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Revert "cputlb: Restrict SavedIOTLB to system emulation"

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This reverts commit d7ee93e243.

That commit tries to make a field in the CPUState struct not be
present when CONFIG_USER_ONLY is set.  Unfortunately, you can't
conditionally omit fields in structs like this based on ifdefs that
are set per-target.  If you try it, then code in files compiled
per-target (where CONFIG_USER_ONLY is or can be set) will disagree
about the struct layout with files that are compiled once-only (where
this kind of ifdef is never set).

This manifests specifically in 'make check-tcg' failing, because code
in cpus-common.c that sets up the CPUState::cpu_index field puts it
at a different offset from the code in plugins/core.c in
qemu_plugin_vcpu_init_hook() which reads the cpu_index field.  The
latter then hits an assert because from its point of view every
thread has a 0 cpu_index. There might be other weird behaviour too.

Mostly we catch this kind of bug because the CONFIG_whatever is
listed in include/exec/poison.h and so the reference to it in
build-once source files will then cause a compiler error.
Unfortunately CONFIG_USER_ONLY is an exception to that: we have some
places where we use it in "safe" ways in headers that will be seen by
once-only source files (e.g.  ifdeffing out function prototypes) and
it would be a lot of refactoring to be able to get to a position
where we could poison it.  This leaves us in a "you have to be
careful to walk around the bear trap" situation...

Fixes: d7ee93e243 ("cputlb: Restrict SavedIOTLB to system emulation")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230620175712.1331625-1-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Peter Maydell 2023-06-20 18:57:12 +01:00 committed by Richard Henderson
parent 2346098b95
commit c5ffd16ba4
1 changed files with 2 additions and 4 deletions
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6
include/hw/core/cpu.h
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@ -226,7 +226,7 @@ struct CPUWatchpoint {
QTAILQ_ENTRY(CPUWatchpoint) entry;
};
#if defined(CONFIG_PLUGIN) && !defined(CONFIG_USER_ONLY)
#ifdef CONFIG_PLUGIN
/*
* For plugins we sometime need to save the resolved iotlb data before
* the memory regions get moved around by io_writex.
@ -410,11 +410,9 @@ struct CPUState {
#ifdef CONFIG_PLUGIN
GArray *plugin_mem_cbs;
#if !defined(CONFIG_USER_ONLY)
/* saved iotlb data from io_writex */
SavedIOTLB saved_iotlb;
#endif /* !CONFIG_USER_ONLY */
#endif /* CONFIG_PLUGIN */
#endif
/* TODO Move common fields from CPUArchState here. */
int cpu_index;