GNU LD fails to generate correct ARM Thumb veneer

good day people:

i have been using GNUARM/Cygwin for some time now and i have not
encountered a problem like this before.

BACKGROUND
- target MCU is STR71x
- CPU core is ARM7TDMI
- toolchain is GNUARM 4.1.1 on Cygwin
- source code
  - the first file to be linked is an ARM assembly .s file
    that contains the ARM vector table and handler addresses.
    the vector table is in a separate section called .VhaInit.
    when linked, it is located to 0x20000000 (SRAM) or
    0x40000000 (Flash)

  - the second file is another ARM assembly .s file that contains
    C startup code. when linked, the .text is located to 0x20000080
    (SRAM) or 0x40000080 (Flash), just after .VhaInit.

  - assembly files are assembled with -mthumb-interworking but are
    written in pure ARM code.

  - there is a C file that is compiled with -mthumb
    -mthumb-interworking.

  - i also link with -gc-sections, and C code is compiled with
    -ffunction-sections and -fdata-sections so that unused C code is
    eliminated by the linker.

  - ResetHandler entry is set to 0x400C0000 using --defsym option of
    LD: --defsym ResetHandler=0x400C0000

PROBLEM
- when i add code to access .VhaInit entries from .text to prevent the
  garbage collection of .VhaInit, Thumb Interworking code is ZERO. the
  entries are present, but no interworking code is present.

- when i remove code that accesses .VhaInit, Interworking code is
  correct.

- when i disable -ffunction-sections, -fdata-sections, and
  -gc-sections, and when i still access data in .VhaInit from .text,
  Interworking is correct.

so, what's going on? 8-)

i think its a bug in GNU LD.

any help will be gratefully accepted.

have a nice day,

Aaron
-- 
{tel: +91-20-6526-7076; cell: +91-9970-591-079; fax: +1-800-450-5419}

adsouzp wrote:
...
> - when i add code to access .VhaInit entries from .text to prevent the
>   garbage collection of .VhaInit, Thumb Interworking code is ZERO. the
>   entries are present, but no interworking code is present.
...
It is not analysis of your problem but maybe it will help a little.
There is a special directive KEEP to prevent section removal by linker.
Below fargment of my rom71x.ld linker file (for RAM placement KEEP works as well).

	.text :
	{
		KEEP(*(.vectrom))
		KEEP(*(.init))
		*(.text .text.*)
		*(.gnu.linkonce.t.*)
		*(.glue_7t .glue_7)
		KEEP(*(.fini))
		*(.gcc_except_table)
	} >CODE =0
	. = ALIGN(4);

Regards,
-- 
Artur Lipowski

hello:

>It is not analysis of your problem but maybe it will help a little.

thank you, thank you.

i did a lot of research on the problem and filed bugs in GCC bugzilla
as well as on Mikrocontroller.net.

pls see these links for more information:
- GCC Bugzilla Bug 6726
  http://sourceware.org/bugzilla/show_bug.cgi?id=6726

- GCC Bugzilla Bug 6727
  http://sourceware.org/bugzilla/show_bug.cgi?id=6727

- Mikrocontroller.net Forum
  http://en.mikrocontroller.net/topic/158791#699646

GLOBAL CONDITIONS
if:
- you enable --gc-sections
- you enable Thumb Interworking

PROBLEM 1
- if you do not define program entry point: you get the ldlang.c 4275 
error

SOLUTION 1
- simply define entry point _start or whatever using --entry if required

PROBLEM
- you position another section using --section-start before .text using 
-Ttext
: you get ZERO interworking code

SOLUTION
- position .data/other section AFTER .text. place -Ttext before 
--section-start
  or -Tdata.

i hope that this is helpful to you.

Aaron

hello:

here is an update on the bugs that i encountered.

Nick Clifton of RedHat says that both bugs are old,
known ones and have been fixed in the latest version
of binutils.

pls see bug 6726 & 6727 bug reports for updates.

- GCC Bugzilla Bug 6726
  http://sourceware.org/bugzilla/show_bug.cgi?id=6726

- GCC Bugzilla Bug 6727
  http://sourceware.org/bugzilla/show_bug.cgi?id=6727

Aaron
--
{ why discuss/expose needlessly and start a commotion? }

hello:

here is an update on the bugs that i encountered.

Nick Clifton of RedHat says that both bugs are old,
known ones and have been fixed in the latest version
of binutils.

pls see bug 6726 & 6727 bug reports for updates.

- GCC Bugzilla Bug 6726
  http://sourceware.org/bugzilla/show_bug.cgi?id=6726

- GCC Bugzilla Bug 6727
  http://sourceware.org/bugzilla/show_bug.cgi?id=6727

Aaron
--
{ why discuss/expose needlessly and start a commotion? }