gcc plugins with arm64 cross compiler : cannot open shared object file

I am trying to compute the sizes of each struct at compile time using a gcc plugin. Searching, I came across this article.

I tried it out on a test program below with my native x64 gcc compiler and got the following results.

#include <stdio.h>

struct TEST {
  int a;
  unsigned long b;
  char p[100];
};

int main(int argc, const char *argv[])
{
  struct TEST t;

  t.a = 10;

  t.a += 1;

  scanf("%s", t.p);
  scanf("%lu", &t.b);
  scanf("%d", &t.a);

  printf("%d\n", t.a);

  return 0;
}

Results :-

Loaded structsizes plugin (GCC 5.4.0..)
ignoring unnamed struct
struct '_IO_FILE' has incomplete type
struct '_IO_FILE' has incomplete type
struct '_IO_FILE' has incomplete type
ignoring unnamed struct
ignoring unnamed struct
ignoring unnamed struct
struct '_IO_jump_t' has incomplete type
struct '_IO_FILE' has incomplete type
struct '_IO_marker' has incomplete type
struct '_IO_FILE' has incomplete type
struct '_IO_marker' has size 192 [bits]
struct '_IO_marker' has size 192 [bits]
struct '_IO_FILE' has incomplete type
struct '_IO_FILE' has size 1728 [bits]
struct '_IO_FILE' has size 1728 [bits]
struct '_IO_FILE_plus' has incomplete type
struct '_IO_FILE_plus' has incomplete type
struct '_IO_FILE_plus' has incomplete type
struct '_IO_FILE_plus' has incomplete type
struct '_IO_FILE' has size 1728 [bits]
struct '_IO_FILE' has size 1728 [bits]
struct '_IO_FILE' has size 1728 [bits]
struct 'TEST' has size 960 [bits]
struct 'TEST' has size 960 [bits]

Now I try the same for my aarch64 cross compiler. The version of the cross compiler I have is :-

> aarch64-linux-gnu-gcc --version                                                                                                                       
aarch64-linux-gnu-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.1) 5.4.0 20160609

I compile the gcc plugin as :-

$ aarch64-linux-gnu-gcc -g -I/usr/lib/gcc-cross/aarch64-linux-gnu/5/plugin/include -fpic -shared -o structsizes.so structsizes.cc

$ file structsizes.so
structsizes.so: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, BuildID[sha1]=64b00b52af267537f94d8c4c651f3235e7c7b722, not stripped

Now, I try to compile test.c as :-

$ aarch64-linux-gnu-gcc -fplugin=./structsizes.so -fplugin-arg-structsizes-log=/tmp/logfile -o test test.c
cc1: error: cannot load plugin ./structsizes.so
./structsizes.so: cannot open shared object file: No such file or directory

Why does this error occur? I tried it with a linaro binary toolchain that I downloaded as well and got the same error. What am I missing?

The plugin runs as part of the compiler, so still needs to be built for the host machine, regardless of what the target of that compiler might be. Whilst it's more than happy to build them, as an x86 program itself your cross-compiler can't actually use an AArch64 shared object, as it tells you.