The context established by "makecontext" has a link register pointing
back to an error path within the makecontext routine. This is currently
covered by the CFI FDE for makecontext itself, which is simply wrong
for the stack frame *inside* the context. When trying to unwind (e.g.
doing a backtrace) in a routine inside a context created by makecontext,
this can lead to uninitialized stack slots being accessed, causing the
unwinder to crash in the worst case.
Similarly, during parts of the "setcontext" routine, when the stack
pointer has already been switched to point to the new context, the
address range is still covered by the CFI FDE for setcontext. When
trying to unwind in that situation (e.g. backtrace from an async
signal handler for profiling), it is again possible that the unwinder
crashes.
Theses are all problems in existing code, but the changes in stack
frame layout appear to make the "worst case" much more likely in
the ELFv2 ABI context. This causes regressions e.g. in the libgo
testsuite on ELFv2.
This patch fixes this by ending the makecontext/setcontext FDEs
before those problematic parts of the assembler, similar to what
is already done on other platforms. This fixes the libgo
regression on ELFv2.
http://sourceware.org/ml/libc-alpha/2013-08/msg00092.html
Use conditional form of branch and link to avoid destroying the cpu
link stack used to predict blr return addresses.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S: Use
conditional form of branch and link when obtaining pc.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S: Likewise.
2004-01-14 Steven Munroe <sjmunroe@us.ibm.com>
* include/libc-symbols.h [HAVE_ASM_GLOBAL_DOT_NAME]
(_symbol_version): Use C_SYMBOL_DOT_NAME to create '.'ed symbols.
(_default_symbol_version): Use C_SYMBOL_DOT_NAME to create '.'ed
symbols.
* sysdeps/powerpc/Makefile: Add rtld-global-offsets.sym to
gen-as-const-headers.
* sysdeps/powerpc/elf/rtld-global-offsets.sym: New file.
* sysdeps/powerpc/sysdep.h: Define v# symbols for vector registers.
Define PPC_FEATURE_* masks for Aux Vector AT_HWCAP.
* sysdeps/unix/sysv/linux/kernel-features.h
(__ASSUME_SWAPCONTEXT_SYSCALL): Define for PPC and 2.6.0 kernels.
* sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h [!__WORDSIZE == 32]:
Declare mcontext_t inline and include altivec state for 64-bit.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/Versions: Add GLIBC_2.3.4
versions for setcontext, getcontext, and swapcontext.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/Versions: Add GLIBC_2.3.4
versions for setcontext, getcontext, swapcontext, and makecontext.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/getcontext.S
(__getcontext): Upgrade to save Altivec regs and version GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3, GLIBC_2_3_4)](__novec_getcontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S
(__makecontext): Use parm save area instead of compiler_dw to hold
context pointer.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S
(__setcontext): Upgrade to restore Altivec regs and version
GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3, GLIBC_2_3_4)](__novec_setcontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/swapcontext.S
(__swapcontext): Upgrade to swap Altivec regs and version GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3, GLIBC_2_3_4)](__novec_swapcontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/ucontext_i.h
(SIGCONTEXT_V_REGS_PTR, SIGCONTEXT_V_RESERVE): Defined.
2004-01-12 Steven Munroe <sjmunroe@us.ibm.com>
* sysdeps/unix/sysv/linux/powerpc/powerpc32/Versions: Add GLIBC_2.3.4
versions for setcontext, getcontext, swapcontext, and makecontext.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S
(__getcontext): Upgrade to save Altivec regs and version GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3_3, GLIBC_2_3_4)](__novec_getcontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S
(__makecontext): Upgrade to align for Altivec regs and version
GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3_3, GLIBC_2_3_4)](__novec_makecontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S
(__setcontext): Upgrade to restore Altivec regs and version
GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3_3, GLIBC_2_3_4)](__novec_setcontext):
Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S
(__swapcontext): Upgrade to swap Altivec regs and version GLIBC_2_3_4.
[SHLIB_COMPAT (libc, GLIBC_2_3_3, GLIBC_2_3_4)]
(__novec_swapcontext): Compatible with GLIBC_2.3.3 release.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/ucontext_i.h:
(_UC_VSCR, _UC_VRSAVE): Define.
(_FRAME_BACKCHAIN, _FRAME_LR_SAVE,_FRAME_PARM_SAVE1,_FRAME_PARM_SAVE2,
_FRAME_PARM_SAVE3, _FRAME_PARM_SAVE4): Defined.
