|Red Hat Enterprise Linux 4: Developer Tools Guide|
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The compiler normally turns a text based source file into a binary object file. It is possible however to instruct it to just convert the source code into assembler and stop there. The -S option does this. It also possible to instruct the compiler to produce an assembler listing as well as an object file. That can be done as follows:
gcc -c -O2 -Wa,-al hello.c
-c tells GCC to compile or assemble source files, but not to link them. -O2 produces more fully optimized code. These are both optional. -Wa tells the compiler to pass the comma-separated list of options which follows it on to the assembler. The -al option is an assembler option to request an assembler listing.
This example shows a partial excerpt of an assembler listing for an x386-based target.
29 .text 30 0027 90 .p2align 2,,3 31 .globl main 32 .type main,@function 33 main: 34 0028 55 pushl %ebp 35 0029 89E5 movl %esp, %ebp 36 002b 83EC08 subl $8, %esp 37 002e 83E4F0 andl $-16, %esp 38 0031 83EC0C subl $12, %esp 39 0034 680E0000 pushl $.LC1 39 00 40 0039 C7050000 movl $3, a 40 00000300 40 0000 41 0043 E8FCFFFF call puts 41 FF 42 0048 C7042404 movl $4, (%esp)
Example 3-2. Assembly listing excerpt
It also possible to produce an assembler listing that intermixes the original input source code with the assembler instructions produced by the compiler. This can help track down bugs, discover how the compiler handles certain language constructs (such as function calls) and to learn more about assembly language. To do this, just add an h to the assembler option like this:
gcc -c -g -O2 -Wa,-alh hello.c