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| author | Michael Ellerman <mpe@ellerman.id.au> | 2020-12-18 14:16:19 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-12-21 14:06:26 +0300 |
| commit | 2eda7f11000646909a10298951c9defb2321b240 (patch) | |
| tree | 1b33c970ed2c069a4955908a45d5fe5016e9f1c6 /arch/powerpc | |
| parent | 107521e8039688f7a9548f17919dfde670b911c1 (diff) | |
| download | linux-2eda7f11000646909a10298951c9defb2321b240.tar.xz | |
powerpc/vdso: Fix DOTSYM for 32-bit LE VDSO
Skirmisher reported on IRC that the 32-bit LE VDSO was hanging. This
turned out to be due to a branch to self in eg. __kernel_gettimeofday.
Looking at the disassembly with objdump -dR shows why:
00000528 <__kernel_gettimeofday>:
528: f0 ff 21 94 stwu r1,-16(r1)
52c: a6 02 08 7c mflr r0
530: f0 ff 21 94 stwu r1,-16(r1)
534: 14 00 01 90 stw r0,20(r1)
538: 05 00 9f 42 bcl 20,4*cr7+so,53c <__kernel_gettimeofday+0x14>
53c: a6 02 a8 7c mflr r5
540: ff ff a5 3c addis r5,r5,-1
544: c4 fa a5 38 addi r5,r5,-1340
548: f0 00 a5 38 addi r5,r5,240
54c: 01 00 00 48 bl 54c <__kernel_gettimeofday+0x24>
54c: R_PPC_REL24 .__c_kernel_gettimeofday
Because we don't process relocations for the VDSO, this branch remains
a branch from 0x54c to 0x54c.
With the preceding patch to prohibit R_PPC_REL24 relocations, we
instead get a build failure:
0000054c R_PPC_REL24 .__c_kernel_gettimeofday
00000598 R_PPC_REL24 .__c_kernel_clock_gettime
000005e4 R_PPC_REL24 .__c_kernel_clock_gettime64
00000630 R_PPC_REL24 .__c_kernel_clock_getres
0000067c R_PPC_REL24 .__c_kernel_time
arch/powerpc/kernel/vdso32/vdso32.so.dbg: dynamic relocations are not supported
The root cause is that we're branching to `.__c_kernel_gettimeofday`.
But this is 32-bit LE code, which doesn't use function descriptors, so
there are no dot symbols.
The reason we're trying to branch to a dot symbol is because we're
using the DOTSYM macro, but the ifdefs we use to define the DOTSYM
macro do not currently work for 32-bit LE.
So like previous commits we need to differentiate if the current
compilation unit is 64-bit, rather than the kernel as a whole. ie.
switch from CONFIG_PPC64 to __powerpc64__.
With that fixed 32-bit LE code gets the empty version of DOTSYM, which
just resolves to the original symbol name, leading to a direct branch
and no relocations:
000003f8 <__kernel_gettimeofday>:
3f8: f0 ff 21 94 stwu r1,-16(r1)
3fc: a6 02 08 7c mflr r0
400: f0 ff 21 94 stwu r1,-16(r1)
404: 14 00 01 90 stw r0,20(r1)
408: 05 00 9f 42 bcl 20,4*cr7+so,40c <__kernel_gettimeofday+0x14>
40c: a6 02 a8 7c mflr r5
410: ff ff a5 3c addis r5,r5,-1
414: f4 fb a5 38 addi r5,r5,-1036
418: f0 00 a5 38 addi r5,r5,240
41c: 85 06 00 48 bl aa0 <__c_kernel_gettimeofday>
Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.")
Reported-by: "Will Springer <skirmisher@protonmail.com>"
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201218111619.1206391-3-mpe@ellerman.id.au
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/include/asm/ppc_asm.h | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h index cfa814824285..cc1bca571332 100644 --- a/arch/powerpc/include/asm/ppc_asm.h +++ b/arch/powerpc/include/asm/ppc_asm.h @@ -180,7 +180,12 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR) #define VCPU_GPR(n) __VCPU_GPR(__REG_##n) #ifdef __KERNEL__ -#ifdef CONFIG_PPC64 + +/* + * We use __powerpc64__ here because we want the compat VDSO to use the 32-bit + * version below in the else case of the ifdef. + */ +#ifdef __powerpc64__ #define STACKFRAMESIZE 256 #define __STK_REG(i) (112 + ((i)-14)*8) |