Question

I am wonder why these two commands return two different results. First one is:

[root@node30 par-run-d2]# make -C NQU/
make: Entering directory `/home/ut/gpgpu-sim/benchmarks/par-run-d2/NQU'
nvcc  -c -arch sm_11 --keep --compiler-options -fno-strict-aliasing \
        -I. -I/usr/local/cuda//include/ -I/home/ut/NVIDIA_GPU_Computing_SDK/C//common/inc/ \
          -L/home/ut/NVIDIA_GPU_Computing_SDK/C//lib -lcutil -DUNIX nqueen.cu -o nqueen 
nqueen.cu(681): warning: variable "start" was declared but never referenced

nqueen.cu(681): warning: variable "end" was declared but never referenced

nqueen.cu(681): warning: variable "start" was declared but never referenced

nqueen.cu(681): warning: variable "end" was declared but never referenced

gcc -g -c nqueen.cu.cpp -o nqueen.cu_o
echo ../../..
../../..
../../../scripts/gen_ptxinfo
Generating nqueen.ptxinfo...
make: *** [nqueen.cu_o] Error 255
make: Leaving directory `/home/ut/gpgpu-sim/benchmarks/par-run-d2/NQU'

And the second one is:

[root@node30 par-run-d2]# cd NQU/
[root@node30 NQU]# make
g++  -g nqueen.cu_o -L../../../libcuda/ -lcuda \
        -L/home/ut/NVIDIA_GPU_Computing_SDK/C//lib -lcutil \
        -L../../../src/ -lgpgpusim \
        -L../../../src/intersim -lintersim \
        -L../../../src/cuda-sim/ -lgpgpu_ptx_sim \
        -lm -lz -lGL   -o gpgpu_ptx_sim__nqueen
rm -rf *.cpp*.i *.cpp*.ii *.cu.c *.cudafe*.* *.fatbin.c *.cu.cpp *.linkinfo *.cpp_o core *.cubin cubin.bin *_o *.hash nqueen

Any idea why “make -C X” differs from “cd X/; make” ?

Answer 1

The sequence cd X; make is changing the current directory of the invoking shell (the interactive shell of your terminal). Make that a sub-shell like (cd X; make) to avoid that, which is much longer to type than make -C X which does the chdir syscall inside the make process so cannot change the working directory of the parent process (your interactive shell usually).

Also the -w flag behavior would be different. And most recursive $(MAKE) in Makefile-s are doing a -C somesubdir

PS. Remember that the cd shell built-in invokes the chdir(2) syscall which has no effect on the parent process.