On Tue, Dec 1, 2015 at 1:24 AM, Barry Song <21cnbao@gmail.com> wrote:

hi guys,
sorry maybe my question is stupid as i am not a toolchain guy.

i have no idea why ld.so search so many paths. for example, put
"-rpath" with /home/cnb1szh/test in a simple test program. then during
dynamic linking at runtime, we get the below linking debug
information:

30693: find library=libmytest.so [0]; searching

30693: search path=/home/cnb1szh/test/tls/v7l/neon/vfp:/home/cnb1szh/test/tls/v7l/neon:/home/cnb1szh/test/tls/v7l/vfp:/home/cnb1szh/test/tls/v7l:/home/cnb1szh/test/tls/neon/vfp:/home/cnb1szh/test/tls/neon:/home/cnb1szh/test/tls/vfp:/home/cnb1szh/test/tls:/home/cnb1szh/test/v7l/neon/vfp:/home/cnb1szh/test/v7l/neon:/home/cnb1szh/test/v7l/vfp:/home/cnb1szh/test/v7l:/home/cnb1szh/test/neon/vfp:/home/cnb1szh/test/neon:/home/cnb1szh/test/vfp:/home/cnb1szh/test
(RPATH from file ./hello)

30693: trying file=/home/cnb1szh/test/tls/v7l/neon/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/v7l/neon/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/v7l/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/v7l/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/neon/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/neon/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/tls/libmytest.so

30693: trying file=/home/cnb1szh/test/v7l/neon/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/v7l/neon/libmytest.so

30693: trying file=/home/cnb1szh/test/v7l/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/v7l/libmytest.so

30693: trying file=/home/cnb1szh/test/neon/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/neon/libmytest.so

30693: trying file=/home/cnb1szh/test/vfp/libmytest.so

30693: trying file=/home/cnb1szh/test/libmytest.so

but we don't have /home/cnb1szh/test/tls/, /home/cnb1szh/test/v7l/,
/home/cnb1szh/test/vfp/, /home/cnb1szh/test/neon/, why does the ld.so
search so many paths?

-barry
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Hi Barry, this is a known, intentional behavior of the dynamic-linker.

It defaults to searching for libraries in a tls directory (the glibc developers intend to remove this since linux-threads are now gone and nptl is the standard but no-one has stepped forward to do so), then directories based on the cpu, then directories that are based on the hardware capabilities for the platform (AT_HWCAP for 'arm') in various combinations. This is why you see it searching the different variations of directories.

This is not a bug.

What this does is allows the Linux distribution to provide optimized versions of the libraries in each of those directories. The optimized versions of the library have the most efficient code-gen for the capability present. For instance, in your own library, if you wanted to have a neon optimized version and a non-neon optimized version you'd put the neon one in test/neon/ and the non-optimized version in test/ directly.

Ryan S. Arnold
Linaro Toolchain Working Group - Engineering Manager
www.linaro.org