[V21.4] "clever" compilers sometimes opt away too much.

Steve Youngs <steve(a)sxemacs.org&gt; writes: > Sorry, haven't checked 21.5, but I'd imagine this is needed there > too. > > 21.4 patch: > ChangeLog files diff command: cvs -q diff -U 0 > Files affected: src/ChangeLog > Source files diff command: cvs -q diff -uN > Files affected: src/emacs.c > > Index: src/ChangeLog > =================================================================== > RCS file: /pack/xemacscvs/XEmacs/xemacs/src/ChangeLog,v > retrieving revision 1.290.2.83 > diff -u -U0 -r1.290.2.83 ChangeLog > --- src/ChangeLog 11 Jan 2005 02:02:11 -0000 1.290.2.83 > +++ src/ChangeLog 12 Jan 2005 01:11:36 -0000 > ＠＠ -0,0 +1,7 ＠＠ > +2005-01-12 Steve Youngs <steve(a)sxemacs.org&gt; > + > + From Evgeny Zajcev <lg(a)sxemacs.org&gt;: > + > + * emacs.c (debug_can_access_memory): Fix problem of "clever" > + compilers being over-zealous in their optimising. > + > Index: src/emacs.c > =================================================================== > RCS file: /pack/xemacscvs/XEmacs/xemacs/src/emacs.c,v > retrieving revision 1.97.2.8 > diff -u -u -r1.97.2.8 emacs.c > --- src/emacs.c 13 Jun 2004 20:19:39 -0000 1.97.2.8 > +++ src/emacs.c 12 Jan 2005 01:10:26 -0000 > ＠＠ -535,15 +535,13 ＠＠ > old_sigsegv = > (SIGTYPE (*) (int)) signal (SIGSEGV, debug_memory_error); > > - if (len > 1) > - /* If we can, try to avoid problems with super-optimizing compilers > - that might decide that memcmp (ptr, ptr, len) can be optimized > - away since its result is always 1. */ > - memcmp (ptr, (char *) ptr + 1, len - 1); > - else > - memcmp (ptr, ptr, len); > - } > - else > + /* Examine memory pool at PTR */ > + while (len-- > 0) { > + char a = ((char*)ptr)[len]; > + if (a == '1') > + /* pass */; > + } > + } else > retval = 0; > signal (SIGBUS, old_sigbus); > signal (SIGSEGV, old_sigsegv); This patch should look like this (to work with gcc295 and gcc342): Index: src/ChangeLog =================================================================== RCS file: /pack/xemacscvs/XEmacs/xemacs/src/ChangeLog,v retrieving revision 1.290.2.83 diff -u -U0 -r1.290.2.83 ChangeLog --- src/ChangeLog 11 Jan 2005 02:02:11 -0000 1.290.2.83 +++ src/ChangeLog 12 Jan 2005 01:11:36 -0000 ＠＠ -0,0 +1,7 ＠＠ +2005-01-12 Steve Youngs <steve(a)sxemacs.org&gt; + + From Evgeny Zajcev <lg(a)sxemacs.org&gt;: + + * emacs.c (debug_can_access_memory): Fix problem of "clever" + compilers being over-zealous in their optimising. + Index: src/emacs.c =================================================================== RCS file: /pack/xemacscvs/XEmacs/xemacs/src/emacs.c,v retrieving revision 1.97.2.8 diff -u -u -r1.97.2.8 emacs.c --- src/emacs.c 13 Jun 2004 20:19:39 -0000 1.97.2.8 +++ src/emacs.c 12 Jan 2005 01:10:26 -0000 ＠＠ -535,15 +535,13 ＠＠ old_sigsegv = (SIGTYPE (*) (int)) signal (SIGSEGV, debug_memory_error); - if (len > 1) - /* If we can, try to avoid problems with super-optimizing compilers - that might decide that memcmp (ptr, ptr, len) can be optimized - away since its result is always 1. */ - memcmp (ptr, (char *) ptr + 1, len - 1); - else - memcmp (ptr, ptr, len); - } - else + /* Examine memory pool at PTR */ + while (len-- > 0) { + char a = ((char*)ptr)[len]; + if (a == '1') + ((char*)ptr)[len] = a; + } + } else retval = 0; signal (SIGBUS, old_sigbus); signal (SIGSEGV, old_sigsegv); -- lg