Help with confusing C code in loader?
dillon at apollo.backplane.com
Sun Jul 29 17:43:26 PDT 2007
:I'm trying to debug a problem in /boot/loader but I'm stumped by
:this line in sys/boot/common/module.c:
:error = (file_formats[i]->l_load)(filename, loadaddr, &fp);
:This seems to refer to a line in common/bootstrap.h:
:int (* l_load)(char *filename, u_int64_t dest, struct preloaded_file **result);
:And that's where I lose the thread. I can't figure out what the
:(* l_load) means because 'l_load' doesn't seem to be defined in
:any obvious place.
:Any clues most welcome.
extern struct file_format *file_formats;
file_formats is an array of pointers to a structure. Each supported
file format has its own structure.
The file_format structure is defined somewhere, not sure. But the
jist is that each individual format supported creates a file_format
structure, e.g. /usr/src/sys/boot/pc32/libi386/elf32_freebsd.c line
44. A pointer to the structure is installed in the file_formats
array so the loader can iterate through the various load formats
The actual function being called is supplied by the individual
loaders (see same file above, a pointer to elf32_loadfile() is
loaded into the file_format structure). The code you are
referencing is what calls through to that function.
The l_load declration you found is not specifically related.
<dillon at backplane.com>
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