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Strange ARM issue: wrong exception table type?

david.hagood@gmail.com david.hagood@gmail.com
Wed Feb 1 16:40:00 GMT 2012 
I am having a strange issue with cross-compiling ARM programs. When I
build a C++ executable that throws exceptions, they don't work: no catch()
statements work, and all throw operations go straight to std::terminate().
My co-workers, who are using in theory the exact same tool chain, don't
see this (and I've checked the md5sum of their tools vs. mine and they
seem to match).

I've traced it down to the assembler: I can have them compile the C++ file
to a .s, and just assemble and link it, and it breaks. If they send me a
.o and I link that, it works. The assembler files they send me are the
same as the ones my compiler generates (verified via diff), but the
objects they produce vs. the objects I produce are different.

I've traced the point of difference to the .ARM.extab and .ARM.exidx
sections:

Contents of section .ARM.extab:
- 0000 00000080 84429b01 b0b0b083 ff002501  .....B........%.
+ 0000 00000000 84429b01 b0b0b083 ff002501  .....B........%.
  0010 1b1c9001 ac0101c0 01040000 dc013cac  ..............<.

Contents of section .ARM.exidx:
- 0000 00000080 00000080 7c010080 34000080  ........|...4...
- 0010 e0010080 40000080                    ....@...
+ 0000 00000000 00000000 7c010000 34000000  ........|...4...
+ 0010 e0010000 40000000                    ....@...

If I read the ARM EABI spec correctly, the difference is that my assembler
is generating the ARM Compact form (bit 31 set), and theirs are generating
the standard form. I assume that's preventing the run time library from
finding the catch() blocks.

What would cause my "as" to generate a different output than theirs for
the same input file? (and I've verified the MD5 of my "as" and theirs
match). And how can I fix this?
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