[GitHub] [incubator-nuttx] patacongo commented on issue #3751: nucleo-h743zi:elf config got broken (nsh: nsh_session: readline failed: 13)

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patacongo commented on issue #3751:
URL: https://github.com/apache/incubator-nuttx/issues/3751#issuecomment-845343585


   > [468e08c](https://github.com/apache/incubator-nuttx/commit/468e08c1b4ff1441cf898623782869c7daf1c947) is the first bad commit
   > [e5f1069](https://github.com/apache/incubator-nuttx/commit/e5f10696541dcbd53337b90f53538a48d073b4bc) is the last good commit
   
   When I first looked, 468e08c seemed like an unlikely cause of the problem.  That commit simply changes some error handling if the ELF load fails.  The ELF loader simply calls `elf_uninit()` in the event of a failure:
   
       65 int elf_uninit(struct elf_loadinfo_s *loadinfo)
       66 {
       67   /* Free all working buffers */
       68
       69   elf_freebuffers(loadinfo);
       70
       71   /* Close the ELF file */
       72
       73   if (loadinfo->filfd >= 0)
       74     {
       75       nx_close(loadinfo->filfd);
       76     }
       77
       78   return OK;
       79 }
   
   You see a failure that is attributed to readline() which seems unrelated:
   
       79 #define EACCES              13
       80 #define EACCES_STR          "Permission denied"
   
   The error is reported, apparently, by logic in `apps/nshlib/nsh_stdsession.c` if a call to `readline()` returns EOF.  `readline()` ultimately calls `read()` on stdin (file descriptor 0).  `EACCES` is returned from `read()` if the file is not opened for reading:
   
       71   /* Was this file opened for read access? */
       72
       73   if ((filep->f_oflags & O_RDOK) == 0)
       74     {
       75       /* No.. File is not read-able */
       76
       77       ret = -EACCES;
       78     }
       79
   
   So now I think I see how this commit can cause this error to be seen:
   
   1. When ELF support is enabled, NSH will always first attempt to a program with that command name at the PATH directory.  For example, `nsh> ls` will attempt to run at `/bin/ls`
   2. In this case it will fail to run the problem and will fail silently.  It will call `elf_unit()` which will close the file at descriptor `loadinfo->filfd`.  But that file descriptor has not been initialized and is still at its initial state; of zero:
   
       elf_init():
       136   memset(loadinfo, 0, sizeof(struct elf_loadinfo_s));
   
   3. So `stdin` will be closed (via close -> nx_close -> file_close).
   4. After this fails, then readline() is called which will attempt to `read()` from `stdin`. But `read()` will fail will errno `EACCES` because stdin is no open for writing.
   
   
   


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