[PR] arch/arm: fix the error in retrieving thread pointerafter we use `-mtp=soft` [nuttx]

["suoyuanG (via GitHub)" <gi...@apache.org>]

suoyuanG opened a new pull request, #17815:
URL: https://github.com/apache/nuttx/pull/17815

   ## Summary
   
   Fix #17040
   
   In https://github.com/ARM-software/abi-aa/blob/main/rtabi32/rtabi32.rst#thread-local-storage-new-in-v2-01, we know that `__aeabi_read_tp` cannot modify registers $r1\~$r3, so we need to use assembly implementation instead of C functions.
   
   As #17040 mentioned here, our current implementation modifies the $r1\~r3 register, but the compiler generates code based on the assumption that the function will not modify $r1~$r3. Therefore, you might find that your thread_local is causing problems, which is very likely due to this. I will provide an example below to reproduce the problem.
   
   Secondly, we changed `_stdata`  and `_stbss` to `uint_8`, but the TLS initialization here doesn't synchronize this change; it still follows the assumption that they are `uint32_t`. We need to modify this and adapt for any padding that might exist between the two sections to accurately perform TLS initialization.
   
   ## Testing
   
   In qemu-armv7a:nsh:
   
   First, you need to apply the following patch to  link script:
   
   ```patch
   diff --git a/boards/arm/qemu/qemu-armv7a/scripts/dramboot.ld b/boards/arm/qemu/qemu-armv7a/scripts/dramboot.ld
   index 19e481ecd6..de0104fad9 100644
   --- a/boards/arm/qemu/qemu-armv7a/scripts/dramboot.ld
   +++ b/boards/arm/qemu/qemu-armv7a/scripts/dramboot.ld
   @@ -93,6 +93,18 @@ SECTIONS
          _erodata = .;
      } > ROM
    
   +  .tdata : {
   +      _stdata = ABSOLUTE(.);
   +      *(.tdata .tdata.* .gnu.linkonce.td.*);
   +      _etdata = ABSOLUTE(.);
   +  } > ROM
   +
   +  .tbss : {
   +      _stbss = ABSOLUTE(.);
   +      *(.tbss .tbss.* .gnu.linkonce.tb.* .tcommon);
   +      _etbss = ABSOLUTE(.);
   +  } > ROM
   +
      _eronly = LOADADDR(.data);
      .data : {                    /* Data */
          _sdata = .;
   ```
   
   Then, we can use the following code:
   
   ```c
   #include <nuttx/config.h>
   #include <stdio.h>
   #include <pthread.h>
   #include <unistd.h>
   #include <threads.h>
   
   thread_local int hello_counter = 0;
   
   static void *thread_function(void *arg)
   {
     int thread_id = *(int *)arg;
   
     for (int i = 0; i < 5; i++)
       {
         hello_counter++;
         printf("Thread %d: hello_counter = %d, where is located at: %p\n", thread_id, hello_counter, (void *)&hello_counter);
         usleep(100000);
       }
   
     printf("Thread %d final counter: %d\n", thread_id, hello_counter);
     return NULL;
   }
   
   int main(int argc, FAR char *argv[])
   {
     pthread_t thread1, thread2, thread3;
     int id1 = 1, id2 = 2, id3 = 3;
   
     pthread_create(&thread1, NULL, thread_function, &id1);
     pthread_create(&thread2, NULL, thread_function, &id2);
     pthread_create(&thread3, NULL, thread_function, &id3);
   
     pthread_join(thread1, NULL);
     pthread_join(thread2, NULL);
     pthread_join(thread3, NULL);
   
     // printf("hello_counter in main thread is located at: %p\n", (void *)&hello_counter);
     printf("Main thread: hello_counter = %d (unmodified)\n", hello_counter);
     printf("Thread-local demo completed!\n");
   
     return 0;
   }
   ```
   
   Finally, you need to enable `CONFIG_SCHED_THREAD_LOCAL`, and  your GCC must be compiled using `--enable-tls` .
   
   ```bash
   $ arm-none-eabi-objdump --disassemble=hello_main build/nuttx
   ...
      226b4:	eb0028ec 	bl	2ca6c <pthread_join>
      226b8:	e59f3024 	ldr	r3, [pc, #36]	@ 226e4 <hello_main+0xa4>
      226bc:	ebffa8fa 	bl	caac <__aeabi_read_tp>
      226c0:	e7931000 	ldr	r1, [r3, r0]
      226c4:	e59f001c 	ldr	r0, [pc, #28]	@ 226e8 <hello_main+0xa8>
   ...
   ```
   
   Running this nuttx will result in loading an inaccessible address, because $r3 was originally an offset for the Thread Pointer, but  $r3 will be modified to a different value after calling `__aeabi_read_tp`.
   
   I have run ostest in qemu-armv7a:nsh and there are no errors.
   
   > You might find you can't reproduce this issue, and `__aeabi_read_tp` isn't even in nuttx. This is because the compiler might not generate code for Arm-A by default that uses `__aeabi_read_tp` to obtain the thread pointer. You need to add the `-mtp=soft` compiler parameter to use `__aeabi_read_tp` as the method for obtaining the thread pointer. In fact, I want to submit another patch to fix this.
   >
   > https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-mtp
   
   


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Re: [PR] arch/arm: fix the error in obtaining thread pointer after we use `-mtp=soft` [nuttx]

["xiaoxiang781216 (via GitHub)" <gi...@apache.org>]

xiaoxiang781216 merged PR #17815:
URL: https://github.com/apache/nuttx/pull/17815


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