Make the client shim a no-op on reMarkable 1

[matteodelabre]

This PR is intended to make it safe to load the librm2fb_client library even when running on reMarkable 1. This is so that Toltec can ship all the binaries that need to access the framebuffer with a dynamic dependency on librm2fb_client, and eliminate the need to set the LD_PRELOAD environment variable when starting those binaries.

In the library constructor, the /sys/devices/soc0/machine file is read to determine whether we’re running on rM1 or rM2, and set the ON_RM2 flag accordingly. When this flag is off, the wrapped system calls directly forward their arguments to the standard library.

I also cleaned up some parts of the existing code, in particular:

• Removed repeated function pointer types, when possible.
• Moved most file globals to block-level static variables.
• Removed the main function definition that looked redundant.

Test plan:

• Built librm2fb_client.so.1.0.0 and checked that the exported symbols did not change compared to the last version (using arm-oe-linux-gnueabi-objdump -T librm2fb_client.so.1.0.0 | grep "DF .text"), except for the removed main symbol:
  • _ZN6QImageC1EiiNS_6FormatE
  • _Z7qputenvPKcRK10QByteArray
  • ioctl
  • open64
  • open
  • close
  • __libc_start_main
• On rM1, ran LD_PRELOAD=./librm2fb_client.so.1.0.0 xochitl, checked that no preloading errors occurred and that no messages from the shim appeared. Checked that the display worked correctly and that the touchscreen was not inverted.
• On rM1, ran LD_PRELOAD=./librm2fb_client.so.1.0.0 calculator and performed the same checks as in the previous item.
• On rM2, ran LD_PRELOAD=./librm2fb_client.so.1.0.0 xochitl and checked that no preloading errors occurred, and that the following messages from the shim appeared:

OPENED SHARED MEM: /dev/shm/swtfb.01 at 72c2e000, errno: 0
Update fn address: 0x2c050c
Create th address: 0x2c2798
Wait for th address: 0x2c1fd4
shutdown address: 0x2c273c
REPLACING THE IMAGE with shared memory
create threads called
wait clear func called

Also checked that the display worked correctly and that the touchscreen was not inverted.

• On rM2, ran LD_PRELOAD=./librm2fb_client.so.1.0.0 calculator and checked that no preloading errors occurred, that the display worked correctly, and that the touchscreen was not inverted.

[matteodelabre]

Thanks for the review!

Moved most file globals to block-level static variables.

what is this referring to?

There were some globals like qImageCtor, FIRST_ALLOC, touchArgs, … that were defined with file visibility although they were only used in one specific function. I moved each of those definitions inside the relevant function.

[raisjn]

let's give this thorough testing in the toltec upgrade