1 前置背景

最近在基于目前已有的rt-thread构建框架，改造设计一套新的软件架构及构建，基于RA系列的BSP，使用scons的构建方式在windows的env环境下推进。

在这期间，参考了社区帖子 scons如何指定输出目录 , 基本能够实现将编译输出的obj文件导到编译输出目录，而不是在原来的源码目录。

但是，我发现了一个个例，以 bsp\renesas\ra2l1-cpk 为例，在它的原生的rt-thread env构建流程中也是存在这样的问题。

见下面执行scons的编译出：

CC build\kernel\src\kservice.o
CC build\kernel\src\mem.o
CC build\kernel\src\mempool.o
CC build\kernel\src\object.o
CC build\kernel\src\scheduler.o
CC build\kernel\src\thread.o
CC build\kernel\src\timer.o
CC build\ra_gen\common_data.o
CC build\ra_gen\hal_data.o
CC build\ra_gen\main.o
CC build\ra_gen\pin_data.o
CC build\ra_gen\vector_data.o
CC build\src\hal_entry.o
CC ra\fsp\src\bsp\cmsis\Device\RENESAS\Source\startup.o
CC ra\fsp\src\bsp\cmsis\Device\RENESAS\Source\system.o
CC ra\fsp\src\bsp\mcu\all\bsp_clocks.o
CC ra\fsp\src\bsp\mcu\all\bsp_common.o
CC ra\fsp\src\bsp\mcu\all\bsp_delay.o
CC ra\fsp\src\bsp\mcu\all\bsp_group_irq.o
CC ra\fsp\src\bsp\mcu\all\bsp_guard.o
CC ra\fsp\src\bsp\mcu\all\bsp_io.o
CC ra\fsp\src\bsp\mcu\all\bsp_irq.o
CC ra\fsp\src\bsp\mcu\all\bsp_register_protection.o
CC ra\fsp\src\bsp\mcu\all\bsp_rom_registers.o
CC ra\fsp\src\bsp\mcu\all\bsp_sbrk.o
CC ra\fsp\src\bsp\mcu\all\bsp_security.o
CC ra\fsp\src\r_icu\r_icu.o
CC ra\fsp\src\r_ioport\r_ioport.o
CC ra\fsp\src\r_sci_uart\r_sci_uart.o
CC D:\llc\git_repos\rt-thread-share\rt-thread-share\rtt-5.0\rt-thread\bsp\renesas\libraries\HAL_Drivers\drv_common.o
CC D:\llc\git_repos\rt-thread-share\rt-thread-share\rtt-5.0\rt-thread\bsp\renesas\libraries\HAL_Drivers\drv_gpio.o
CC D:\llc\git_repos\rt-thread-share\rt-thread-share\rtt-5.0\rt-thread\bsp\renesas\libraries\HAL_Drivers\drv_usart_v2.o
D:\llc\git_repos\rt-thread-share\rt-thread-share\rtt-5.0\rt-thread\bsp\renesas\libraries\HAL_Drivers\drv_usart_v2.c: In function 'ra_uart_transmit':
D:\llc\git_repos\rt-thread-share\rt-thread-share\rtt-5.0\rt-thread\bsp\renesas\libraries\HAL_Drivers\drv_usart_v2.c:260:21: warning: variable 'uart' set but not used [-Wunused-but-set-variable]
  260 |     struct ra_uart *uart;
      |                     ^~~~
LINK rtthread.elf
arm-none-eabi-objcopy -O ihex rtthread.elf rtthread.hex
arm-none-eabi-size rtthread.elf
   text    data     bss     dec     hex filename
  87364    1592    4728   93684   16df4 rtthread.elf
scons: done building targets.

注意看 ra目录下的几个obj文件，比如（CC ra\fsp\src\bsp\mcu\all\bsp_clocks.o），输出都是在源码目录，而其他的与ra同级的目录，比如ra_gen都是在build目录往下存放（rt-thread的build tool默认将obj文件放在build目录）。

起初，我以为是ra目录下的SConscript文件和ra_gen目录下的SConscript文件有些区别，但我看了内容了，实在没想明白，为啥ra目录下的源码编译输出的obj文件就在源码目录，而ra_gen目录的源码却不会这样。

bsp顶级目录的SConscript文件内容：

# for module compiling
import os
Import('RTT_ROOT')
Import('rtconfig')
from building import *
cwd = GetCurrentDir()
src = []
CPPPATH = []
list = os.listdir(cwd)
if rtconfig.PLATFORM in ['iccarm']:
    print("\nThe current project does not support IAR build\n")
    Return('group')
elif rtconfig.PLATFORM in ['gcc', 'armclang']:
    if GetOption('target') != 'mdk5':
        CPPPATH = [cwd + './src']
        src = Glob('./src/*.c')
group = DefineGroup('Applications', src, depend = [''], CPPPATH = CPPPATH)
for d in list:
    path = os.path.join(cwd, d)
    if os.path.isfile(os.path.join(path, 'SConscript')):
        group = group + SConscript(os.path.join(d, 'SConscript'))
Return('group')

ra目录下的SConscript文件内容：

Import('RTT_ROOT')
Import('rtconfig')
from building import *
cwd = GetCurrentDir()
src = []
group = []
CPPPATH = []
if rtconfig.PLATFORM in ['iccarm']:
    print("\nThe current project does not support IAR build\n")
    Return('group')
elif rtconfig.PLATFORM in ['gcc', 'armclang']:
    if GetOption('target') != 'mdk5':
        src += Glob(cwd + '/fsp/src/bsp/mcu/all/*.c')
        src += [cwd + '/fsp/src/bsp/cmsis/Device/RENESAS/Source/system.c']
        src += [cwd + '/fsp/src/bsp/cmsis/Device/RENESAS/Source/startup.c']
        src += Glob(cwd + '/fsp/src/r_*/*.c')
        CPPPATH = [ cwd + '/arm/CMSIS_5/CMSIS/Core/Include',
                    cwd + '/fsp/inc',
                    cwd + '/fsp/inc/api',
                    cwd + '/fsp/inc/instances',]
group = DefineGroup('ra', src, depend = [''], CPPPATH = CPPPATH)
Return('group')
ra_gen目录下的SConscript文件内容：

Import('RTT_ROOT')
Import('rtconfig')
from building import *
cwd = GetCurrentDir()
src = []
group = []
CPPPATH = []
if rtconfig.PLATFORM in ['iccarm']:
    print("\nThe current project does not support IAR build\n")
    Return('group')
elif rtconfig.PLATFORM in ['gcc', 'armclang']:
    if GetOption('target') != 'mdk5':
        src = Glob('*.c')
        CPPPATH = [cwd, ]
group = DefineGroup('ra_gen', src, depend = [''], CPPPATH = CPPPATH)
Return('group')