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

[Duncan Roe <duncanr@optimation.com.au>]

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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;
    }