tag 381452 patch
thanks
This is a very ugly misdesign in the emacs core. It uses the upper 4
bits of an elisp object pointer for type information. These 4 bits
are restored by dereferencing the pointer by ORing it with a
well-known platform specific value, 0x10000000 on mips.
The .data section indeed used to start after 0x10000000 with binutils
up to 2.16. In binutils 2.17, the ld scripts were modified, and the
.data section will start after .text, without a gap (around 0x004a0000
in my test cases). Emacs, however, still ORed the pointer with
0x10000000 without checking the facts, and the dereferenced pointer
was 0x104a0000 which is invalid, and instantly led to a segmentation
fault.
I had several ideas to fix this, e.g. setting the OR value to 0, which
worked well with binutils 2.17, but would crash with older binutils.
I ended up with patching the linker script to restore the old
behaviour. See my patch.
--- src/m/mips.h.orig 2006-09-18 13:12:35.557829500 +0200
+++ src/m/mips.h 2006-09-18 13:12:37.165930000 +0200
@@ -142,6 +142,12 @@
/* Alter some of the options used when linking. */
+#ifdef THIS_IS_MAKEFILE
+#define LD_SWITCH_MACHINE -T "../../mips.ld"
+#else
+#define LD_SWITCH_MACHINE -T "../mips.ld"
+#endif
+
#if !defined(NEWSOS5) && !defined(__linux__)
#ifdef BSD_SYSTEM
--- /dev/null 2006-09-14 13:24:19.000000000 +0200
+++ debian/mips.ld 2006-09-18 13:12:42.178243250 +0200
@@ -0,0 +1,244 @@
+/* Work around a design flaw in emacs: emacs assumes the data section
+begins on address 0x10000000, which was true up to binutils version
+2.16, but the binutils 2.17 default linker script does not use this
+alignment anymore.
+
+This is actually a patched version of the file
+/usr/lib/ldscripts/elf32btsmip.x from binutils 2.17-2. It makes the
+data section begin at 0x10000000.
+
+- 2006/09/17 Max Kellermann <[EMAIL PROTECTED]> */
+
+/* Default linker script, for normal executables */
+OUTPUT_FORMAT("elf32-tradbigmips", "elf32-tradbigmips",
+ "elf32-tradlittlemips")
+OUTPUT_ARCH(mips)
+ENTRY(__start)
+SEARCH_DIR("/usr/mips-linux-gnu/lib"); SEARCH_DIR("/usr/local/lib");
SEARCH_DIR("/lib"); SEARCH_DIR("/usr/lib");
+SECTIONS
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