sutton@daemon.UUCP (Carl Sutton) (01/23/85)
Subject: ld sometimes a produces bad symbol table
Index: bin/ld.c 4.2BSD
Description:
If the loader (ld) is given an object file as argument with zero length
data *and* text sections, then the symbol table and the string table
will be written out incorrectly.
The loader, in the name of efficiency, detects input files without data
and text regions early in the first pass. A file name symbol is added
by the loader on the second pass. Since the symbol table allocation
necessary for local symbols is calculated on the first pass, the file
name symbol did not have space allocated for it in the symbol table.
Thus, the symbol table overruns its area in the output file and screws
up a couple of the string table entries. The string table size (stored
at the beginning of the string table) and the first string table entry
are typically over written.
Repeat-By:
#
# Create a file that produces no text and no data
#
# Example:
#
[1]% cat test.c
#define yes 1
struct nobody {
char however;
};
#
# Create a second file with data and/or text
# (just to make the problem easier to see)
#
# Example:
#
[2]% cat test1.c
static char *RCSid = "$Header";
#
# Compile the files without loading
#
[3]% cc -c -O test.c test1.c
test.c:
test1.c:
[4]% nm test.o
nm: test.o: no name list
[5]% nm test1.o
00000000 d _RCSid
#
# With the old loader
#
[6]% ld -r -M -o tout.o test.o test1.o
test.o
test1.o
[7]% nm tout.o
00000000 t
00000000 t
#
# Now, with the fixed loader
#
[8]% /bin/ld -r -M -o tout1.o test.o test1.o
test.o
test1.o
[9]% nm tout1.o
00000000 d _RCSid
00000000 t test.o
00000000 t test1.o
Fix:
Simply increment the symbol table allocation size when zero length data
and text sections are detected. See routine load1().
RCS file: RCS/ld.c,v
retrieving revision 1.2
retrieving revision 1.3
diff -r1.2 -r1.3
2c2
< static char *RCSid = "$Header: ld.c,v 1.2 84/12/11 17:03:26 sutton Exp $";
---
> static char *RCSid = "$Header: ld.c,v 1.3 85/01/21 14:22:14 sutton Exp $";
10a11,15
> * Revision 1.3 85/01/21 14:22:14 sutton
> * Fixed bug in load1() that did not allocate space
> * for a file name symbol if filhdr.a_text and filhdr.a_data
> * both equaled zero.
> *
796c801,810
< if (filhdr.a_text+filhdr.a_data == 0)
---
> if (filhdr.a_text+filhdr.a_data == 0) {
> /*
> * ssize must be incremented here.
> * On the second pass, the loader
> * inserts a symbol in the symbol
> * table for each object file whether
> * the file contributes to the final
> * object or not.
> */
> ssize += sizeof(cursym);
797a812
> }