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Diffstat (limited to 'nuttx/libc/README.txt')
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1 files changed, 85 insertions, 0 deletions
diff --git a/nuttx/libc/README.txt b/nuttx/libc/README.txt new file mode 100644 index 000000000..ed672d038 --- /dev/null +++ b/nuttx/libc/README.txt @@ -0,0 +1,85 @@ +lib +=== + +This directory contains numerous, small functions typically associated with +what you would expect to find in a standard C library. The sub-directories +in this directory contain standard interface that can be executed by user- +mode programs. + +Normally, NuttX is built with no protection and all threads running in kerne- +mode. In that model, there is no real architectural distinction between +what is a kernel-mode program and what is a user-mode program; the system is +more like on multi-threaded program that all runs in kernel-mode. + +But if the CONFIG_NUTTX_KERNEL option is selected, NuttX will be built into +distinct user-mode and kernel-mode sections. In that case, most of the +code in the nuttx/ directory will run in kernel-mode with with exceptions +of (1) the user-mode "proxies" found in syscall/proxies, and (2) the +standard C library functions found in this directory. In this build model, +it is critical to separate the user-mode OS interfaces in this way. + +Sub-Directories +=============== + +The files in the libc/ directory are organized (mostly) according which file +in the include/ directory provides the prototype for library functions. So +we have: + + libgen - libgen.h + fixedmath - fixedmath.h + math - math.h + mqueue - pthread.h + net - Various network-related header files: netinet/ether.h, arpa/inet.h + pthread - pthread.h + queue - queue.h + sched - sched.h + semaphore - semaphore.h + stdio - stdio.h + stdlib - stdlib.h + string - string.h + time - time.h + unistd - unistd.h + +There is also a misc/ subdirectory that contains various internal functions +and interfaces from header files that are too few to warrant their own sub- +directory: + + misc - Nonstandard "glue" logic, debug.h, crc32.h, dirent.h + +Library Database +================ + +Information about functions available in the NuttX C library information is +maintained in a database. That "database" is implemented as a simple comma- +separated-value file, lib.csv. Most spreadsheets programs will accept this +format and can be used to maintain the library database. + +This library database will (eventually) be used to generate symbol library +symbol table information that can be exported to external applications. + +The format of the CSV file for each line is: + + Field 1: Function name + Field 2: The header file that contains the function prototype + Field 3: Condition for compilation + Field 4: The type of function return value. + Field 5 - N+5: The type of each of the N formal parameters of the function + +Each type field has a format as follows: + + type name: + For all simpler types + formal type | actual type: + For array types where the form of the formal (eg. int parm[2]) + differs from the type of actual passed parameter (eg. int*). This + is necessary because you cannot do simple casts to array types. + formal type | union member actual type | union member fieldname: + A similar situation exists for unions. For example, the formal + parameter type union sigval -- You cannot cast a uintptr_t to + a union sigval, but you can cast to the type of one of the union + member types when passing the actual paramter. Similarly, we + cannot cast a union sigval to a uinptr_t either. Rather, we need + to cast a specific union member fieldname to uintptr_t. + +NOTE: The tool mksymtab can be used to generate a symbol table from this CSV +file. See nuttx/tools/README.txt for further details about the use of mksymtab. |