[POWERPC] Ensure FULL_REGS on exec
When PTRACE_O_TRACEEXEC is used, a ptrace call to fetch the registers at the PTRACE_EVENT_EXEC stop (PTRACE_PEEKUSR) will oops in CHECK_FULL_REGS. With recent versions, "gdb --args /bin/sh -c 'exec /bin/true'" and "run" at the (gdb) prompt is sufficient to produce this. I also have written an isolated test case, see https://bugzilla.redhat.com/show_bug.cgi?id=301791#c15. This change fixes the problem by clearing the low bit of pt_regs.trap in start_thread so that FULL_REGS is true again. This is correct since all of the GPRs that "full" refers to are cleared in start_thread. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Paul Mackerras <paulus@samba.org>
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@ -605,6 +605,13 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
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regs->ccr = 0;
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regs->gpr[1] = sp;
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/*
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* We have just cleared all the nonvolatile GPRs, so make
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* FULL_REGS(regs) return true. This is necessary to allow
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* ptrace to examine the thread immediately after exec.
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*/
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regs->trap &= ~1UL;
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#ifdef CONFIG_PPC32
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regs->mq = 0;
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regs->nip = start;
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