Re: Bug#539378: [hppa]: fails to load nfs module: Global Offset Table
On 08/01/2009 01:38 AM, Kyle McMartin wrote:
On Fri, Jul 31, 2009 at 06:00:48PM -0400, Carlos O'Donell wrote:
On Fri, Jul 31, 2009 at 5:26 PM, John David
Anglin<dave@hiauly1.hia.nrc.ca> wrote:
I don't have more details... The idea is as Carlos outlined. There's
code in the binutils elf32-hppa.c and elf64-hppa.c files to implement
the above for dynamic libraries. That's what made me think of it.
Binutils is not involved in the kernel module loader, instead
arch/parisc/kernel/module.c (get_fdesc) chooses where the gp will
point to.
If you set gp to the middle of the GOT table, *and* implement
long/short ldd access on 64-bit, then you would get a total of 8191
possible slots per module.
Personally I think the lower risk, quicker fix, is to implement a fix
for 64-bit kernels that uses ldd in format 3 for all offsets> 15
bytes, and thus allow you to set MAX_GOTS to 4095.
Note: ldd format 3 can't be used to load immediate values between 15
and -16 bytes.
Is it as simple as:
diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index ef5caf2..0502fab 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -82,13 +82,6 @@
return -ENOEXEC; \
}
-/* Maximum number of GOT entries. We use a long displacement ldd from
- * the bottom of the table, which has a maximum signed displacement of
- * 0x3fff; however, since we're only going forward, this becomes
- * 0x1fff, and thus, since each GOT entry is 8 bytes long we can have
- * at most 1023 entries */
-#define MAX_GOTS 1023
-
/* three functions to determine where in the module core
* or init pieces the location is */
static inline int in_init(struct module *me, void *loc)
@@ -126,6 +119,14 @@ struct stub_entry {
};
#endif
+/* Maximum number of GOT entries. We use a long displacement ldd from
+ * the bottom of the table, which has 16-bit signed displacement from
+ * %dp. Because we only use the forward direction, we're limited to
+ * 15-bits - 1, and because each GOT entry is 8-bytes wide, we're limited
+ * to 4095 entries.
+ */
+#define MAX_GOTS (((1<< 15) - 1) / sizeof(struct got_entry))
+
/* Field selection types defined by hppa */
#define rnd(x) (((x)+0x1000)&~0x1fff)
/* fsel: full 32 bits */
@@ -151,6 +152,15 @@ static inline int reassemble_14(int as14)
((as14& 0x2000)>> 13));
}
+/* Unusual 16-bit encoding, for wide mode only. */
+static inline int reassemble_16a(int as16)
+{
+ int s, t;
+ t = (as16<< 1)& 0xffff;
+ s = (as16& 0x8000);
+ return (t ^ s ^ (s>> 1)) | (s>> 15);
+}
+
static inline int reassemble_17(int as17)
{
return (((as17& 0x10000)>> 16) |
@@ -460,12 +470,16 @@ static Elf_Addr get_stub(struct module *me, unsigned long value, long addend,
*/
switch (stub_type) {
case ELF_STUB_GOT:
+ unsigned int d = get_got(me, value, addend)& 0x7fff;
+
stub->insns[0] = 0x537b0000; /* ldd 0(%dp),%dp */
stub->insns[1] = 0x53610020; /* ldd 10(%dp),%r1 */
stub->insns[2] = 0xe820d000; /* bve (%r1) */
stub->insns[3] = 0x537b0030; /* ldd 18(%dp),%dp */
- stub->insns[0] |= reassemble_14(get_got(me, value, addend)& 0x3fff);
+ if (d> 15)
+ stub->insns[0] |= reassemble_16a(d);
+
break;
case ELF_STUB_MILLI:
stub->insns[0] = 0x20200000; /* ldil 0,%r1 */
I don't think we need to worry about the initial 15-bytes displacement,
since they're all within the first got_entry? (The resulting assembly
looks alright from a 64-bit toolchain:
kyle@shortfin ~ $ cat foo.S
.text
a:
ldd 32760(%r27),%r27
break 0,0
0000000000000000<a>:
0: 53 7b ff f0 ldd 7ff8(dp),dp
int main(void) {
unsigned int opcode = 0x537b0000;
opcode |= re_assemble_16(32760);
printf("0x%x\n", opcode);
return 0;
}
kyle@shortfin ~ $ ./foo
0x537bfff0
Looks pretty happy?
Kyle, you beat me.
Attached is my patch ....
Tested and works.
root@c3000:~# uname -a
Linux c3000 2.6.31-rc4-64bit #42 SMP Sat Aug 1 01:37:29 CEST 2009 parisc64 GNU/Linux
root@c3000:~# lsmod
Module Size Used by
ipv6 493320 70
reiserfs 461624 0
nfs 300704 0
lockd 144456 1 nfs
nfs_acl 5592 1 nfs
sunrpc 382312 3 nfs,lockd,nfs_acl
msdos 15032 0
fat 91248 1 msdos
Helge
parisc: module.c - fix GOT table overflow with large kernel modules on 64 bit kernels
Signed-off-by: Helge Deller <deller@gmx.de>
diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
index ef5caf2..d280219 100644
--- a/arch/parisc/kernel/module.c
+++ b/arch/parisc/kernel/module.c
@@ -86,8 +86,12 @@
* the bottom of the table, which has a maximum signed displacement of
* 0x3fff; however, since we're only going forward, this becomes
* 0x1fff, and thus, since each GOT entry is 8 bytes long we can have
- * at most 1023 entries */
-#define MAX_GOTS 1023
+ * at most 1023 entries.
+ * To overcome this 14bit displacement with some kernel modules, we'll
+ * use instead the unusal 16bit displacement method (see reassemble_16a)
+ * which gives us a maximum positive displacement of 0x7fff, and as such
+ * allows us to allocate up to 4095 GOT entries. */
+#define MAX_GOTS 4095
/* three functions to determine where in the module core
* or init pieces the location is */
@@ -151,6 +155,17 @@ static inline int reassemble_14(int as14)
((as14 & 0x2000) >> 13));
}
+static inline int reassemble_16a(int as16)
+{
+ int s, t;
+
+ /* Unusual 16-bit encoding, for wide mode only. */
+ t = (as16 << 1) & 0xffff;
+ s = (as16 & 0x8000);
+ return (t ^ s ^ (s >> 1)) | (s >> 15);
+}
+
+
static inline int reassemble_17(int as17)
{
return (((as17 & 0x10000) >> 16) |
@@ -407,6 +422,7 @@ static Elf_Addr get_stub(struct module *me, unsigned long value, long addend,
enum elf_stub_type stub_type, Elf_Addr loc0, unsigned int targetsec)
{
struct stub_entry *stub;
+ int d;
/* initialize stub_offset to point in front of the section */
if (!me->arch.section[targetsec].stub_offset) {
@@ -460,12 +476,17 @@ static Elf_Addr get_stub(struct module *me, unsigned long value, long addend,
*/
switch (stub_type) {
case ELF_STUB_GOT:
- stub->insns[0] = 0x537b0000; /* ldd 0(%dp),%dp */
+ stub->insns[0] = 0x537b0000; /* ldd 0(%dp),%dp */
stub->insns[1] = 0x53610020; /* ldd 10(%dp),%r1 */
stub->insns[2] = 0xe820d000; /* bve (%r1) */
stub->insns[3] = 0x537b0030; /* ldd 18(%dp),%dp */
- stub->insns[0] |= reassemble_14(get_got(me, value, addend) & 0x3fff);
+ d = get_got(me, value, addend);
+ if (d <= 15)
+ stub->insns[0] |= reassemble_14(d);
+ else
+ stub->insns[0] |= reassemble_16a(d);
+
break;
case ELF_STUB_MILLI:
stub->insns[0] = 0x20200000; /* ldil 0,%r1 */
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