Patch for bug 567 (sparc-sun-solaris2.8)

Duncan Roe
2002-11-15T04:37:03Z

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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.

[-- Attachment #2: The patch --]
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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);

[-- Attachment #3: (simplified) test program from bug 567 --]
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/*
* 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;
}