On Fri, Aug 08, 2025 at 04:00:42PM +0200, Philippe Mathieu-Daudé wrote:
> Hi Markus,
>
> On 8/8/25 10:08, Markus Armbruster wrote:
> > tcg_region_init() calls one of qemu_mprotect_rwx(),
> > qemu_mprotect_rw(), and mprotect(), then reports failure with
> > error_setg_errno(&error_fatal, errno, ...).
> >
> > The use of &error_fatal is undesirable. qapi/error.h advises:
> >
> > * Please don't error_setg(&error_fatal, ...), use error_report() and
> > * exit(), because that's more obvious.
> >
> > The use of errno is wrong. qemu_mprotect_rwx() and qemu_mprotect_rw()
> > wrap around qemu_mprotect__osdep(). qemu_mprotect__osdep() calls
> > mprotect() on POSIX, VirtualProtect() on Windows, and reports failure
> > with error_report(). VirtualProtect() doesn't set errno. mprotect()
> > does, but error_report() may clobber it.
> >
> > Fix tcg_region_init() to report errors only when it calls mprotect(),
> > and rely on qemu_mprotect_rwx()'s and qemu_mprotect_rw()'s error
> > reporting otherwise. Use error_report(), not error_setg().
> >
> > Fixes: 22c6a9938f75 (tcg: Merge buffer protection and guard page protection)
> > Fixes: 6bc144237a85 (tcg: Use Error with alloc_code_gen_buffer)
> > Cc: Richard Henderson <richard.hender...@linaro.org>
> > Signed-off-by: Markus Armbruster <arm...@redhat.com>
> > ---
> > tcg/region.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/tcg/region.c b/tcg/region.c
> > index 7ea0b37a84..74e3b4b774 100644
> > --- a/tcg/region.c
> > +++ b/tcg/region.c
> > @@ -832,13 +832,17 @@ void tcg_region_init(size_t tb_size, int splitwx,
> > unsigned max_threads)
> > } else {
> > #ifdef CONFIG_POSIX
> > rc = mprotect(start, end - start, need_prot);
> > + if (rc) {
> > + error_report("mprotect of jit buffer: %s",
> > + strerror(errno));
> > + }
> > +
> > #else
> > g_assert_not_reached();
> > #endif
> > }
> > if (rc) {
> > - error_setg_errno(&error_fatal, errno,
> > - "mprotect of jit buffer");
> > + exit(1);
>
> - Before:
>
> Error displayed when qemu_mprotect_rwx/qemu_mprotect_rw/mprotect fail,
> then exit.
>
> - After:
>
> Error only displayed when mprotect() fails, then exit.
> Nothing displayed when qemu_mprotect_rwx() or qemu_mprotect_rw() failed,
> and exit.
Check the impl in qemu_mprotect__osdep - it calls error_report already,
so those code paths didn't need to be changedin this patch.
With regards,
Daniel
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