Calling Global Constructors: Difference between revisions
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To understand this apparent complexity, consider a program consisting of <tt>foo.o</tt> and <tt>bar.o</tt> that is being linked: |
To understand this apparent complexity, consider a program consisting of <tt>foo.o</tt> and <tt>bar.o</tt> that is being linked: |
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<source lang="bash"> |
<source lang="bash">i586-elf-gcc foo.o bar.o -o program</source> |
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The compiler will rewrite the command line and pass it to the linker as: |
The compiler will rewrite the command line and pass it to the linker as: |
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<source lang="bash"> |
<source lang="bash">i586-elf-ld crt0.o crti.o crtbegin.o foo.o bar.o crtend.o crtn.o</source> |
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The idea is that the these files together form the <tt>_init</tt> and <tt>_fini</tt> functions during the linking. This is done by storing the <tt>_init</tt> function in the <tt>.init</tt> section, and the <tt>_fini</tt> function in the <tt>.fini section</tt>. Each file then contributes a bit to these sections and the linker makes glues together the fragments in the code specified on the command line. <tt>crti.o</tt> provides the function header, <tt>crtbegin.o</tt> and <tt>crtend.o</tt> provide the body, and <tt>crtn.o</tt> provide the footer (return statement). It is important to understand that the link order matters and strange things may happen if the objects is not exactly linked in this order. |
The idea is that the these files together form the <tt>_init</tt> and <tt>_fini</tt> functions during the linking. This is done by storing the <tt>_init</tt> function in the <tt>.init</tt> section, and the <tt>_fini</tt> function in the <tt>.fini section</tt>. Each file then contributes a bit to these sections and the linker makes glues together the fragments in the code specified on the command line. <tt>crti.o</tt> provides the function header, <tt>crtbegin.o</tt> and <tt>crtend.o</tt> provide the body, and <tt>crtn.o</tt> provide the footer (return statement). It is important to understand that the link order matters and strange things may happen if the objects is not exactly linked in this order. |
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