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    <p>First of all, as other said you should consider using a DLL or SO.</p> <p>That said, if you really want to do this, you need to replace the linker script. Something like this (not very well tested, but I think it works):</p> <pre><code>ENTRY(_dummy_start) SECTIONS { _dummy_start = 0; _GLOBAL_OFFSET_TABLE_ = 0; .all : { _all = .; LONG(f1 - _all); *( .text .text.* .data .data.* .rodata .rodata.* ) } } </code></pre> <p>Then compile with:</p> <pre><code>$ gcc -c -fPIC test.c </code></pre> <p>Link with:</p> <pre><code>$ ld -T script.ld test.o -o test.elf </code></pre> <p>And extract the binary blob with:</p> <pre><code>$ objcopy -j .all -O binary test.elf test.bin </code></pre> <p>Probably some explanation of the script is welcome:</p> <ul> <li><code>ENTRY(_dummy_start)</code> That just avoids the warning about the program not having an entry point.</li> <li><code>_dummy_start = 0;</code> That defines the symbol used in the previous line. The value is not used.</li> <li><code>_GLOBAL_OFFSET_TABLE_ = 0;</code> That prevents another linker error. I don't think you really need this symbol, so it can be defined as 0.</li> <li><code>.all</code> That's the name of the section that will collect all the bytes of your blob. In this sample it will be all the <code>.text</code>, <code>.data</code> and <code>.rodata</code> sections together. You may need some more if you have complicated functions, in this case <code>objdump -x test.o</code> is your friend.</li> <li><code>LONG(f1 - _all)</code> Not really needed, but you want to know the offset of your function into the blob, don't you? You cannot assume that it will be at offset 0. With this line the very first 4 bytes in the blob will be the offset of the symbol <code>f1</code> (your function). Change <code>LONG</code> with <code>QUAD</code> if using 64-bit pointers.</li> </ul> <p><strong>UPDATE</strong>: And now a quick'n'dirty test (it works!):</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;sys/mman.h&gt; typedef void (*f1_t)(char *a, char *b, int len); f1_t f1; int main() { char *blob = (char*)valloc(4096); FILE *f = fopen("test.bin", "rb"); fread(blob, 1, 4096, f); fclose(f); unsigned offs = *(unsigned*)blob; f1 = (f1_t)(blob + offs); mprotect(blob, 4096, PROT_READ | PROT_WRITE | PROT_EXEC); char txt[] = "¡hello world!"; char txt2[sizeof(txt)] = ""; f1(txt, txt2, sizeof(txt) - 1); printf("%s\n%s\n", txt, txt2); return 0; } </code></pre>
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    1. CO`_GLOBAL_OFFSET_TABLE_` is probably needed if reference to other symbols (such as a standard library) are made.
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    2. CO@AProgrammer: But the OP specifically says _no external dependency_, so it is probably not needed. If he does access to any library then he will have to statically link all the libraries in the blob or do the dynamic linking himself... and that would be... complicated.
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