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From the point of view of GDB's core, the patch below may be closer to correct than you think (don't know how well it fits into the definition of the debug info - debug maintainer problem :-).Hi, Bug 567 complains that when you build gdb for sparc-sun-solaris2.8 as a 64-bit program, then when you use it to debug a 32-bit program things happen like: (gdb) p d1 Cannot access memory at address 0xffbef7a0 (gdb) x/fg &d1 0xffbef7a0: 3.2999999999999998 (Actually 567 shows the wrong value being printed to x/fg, but this seems to be fixed at gcc-3.2 / gdb 5.2.1). It turns out that you can't "p" any kind of variable: the problem isn't limited to double. The problem seemed to me that 32-bit negative stack offsets became +ve 64-bit quantities. This would give a 33-bit address (the wanted address with an extra "1" on the left). Ideally, I think gdb should just mask off the extra bit when debugging 32-bit code. But I couldn't figure out how to do that, so the attached patch sign-extends symbol values as they are read in.
GCC 3.2 configuration:
/tmp/gcc-3.2/configure --prefix=/usr/local/gcc-3.2
GDB 5.2.1 configuration
PATH=/usr/local/gcc-3.2/bin:$PATH
export PATH
CC="gcc -m64"
export CC
CFLAGS="-g -O2"
export CFLAGS
./configure --prefix=/usr/local/solaris2.8_64
You need to put "-m64" in CC rather than CFLAGS else "make install" fails when
trying to build "chew". This has the unfortunate side-effect that "make check"
also uses "gcc -m64", i.e. it never exercises "gcc" which would build a 32-bit
program.
Cheers ... Duncan.
diff -r -u gdb-5.2.1.bu/gdb/dbxread.c gdb-5.2.1/gdb/dbxread.c
--- gdb-5.2.1.bu/gdb/dbxread.c Fri Apr 5 08:33:49 2002
+++ gdb-5.2.1/gdb/dbxread.c Thu Nov 14 16:23:40 2002
@@ -2591,6 +2591,27 @@
fill_symbuf (abfd);
bufp = &symbuf[symbuf_idx++];
INTERNALIZE_SYMBOL (nlist, bufp, abfd);
+
+ /* ----------------------------------------------- */
+ /* Horrible fix for when gdb is built with "-m64" */
+ /* (sparc-sun-solaris2.8): */
+ /* sign-extend the 32-bit result in nlist.n_value. */
+ /* */
+ /* This fixes the testcase in bug 567, */
+ /* in that you can "p d1" successfully. */
+ /* Actually you can "p" *anything* */
+ /* (previously, you couldn't). */
+ /* */
+ /* I expect this will break something else, */
+ /* we'll just have to wait to see what. */
+ /* */
+ /* The proper fix is for gdb to know that it's */
+ /* working on a 32-bit program and */
+ /* truncate addresses to 32 bits before using them */
+ /* ----------------------------------------------- */
+ + nlist.n_value = (long)(int)nlist.n_value;
+ OBJSTAT (objfile, n_stabs++);
type = bfd_h_get_8 (abfd, bufp->e_type);
/*
* From GDB bug report 567
gcc -g -m64 -o double double.c
gcc -g -o double double.c
*
* The report says to breakpoint on the printf line
* & print the value of d1
*/
extern int printf(const char *, ...);
int
main()
{
double d1;
d1 = 3.3;
printf("d1 = %f\n", d1);
return 0;
}
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