Can I link a plain file into my executable? [duplicate]
Some frameworks (Qt, Windows, Gtk...) offer functionality to add resources to your binaries. I wonder if it would be possible to achieve this without the framework, since all that is really needed is
- a symbol to contain the resource's address within the binary (data segment)
- a symbol to represent the length of the resource
- the resource itself
How can this be achieved with the gcc toolchain?
Solution 1:
You could do this:
objcopy --input binary \
--output elf32-i386 \
--binary-architecture i386 my_file.xml myfile.o
This produces an object file that you can link into your executable. This file will contain these symbols that you'll have to declare in your C code to be able to use them
00000550 D _binary_my_file_xml_end
00000550 A _binary_my_file_xml_size
00000000 D _binary_my_file_xml_start
Solution 2:
At its most basic, the equivalent is a char
array full of bytes.
On Linux you can use xxd -i <file>
to "compile" files into char
arrays, then link the arrays into your binary and use the constituent bytes however you please.
Here's an example from my own code's makefile
, that creates a "resource file" called templates.h
containing a bunch of char
arrays representing HTML templates:
templates.h:
@echo "#ifndef REDACTED_TEMPLATES_H" > templates.h
@echo "#define REDACTED_TEMPLATES_H" >> templates.h
@echo "// Auto-generated file! Do not modify!" >> templates.h
@echo "// NB: arrays are not null-terminated" >> templates.h
@echo "// (anonymous namespace used to force internal linkage)" >> templates.h
@echo "namespace {" >> templates.h
@echo "namespace templates {" >> templates.h
@cd templates;\
for i in * ;\
do \
echo "Compiling $$i...";\
xxd -i $$i | sed -e 's/ =/ __attribute__((unused)) =/' >> ../templates.h;\
done;\
cd ..
@echo "}" >> templates.h
@echo "}" >> templates.h
@echo "#endif" >> templates.h
(see also: How best can I programmatically apply `__attribute__ ((unused))` to these auto-generated objects?)
The result looks a little like:
#ifndef REDACTED_TEMPLATES_H
#define REDACTED_TEMPLATES_H
// Auto-generated file! Do not modify!
// NB: arrays are not null-terminated
// (anonymous namespace used to force internal linkage)
namespace {
namespace templates {
unsigned char alert_email_finished_events_html[] __attribute__((unused)) = {
0x3c, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x20, 0x63, 0x6c, 0x61, 0x73, 0x73,
0x3d, 0x22, 0x6e, 0x6f, 0x64, 0x65, 0x2d, 0x69, 0x6e, 0x66, 0x6f, 0x2d,
[..]
0x7d, 0x7d, 0x0d, 0x0a, 0x3c, 0x2f, 0x74, 0x61, 0x62, 0x6c, 0x65, 0x3e,
0x0d, 0x0a
};
unsigned int alert_email_finished_events_html_len __attribute__((unused)) = 290;
unsigned char alert_email_finished_events_list_html[] __attribute__((unused)) = {
0x3c, 0x74, 0x72, 0x20, 0x63, 0x6c, 0x61, 0x73, 0x73, 0x3d, 0x22, 0x73,
0x65, 0x70, 0x61, 0x72, 0x61, 0x74, 0x65, 0x2d, 0x70, 0x72, 0x65, 0x76,
[..]
0x73, 0x74, 0x7d, 0x7d, 0x0d, 0x0a
};
unsigned int alert_email_finished_events_list_html_len __attribute__((unused)) = 42;
}
}
#endif
Note that this particular example is optimal when using the resource in only one Translation Unit, but the general approach can be adapted to suit your needs.