> In a similar situation I use:
>
> #pragma pack (2)
>
> ...
> Structures, etc
>
> #pragma pack ()
>
> and this work (align at word boundaries)
>
> Regards
> Angel Sanchez > --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> > Hello,
> >
> > I'm trying a fat16 library that use an union for storing the
> > bootsector data, and it seems the compiler doesn't handle correctly
> > the width of types in memory.
> > So I searched some help on crossworks (gcc) compiler and found that
> I
> > have to use this attribute with my concerned unions :
> > __attribute__ ((__packed__))
> >
> > But if the compiler doesn't shout at me when compiling , it seems it
> > has no effect : my union is badly aligned.
> >
> > Have any idea ?
typedef struct
{
uint8_t bsjmpBoot[3];
char bsOEMName[8];
uint16_t bsBytesPerSec;
...
}BootSector;
and a buffer FAT16_buffer[512] where I put data frome SD card in.
for example , if I declare a Bootsector struct at same address of
FAT16_Buffer, and read the first sector of my SDcard, I coul read
directly the field of my struct.
bsjmpBoot is 3 bytes and is OK
BsOEMName is 8 bytes and OK
bsByteBytesPerSec is 2 bytes is not OK because bsOEMBoot+bsOEMName =
11 bytes : 1 bytes is 'filled' between bsOEMName and bsBytesPerSec.
So data becomes buggy. with the #pramga pack (x) , Can I 'byte align' each field of my struct ?
--- In lpc2000@lpc2..., "Angel Sanchez" <angelsp@a...> wrote:
> In a similar situation I use:
>
> #pragma pack (2)
>
> ...
> Structures, etc
>
> #pragma pack ()
>
> and this work (align at word boundaries)
>
> Regards
> Angel Sanchez > --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> > Hello,
> >
> > I'm trying a fat16 library that use an union for storing the
> > bootsector data, and it seems the compiler doesn't handle correctly
> > the width of types in memory.
> > So I searched some help on crossworks (gcc) compiler and found that
> I
> > have to use this attribute with my concerned unions :
> > __attribute__ ((__packed__))
> >
> > But if the compiler doesn't shout at me when compiling , it seems it
> > has no effect : my union is badly aligned.
> >
> > Have any idea ?
Reply by ●September 20, 20052005-09-20
You would need:
typedef struct
{
uint8_t bsjmpBoot[3];
char bsOEMName[8];
uint16_t bsBytesPerSec;
...
} __attribute__((packed)) BootSector;
Given...
BootSector bs;
...then...
BS.bsBytesPerSec = 1
...generates...
BS.bsBytesPerSec = 1;
E59F200C ldr r2, [pc, #12]
E3843001 orr r3, r4, #0x00000001
E5C2300B strb r3, [r2, #11]
E5C2400C strb r4, [r2, #12]
So, bsBytesPerSec is accessed as bytes at offsets 11 and 12, which is
just what you wanted, isn't it?
--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
CrossWorks for MSP430, ARM, AVR and now MAXQ processors
> -----Original Message-----
> From: nourson54 [mailto:nourson54@nour...]
> Sent: 20 September 2005 16:31
> To: lpc2000@lpc2...
> Subject: [lpc2000] Re: Struct/Union alignement problem with Crossworks
>
> here's a part of code :
> typedef struct
> {
> uint8_t bsjmpBoot[3];
> char bsOEMName[8];
> uint16_t bsBytesPerSec;
> ...
> }BootSector;
>
> and a buffer FAT16_buffer[512] where I put data frome SD card in.
>
> for example , if I declare a Bootsector struct at same
> address of FAT16_Buffer, and read the first sector of my
> SDcard, I coul read directly the field of my struct.
>
> bsjmpBoot is 3 bytes and is OK
> BsOEMName is 8 bytes and OK
> bsByteBytesPerSec is 2 bytes is not OK because bsOEMBoot+bsOEMName =
> 11 bytes : 1 bytes is 'filled' between bsOEMName and bsBytesPerSec.
> So data becomes buggy. > with the #pramga pack (x) , Can I 'byte align' each field of
> my struct ? >
> --- In lpc2000@lpc2..., "Angel Sanchez" <angelsp@a...> wrote:
> > In a similar situation I use:
> >
> > #pragma pack (2)
> >
> > ...
> > Structures, etc
> >
> > #pragma pack ()
> >
> > and this work (align at word boundaries)
> >
> > Regards
> > Angel Sanchez
> >
> >
> > --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> > > Hello,
> > >
> > > I'm trying a fat16 library that use an union for storing the
> > > bootsector data, and it seems the compiler doesn't handle
> correctly
> > > the width of types in memory.
> > > So I searched some help on crossworks (gcc) compiler and
> found that
> > I
> > > have to use this attribute with my concerned unions :
> > > __attribute__ ((__packed__))
> > >
> > > But if the compiler doesn't shout at me when compiling ,
> it seems it
> > > has no effect : my union is badly aligned.
> > >
> > > Have any idea ? >
>
> ------------------------ Yahoo! Groups Sponsor
> --------------------~--> Most low income households are not
> online. Help bridge the digital divide today!
> http://us.click.yahoo.com/cd_AJB/QnQLAA/TtwFAA/dN_tlB/TM
> --------------------------
> ------~- > Yahoo! Groups Links
typedef struct
{
uint8_t bsjmpBoot[3];
char bsOEMName[8];
uint16_t bsBytesPerSec;
...
} __attribute__((packed)) BootSector;
Given...
BootSector bs;
...then...
BS.bsBytesPerSec = 1
...generates...
BS.bsBytesPerSec = 1;
E59F200C ldr r2, [pc, #12]
E3843001 orr r3, r4, #0x00000001
E5C2300B strb r3, [r2, #11]
E5C2400C strb r4, [r2, #12]
So, bsBytesPerSec is accessed as bytes at offsets 11 and 12, which is
just what you wanted, isn't it?
--
Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk
CrossWorks for MSP430, ARM, AVR and now MAXQ processors
> -----Original Message-----
> From: nourson54 [mailto:nourson54@nour...]
> Sent: 20 September 2005 16:31
> To: lpc2000@lpc2...
> Subject: [lpc2000] Re: Struct/Union alignement problem with Crossworks
>
> here's a part of code :
> typedef struct
> {
> uint8_t bsjmpBoot[3];
> char bsOEMName[8];
> uint16_t bsBytesPerSec;
> ...
> }BootSector;
>
> and a buffer FAT16_buffer[512] where I put data frome SD card in.
>
> for example , if I declare a Bootsector struct at same
> address of FAT16_Buffer, and read the first sector of my
> SDcard, I coul read directly the field of my struct.
>
> bsjmpBoot is 3 bytes and is OK
> BsOEMName is 8 bytes and OK
> bsByteBytesPerSec is 2 bytes is not OK because bsOEMBoot+bsOEMName =
> 11 bytes : 1 bytes is 'filled' between bsOEMName and bsBytesPerSec.
> So data becomes buggy. > with the #pramga pack (x) , Can I 'byte align' each field of
> my struct ? >
> --- In lpc2000@lpc2..., "Angel Sanchez" <angelsp@a...> wrote:
> > In a similar situation I use:
> >
> > #pragma pack (2)
> >
> > ...
> > Structures, etc
> >
> > #pragma pack ()
> >
> > and this work (align at word boundaries)
> >
> > Regards
> > Angel Sanchez
> >
> >
> > --- In lpc2000@lpc2..., "nourson54" <nourson54@y...> wrote:
> > > Hello,
> > >
> > > I'm trying a fat16 library that use an union for storing the
> > > bootsector data, and it seems the compiler doesn't handle
> correctly
> > > the width of types in memory.
> > > So I searched some help on crossworks (gcc) compiler and
> found that
> > I
> > > have to use this attribute with my concerned unions :
> > > __attribute__ ((__packed__))
> > >
> > > But if the compiler doesn't shout at me when compiling ,
> it seems it
> > > has no effect : my union is badly aligned.
> > >
> > > Have any idea ? >
>
> ------------------------ Yahoo! Groups Sponsor
> --------------------~--> Most low income households are not
> online. Help bridge the digital divide today!
> http://us.click.yahoo.com/cd_AJB/QnQLAA/TtwFAA/dN_tlB/TM
> --------------------------
> ------~- > Yahoo! Groups Links
