[PATCH] D77330: Consider increasing the default ARM32 page size to 64k.

[Tobias Hieta via Phabricator via llvm-commits]

thieta added a comment.

Hello Nick,

Maybe I am using the wrong terminology here and in that case I am sorry. What I mean is the default max page size for the arm32 target in lld. Here is the tests I can boil it down to:

Consider hello.c

  #include <stdio.h>
  
  int main(int argc, char** argv)
  {
    printf("Hello World!\n");
    return 0;
  }

I build this three different ways:

With lld no arguments about max page size:

  clang --target=arm-linux-gnueabi -march=armv7-a -mthumb -mfloat-abi=soft -mfpu=vfpv3-d16 --sysroot=$TOOLCHAIN_DIR/arm-linux-gnueabi/libc --gcc-toolchain=$TOOLCHAIN_DIR hello.c -o hello-lld -fuse-ld=lld

With ld.bfd:

  clang --target=arm-linux-gnueabi -march=armv7-a -mthumb -mfloat-abi=soft -mfpu=vfpv3-d16 --sysroot=$TOOLCHAIN_DIR/arm-linux-gnueabi/libc --gcc-toolchain=$TOOLCHAIN_DIR hello.c -o hello-bfd -fuse-ld=bfd

And finally with lld and max-page-size argument:

  clang --target=arm-linux-gnueabi -march=armv7-a -mthumb -mfloat-abi=soft -mfpu=vfpv3-d16 --sysroot=$TOOLCHAIN_DIR/arm-linux-gnueabi/libc --gcc-toolchain=$TOOLCHAIN_DIR hello.c -o hello -fuse-ld=lld -Wl,-max-page-size=0x10000

I copied them over to the device and ran them:

  root at WD-EX2100 root # ./hello-bfd
  Hello World!
  root at WD-EX2100 root # ./hello-lld
  Killed
  root at WD-EX2100 root # ./hello-lld-max-page
  Hello World!
  root at WD-EX2100 root #

As you see it works when we set the max-page-size, we can also verify this quickly with readelf:

  ➜ readelf -a hello-bfd | grep LOAD
    LOAD           0x000000 0x00010000 0x00010000 0x0043c 0x0043c R E 0x10000
    LOAD           0x00043c 0x0002043c 0x0002043c 0x0011c 0x00120 RW  0x10000
  
  ➜ readelf -a hello-lld | grep LOAD
    LOAD           0x000000 0x00010000 0x00010000 0x003e4 0x003e4 R   0x1000
    LOAD           0x0003e4 0x000113e4 0x000113e4 0x001cc 0x001cc R E 0x1000
    LOAD           0x0005b0 0x000125b0 0x000125b0 0x000d8 0x000d8 RW  0x1000
    LOAD           0x000688 0x00013688 0x00013688 0x00024 0x00025 RW  0x1000
  
  ➜ readelf -a hello-lld-max-page | grep LOAD
    LOAD           0x000000 0x00010000 0x00010000 0x003e4 0x003e4 R   0x10000
    LOAD           0x0003e4 0x000203e4 0x000203e4 0x001cc 0x001cc R E 0x10000
    LOAD           0x0005b0 0x000305b0 0x000305b0 0x000d8 0x000d8 RW  0x10000
    LOAD           0x000688 0x00040688 0x00040688 0x00024 0x00025 RW  0x10000

And just to confirm the device have the following page size configuration:

  root at WD-EX2100 root # getconf PAGESIZE
  32768

And we can try it on another device with another page size configuration:

  root at Netgear-RN102:~# getconf PAGESIZE
  4096
  root at Netgear-RN102:~# ./hello-lld
  Hello World!
  root at Netgear-RN102:~# ./hello-bfd
  Hello World!
  root at Netgear-RN102:~# ./hello-lld-max-page
  Hello World!

Hope this was the information you where looking for.

I also uploaded the binaries here: https://artifacts.plex.tv/testing/page_size_tests.tar.gz


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D77330/new/

https://reviews.llvm.org/D77330