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PowerPC: Fix vDSO missing ODP entries

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This patch fixes the vDSO symbol used directed in IFUNC resolver where
they do not have an associated ODP entry leading to undefined behavior
in some cases. It adds an artificial OPD static entry to such cases
and set its TOC to non 0 to avoid triggering lazy resolutions.
This commit is contained in:
Adhemerval Zanella 2013-11-07 05:34:22 -06:00
parent e4368156e6
commit 76a9b99861
4 changed files with 35 additions and 5 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2013-11-08 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
* sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h (VDSO_IFUNC_RET):
Add artificial ODP entry for vDSO symbol for PPC64.
* sysdeps/unix/sysv/linux/powerpc/gettimeofday.c: Adjust includes.
* sysdeps/unix/sysv/linux/powerpc/time.c: Likewise.
2013-11-07 Ondřej Bílka <neleai@seznam.cz>
[BZ #15374]

30
sysdeps/unix/sysv/linux/powerpc/bits/libc-vdso.h
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@ -41,12 +41,32 @@ extern void *__vdso_sigtramp32;
extern void *__vdso_sigtramp_rt32;
#endif
/* This macro is needed for PPC64 to return a skeleton OPD entry of a vDSO
symbol. This works because _dl_vdso_vsym always return the function
address, and no vDSO symbols use the TOC or chain pointers from the OPD
so we can allow them to be garbage. */
#if defined(__PPC64__) || defined(__powerpc64__)
#define VDSO_IFUNC_RET(value) ((void *) &(value))
/* The correct solution is for _dl_vdso_vsym to return the address of the OPD
for the kernel VDSO function. That address would then be stored in the
__vdso_* variables and returned as the result of the IFUNC resolver function.
Yet, the kernel does not contain any OPD entries for the VDSO functions
(incomplete implementation). However, PLT relocations for IFUNCs still expect
the address of an OPD to be returned from the IFUNC resolver function (since
PLT entries on PPC64 are just copies of OPDs). The solution for now is to
create an artificial static OPD for each VDSO function returned by a resolver
function. The TOC value is set to a non-zero value to avoid triggering lazy
symbol resolution via .glink0/.plt0 for a zero TOC (requires thread-safe PLT
sequences) when the dynamic linker isn't prepared for it e.g. RTLD_NOW. None
of the kernel VDSO routines use the TOC or AUX values so any non-zero value
will work. Note that function pointer comparisons will not use this artificial
static OPD since those are resolved via ADDR64 relocations and will point at
the non-IFUNC default OPD for the symbol. Lastly, because the IFUNC relocations
are processed immediately at startup the resolver functions and this code need
not be thread-safe, but if the caller writes to a PLT slot it must do so in a
thread-safe manner with all the required barriers. */
#define VDSO_IFUNC_RET(value) \
({ \
static Elf64_FuncDesc vdso_opd = { .fd_toc = ~0x0 }; \
vdso_opd.fd_func = (Elf64_Addr)value; \
&vdso_opd; \
})
#else
#define VDSO_IFUNC_RET(value) ((void *) (value))
#endif

1
sysdeps/unix/sysv/linux/powerpc/gettimeofday.c
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@ -22,6 +22,7 @@
# include <dl-vdso.h>
# include <bits/libc-vdso.h>
# include <dl-machine.h>
void *gettimeofday_ifunc (void) __asm__ ("__gettimeofday");

2
sysdeps/unix/sysv/linux/powerpc/time.c
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@ -20,7 +20,9 @@
# include <time.h>
# include <sysdep.h>
# include <dl-vdso.h>
# include <bits/libc-vdso.h>
# include <dl-machine.h>
void *time_ifunc (void) asm ("time");