Odd function address in function instrumentation routines on ARM

["Lorenz, Daniel" <d dot lorenz at fz-juelich dot de>]

Hello,

I am working on performance analysis tools. For instrumenting applications we use the compiler instrumentation flags
-finstrument-functions. The inserted function calls to __cyg_profile_func_enter and __cyg_profile_func_exit normally provide a function
pointer. With libbfd we lookup debug information for this function using this address. This worked fine for many years on different machines,

Recently, I tried to port our code to an ARM architecture (dual Cortex A9 processor)
running Ubuntu. Here, I discovered that the function addresses that are passed to
__cyg_profile_func_enter and __cyg_profile_func_exit do not match the address of the function that we get from libbfd. Although the difference might be caused
by libbfd or in the way we interface libbfd, I am wondering that __cyg_profile_func_enter
and __cyg_profile_func_exit provide odd function addresses, even if I specify -falign-functions=4.

I appended a small test case that shows the addresses that we get from function instrumentation and from libbfd. The output on the ARM
system looks like this:

Function: foo, Address: 34960
Function: main, Address: 35008
In __cyg_profile_func_enter. Function address: 35009
In __cyg_profile_func_enter. Function address: 34961
in foo
In __cyg_profile_func_exit. Function address: 34961
In __cyg_profile_func_exit. Function address: 35009

I tested it on two different machines:
1. dual-core ARM Cortex-A9 Tegar2 SoC with gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5, and
2. Snowball – Cortex A9 board, Nova A9500 dual Cortex A9 with gcc (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1.
I performed several builds and test runs and it seems that the address difference is always 1.

Is the function adress passed to __cyg_profile_func_enter and __cyg_profile_func_exit intenionally odd on ARM,
even when specifing -falign-function=4?

Best Regards,
Daniel Lorenz

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