How to do a reverse offset/index in x86 [duplicate]

问题

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Closed 4 months ago.

I am trying to do a negative offset for memory addressing. This is to convert a number to a string and make sure that it doesn't print in reverse order since x86 is little endian. Here is what I'm trying to do:

 # (b) move the asci number to rbp-8-len (to print in reverse)
 movb %al,  -8(%rbp, %r12, -1)

I know -1 is not a valid size, but I've shown what I'm trying to do conceptually above. What would be the proper way to do this?

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Currently, I am doing it like:

# (b) move the asci number to rbp-8-len (to print in reverse)
# store offset (8+len) in %r13
mov $-8,        %r13
sub %r12,       %r13
movb %dl,       (%rbp, %r13)

来源：https://stackoverflow.com/questions/63965249/how-to-do-a-reverse-offset-index-in-x86