Analysis of Embedded Assembly Applets in arm-linux

Analysis of arm-linux Embedded Assembly applet-general Linux technology-Linux programming and kernel information. The following is a detailed description. # Define _ range_ OK (addr, size )({\
Unsigned long flag, sum ;\
_ Asm _ ("adds % 1, % 2, % 3; sbcccs % 1, % 1, % 0; movcc % 0, #0 "\
: "= & R" (flag), "= & r" (sum )\
: "R" (addr), "Ir" (size), "0" (current-> addr_limit )\
: "Cc ");\
Flag ;})
Understanding of Embedded Assembly:
// Remember gliethttp 7.7
1. "= & r" (flag)
1.1 & indicates that the output data will not be overwritten
1.2 = & r (flag) % 0 flag is the output unit. r indicates that the Register r is used as the reference of the flag variable, rather than memory, which is volatile.
2. "= &" (sum) % 1 sum is the output unit, and the r register is used as the reference of sum.
3. "r" (addr) % 2 the input unit variable addr is referenced in the r register
4. "Ir" (size) % 3 the size of the 32-bit input unit is referenced in the r register.
5. "0" (current-> addr_limit) % 4 enter the unit variable current-> addr_limit to reference with the r register of % 0,
That is, before entering the _ asm _ Embedded Assembly command, the input variable % 4 is assigned a value, that is, the r register of % 0 is assigned a value of current-> addr_limit.
6. "cc" the embedded _ asm _ Assembly command will change the CPU condition Status Register cc
7. flag; tell the gcc compiler that the flag serves as the final return value of the output variable unit, that is, sum is only the intermediate amount of the output unit,
If there is only one output unit, the flag is unnecessary;
However, there is also a flag = 0; this means that the comparison result of flag = 0; is used as the final output return value.