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<d...@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:
k...@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;
}
k...@shortfin ~ $ ./foo
0x537bfff0
Looks pretty happy?
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