This is the mail archive of the mailing list for the crossgcc project.

See the CrossGCC FAQ for lots more information.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

arm-elf-gcc : change default data alignement depending on ARM/THUMB

Dear all,

I am trying to figure out why gcc always aligns on 4 bytes boundaries (32 bits) on arm-elf-gcc in an attempt to reduce code footprint. I found that GCC produces much bigger code than ADS (30 to 50 %) when ARM and THUMB are mixed (interworking enabled) on our project.

It indeed seems that ARM ADS 1.2 aligns on halfwords (16 bits) when in THUMB mode (along with much more sophisticated rules). GCC different behavior causes much more padding to be inserted in structs members and, as the project I work on uses HW mapped registers, application crashes.
For now, I worked around that using a compile time define to enable the __attribute((packed))__ on the struct(s). I would nevertheless like to know whether there is another solution.

I am also digging into the arm.h and arm.c files (thanks to the gcc's internal manual) to try to change the alignment behavior.

Could you give me other ideas/solutions on that point?

Thanks for your consideration,


------ Want more information? See the CrossGCC FAQ, Want to unsubscribe? Send a note to

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]