Date: Thu, 21 Mar 2002 21:50:24 -0500 From: Garance A Drosihn <drosih@rpi.edu> To: phk@FreeBSD.ORG Cc: hackers@FreeBSD.ORG Subject: Re: C-struct dismantling tool... Message-ID: <p05101521b8c0338befde@[128.113.24.47]> In-Reply-To: <Pine.BSF.4.21.0203211256570.17693-100000@InterJet.elischer.org> References: <Pine.BSF.4.21.0203211256570.17693-100000@InterJet.elischer.org>
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At 12:57 PM -0800 3/21/02, Julian Elischer wrote:
>On Thu, 21 Mar 2002, John Polstra wrote:
>
>>
>> I thought about the .stabs approach too, and thought it seemed
> > promising. Even better might be to use -gdwarf -g3, which in
> > theory at least would provide information about #defines.
> >
> > For well-behaved structs, it's possible that rpcgen could be
> > hacked up to do what you want.
>
>Sounds like a job for an objdump mutant.
Or write a C-program which prints offset(x) and sizeof(x) for
each field in the struct. It might not be too hard to write
a perl or ruby script which could generate such a program for
a given struct+include file. Here's a quick & dirty example.
Perhaps someone C-smarter than I am could figure out how to
reliably add a column indicating if the variable is signed or
unsigned, integer or floating-point, plus any other interesting
characteristics. The "tricky" lines below are only "tricky" in
the sense that it would be tricky to get a script to *know* to
add the lines for those fields, such they are a sub-structure.
With a little more thought, it could also map out the struct,
indicating any bytes which were skipped over. Though it seems
to me there should be some way to get the compiler itself to
dump out something like this. I know I have seen that in some
non-C compilers, and I thought I had also seen it in some C
compilers...
/*
* Grungy little program to print out a stat structure.
* Garance/Mar 21/2002
*
* cc -Wall -o dumpstat.o dumpstat.c
*/
#include <sys/stat.h>
#include <stddef.h>
#include <stdio.h>
#define showheader(xStruct) {\
printf("Dump of '%s':\n", #xStruct);\
printf(" offset size fieldname\n");\
}
#define showfield(xStruct,xVar) {\
indent = 1; \
for (cp = #xVar; *cp != '\0'; cp++) \
if (*cp == '.') indent += 2;\
printf(" 0x%04lX %4lu%*s- %-1s\n", \
(unsigned long) offsetof(xStruct, xVar), \
(unsigned long) sizeof(((xStruct *)0)->xVar), \
indent, " ", #xVar);\
}
#define showtotal(xStruct) {\
printf("Total size = 0x%04lX aka %lu bytes)\n", \
(unsigned long) sizeof(xStruct), \
(unsigned long) sizeof(xStruct));\
}
int
main(int argc, char **argv)
{
const char *cp;
int indent;
showheader(struct stat);
showfield(struct stat, st_dev);
showfield(struct stat, st_ino);
showfield(struct stat, st_mode);
showfield(struct stat, st_nlink);
showfield(struct stat, st_uid);
showfield(struct stat, st_gid);
showfield(struct stat, st_rdev);
#ifndef _POSIX_SOURCE
showfield(struct stat, st_atimespec);
showfield(struct stat, st_atimespec.tv_sec); /* tricky */
showfield(struct stat, st_atimespec.tv_nsec); /* tricky */
showfield(struct stat, st_mtimespec);
showfield(struct stat, st_mtimespec.tv_sec); /* tricky */
showfield(struct stat, st_mtimespec.tv_nsec); /* tricky */
showfield(struct stat, st_ctimespec);
showfield(struct stat, st_ctimespec.tv_sec); /* tricky */
showfield(struct stat, st_ctimespec.tv_nsec); /* tricky */
#else
showfield(struct stat, st_atime);
showfield(struct stat, st_atimensec);
showfield(struct stat, st_mtime);
showfield(struct stat, st_mtimensec);
showfield(struct stat, st_ctime);
showfield(struct stat, st_ctimensec);
#endif
showfield(struct stat, st_size);
showfield(struct stat, st_blocks);
showfield(struct stat, st_blksize);
showfield(struct stat, st_flags);
showfield(struct stat, st_gen);
showfield(struct stat, st_qspare);
showtotal(struct stat);
return 0;
}
--
Garance Alistair Drosehn = gad@eclipse.acs.rpi.edu
Senior Systems Programmer or gad@freebsd.org
Rensselaer Polytechnic Institute or drosih@rpi.edu
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