From 2eda7f11000646909a10298951c9defb2321b240 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Fri, 18 Dec 2020 22:16:19 +1100 Subject: 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 " Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201218111619.1206391-3-mpe@ellerman.id.au --- arch/powerpc/include/asm/ppc_asm.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'arch/powerpc/include/asm/ppc_asm.h') 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) -- cgit v1.2.3-59-g8ed1b