as --help
-a[sub-option...] turn on listings
Sub-options [default hls]:
c omit false conditionals
d omit debugging directives
g include general info
h include high-level source
l include assembly
m include macro expansions
n omit forms processing
s include symbols
=FILE list to FILE (must be last sub-option)

gcc -c -O2 hoge.c -Wa,-ahls=hoge.lst