Message ID | 1456808869-20286-1-git-send-email-sw@weilnetz.de (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
> From: Stefan Weil [mailto:sw@weilnetz.de] > Sent: Monday, 29 February 2016 9:08 PM > > The rest of the code can use longjmp with stack unwinding. > > Signed-off-by: Stefan Weil <sw@weilnetz.de> > --- > > This is a bug fix needed for 64 bit Windows. > > QEMU for Windows currently gets the wrong definition for > sigsetjmp. It uses stack unwinding for longjmp which results > in a crash when it is called from generated code. > > Thanks to Andrew Baumann for his reminder that this patch was > still missing. Andrew, could you please test it with your > RPi emulation? > > Regards, > Stefan > > cpu-exec.c | 9 +++++++++ > include/sysemu/os-win32.h | 8 -------- > 2 files changed, 9 insertions(+), 8 deletions(-) > > diff --git a/cpu-exec.c b/cpu-exec.c > index fd92452..6a725e0 100644 > --- a/cpu-exec.c > +++ b/cpu-exec.c > @@ -33,6 +33,15 @@ > #endif > #include "sysemu/replay.h" > > +#if defined(_WIN64) > +/* On w64, sigsetjmp is implemented by _setjmp which needs a second > parameter. > + * If this parameter is NULL, longjump does no stack unwinding. > + * That is what we need for QEMU. Passing the value of register rsp > (default) > + * lets longjmp try a stack unwinding which will crash with generated code. > */ > +#undef sigsetjmp > +#define sigsetjmp(env, savesigs) _setjmp(env, NULL) > +#endif > + > /* -icount align implementation. */ > > typedef struct SyncClocks { > diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h > index fbed346..b151e74 100644 > --- a/include/sysemu/os-win32.h > +++ b/include/sysemu/os-win32.h > @@ -55,14 +55,6 @@ > # define EWOULDBLOCK WSAEWOULDBLOCK > #endif > > -#if defined(_WIN64) > -/* On w64, setjmp is implemented by _setjmp which needs a second > parameter. > - * If this parameter is NULL, longjump does no stack unwinding. > - * That is what we need for QEMU. Passing the value of register rsp (default) > - * lets longjmp try a stack unwinding which will crash with generated code. > */ > -# undef setjmp > -# define setjmp(env) _setjmp(env, NULL) > -#endif > /* QEMU uses sigsetjmp()/siglongjmp() as the portable way to specify > * "longjmp and don't touch the signal masks". Since we know that the > * savemask parameter will always be zero we can safely define these > -- > 2.1.4 Thanks Stefan. This works for me with a mingw64 native build. Tested-by: Andrew Baumann <Andrew.Baumann@microsoft.com> Andrew
On 1 March 2016 at 05:07, Stefan Weil <sw@weilnetz.de> wrote: > The rest of the code can use longjmp with stack unwinding. > > Signed-off-by: Stefan Weil <sw@weilnetz.de> > --- > > This is a bug fix needed for 64 bit Windows. > > QEMU for Windows currently gets the wrong definition for > sigsetjmp. It uses stack unwinding for longjmp which results > in a crash when it is called from generated code. > > Thanks to Andrew Baumann for his reminder that this patch was > still missing. Andrew, could you please test it with your > RPi emulation? I don't understand this patch. Why doesn't it work to have sigsetjmp() be implemented the same way for every use that QEMU makes of it? thanks -- PMM
Am 01.03.2016 um 10:59 schrieb Peter Maydell: > On 1 March 2016 at 05:07, Stefan Weil <sw@weilnetz.de> wrote: >> The rest of the code can use longjmp with stack unwinding. >> >> Signed-off-by: Stefan Weil <sw@weilnetz.de> >> --- >> >> This is a bug fix needed for 64 bit Windows. >> >> QEMU for Windows currently gets the wrong definition for >> sigsetjmp. It uses stack unwinding for longjmp which results >> in a crash when it is called from generated code. >> >> Thanks to Andrew Baumann for his reminder that this patch was >> still missing. Andrew, could you please test it with your >> RPi emulation? > I don't understand this patch. Why doesn't it work to have > sigsetjmp() be implemented the same way for every use that > QEMU makes of it? > > thanks > -- PMM It does, as long as the "same way" is the correct one, namely the one without stack unwinding. The current code used to work, but re-arranged include files broke the working code somewhere in the past: include/sysemu/os-win32.h does the right thing at the wrong place. Its correct definition of sigsetjmp is overwritten by the definition from a Mingw-w64 system header file which triggers stack unwinding. Stack unwinding is fatal for QEMU's generated code. My patch makes sure that the critical code in cpu-exec.c gets the correct definition of sigsetjmp. In addition, it removes code which might or might not change the default definition of sigsetjmp (depending on the order of include files). Now all other files beside cpu-exec.c will use the default behaviour with stack unwinding. Regards, Stefan
On 1 March 2016 at 11:54, Stefan Weil <sw@weilnetz.de> wrote: > Am 01.03.2016 um 10:59 schrieb Peter Maydell: >> I don't understand this patch. Why doesn't it work to have >> sigsetjmp() be implemented the same way for every use that >> QEMU makes of it? > It does, as long as the "same way" is the correct one, namely > the one without stack unwinding. > > The current code used to work, but re-arranged include files > broke the working code somewhere in the past: > > include/sysemu/os-win32.h does the right thing at the > wrong place. Its correct definition of sigsetjmp is overwritten by > the definition from a Mingw-w64 system header file which > triggers stack unwinding. Stack unwinding is fatal for > QEMU's generated code. > > My patch makes sure that the critical code in cpu-exec.c > gets the correct definition of sigsetjmp. I think we should fix this by making sure that osdep.h does the right thing -- ie that it gives us the correct definition and prevents mingw's headers from overriding it with the wrong thing (by ensuring that the offending system header is included before we redefine things, or however necessary). This is what osdep.h's purpose is -- to hide annoying system-header workarounds and hacks rather than putting them in the rest of QEMU code. > In addition, it removes code which might or might not > change the default definition of sigsetjmp (depending > on the order of include files). Now all other files beside > cpu-exec.c will use the default behaviour with stack > unwinding. That seems wrong -- we should have the same behaviour for sigsetjmp/siglongjmp everywhere we use it. thanks -- PMM
Am 01.03.2016 um 13:22 schrieb Peter Maydell: > On 1 March 2016 at 11:54, Stefan Weil <sw@weilnetz.de> wrote: >> Am 01.03.2016 um 10:59 schrieb Peter Maydell: >>> I don't understand this patch. Why doesn't it work to have >>> sigsetjmp() be implemented the same way for every use that >>> QEMU makes of it? >> It does, as long as the "same way" is the correct one, namely >> the one without stack unwinding. >> >> The current code used to work, but re-arranged include files >> broke the working code somewhere in the past: >> >> include/sysemu/os-win32.h does the right thing at the >> wrong place. Its correct definition of sigsetjmp is overwritten by >> the definition from a Mingw-w64 system header file which >> triggers stack unwinding. Stack unwinding is fatal for >> QEMU's generated code. >> >> My patch makes sure that the critical code in cpu-exec.c >> gets the correct definition of sigsetjmp. > I think we should fix this by making sure that osdep.h > does the right thing -- ie that it gives us the correct > definition and prevents mingw's headers from overriding it > with the wrong thing (by ensuring that the offending system > header is included before we redefine things, or however > necessary). This is what osdep.h's purpose is -- to hide > annoying system-header workarounds and hacks rather than > putting them in the rest of QEMU code. > >> In addition, it removes code which might or might not >> change the default definition of sigsetjmp (depending >> on the order of include files). Now all other files beside >> cpu-exec.c will use the default behaviour with stack >> unwinding. > That seems wrong -- we should have the same behaviour for > sigsetjmp/siglongjmp everywhere we use it. > > thanks > -- PMM Technically there is nothing wrong with using different behaviour for each setjmp or sigsetjmp. The "best" solution would be to add any prologue / epilogue which is needed for stack unwinding to the generated code. Like that, no tricks with redefinitions of setjmp / sigsetjmp would be necessary. As long as that solution is not available, I'd prefer the variant which is implemented by my patch and keep the workaround close to the single location where it is needed. Your alternate solution would require inclusion of setjmp.h in include/sysemu/os-win32.h. Then every compilation for Windows would get that header file, resulting in a (small) overhead. In addition, there would be no stack unwinding for any setjmp/longjmp which is not the standard behaviour for Windows 64 bit (but which we had until it was broken). I simply don't know whether this has unwanted side effects (maybe for debugging or with crash dumps) - that's the reason why I'd minimize the non-standard behaviour. Regards, Stefan
diff --git a/cpu-exec.c b/cpu-exec.c index fd92452..6a725e0 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -33,6 +33,15 @@ #endif #include "sysemu/replay.h" +#if defined(_WIN64) +/* On w64, sigsetjmp is implemented by _setjmp which needs a second parameter. + * If this parameter is NULL, longjump does no stack unwinding. + * That is what we need for QEMU. Passing the value of register rsp (default) + * lets longjmp try a stack unwinding which will crash with generated code. */ +#undef sigsetjmp +#define sigsetjmp(env, savesigs) _setjmp(env, NULL) +#endif + /* -icount align implementation. */ typedef struct SyncClocks { diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h index fbed346..b151e74 100644 --- a/include/sysemu/os-win32.h +++ b/include/sysemu/os-win32.h @@ -55,14 +55,6 @@ # define EWOULDBLOCK WSAEWOULDBLOCK #endif -#if defined(_WIN64) -/* On w64, setjmp is implemented by _setjmp which needs a second parameter. - * If this parameter is NULL, longjump does no stack unwinding. - * That is what we need for QEMU. Passing the value of register rsp (default) - * lets longjmp try a stack unwinding which will crash with generated code. */ -# undef setjmp -# define setjmp(env) _setjmp(env, NULL) -#endif /* QEMU uses sigsetjmp()/siglongjmp() as the portable way to specify * "longjmp and don't touch the signal masks". Since we know that the * savemask parameter will always be zero we can safely define these
The rest of the code can use longjmp with stack unwinding. Signed-off-by: Stefan Weil <sw@weilnetz.de> --- This is a bug fix needed for 64 bit Windows. QEMU for Windows currently gets the wrong definition for sigsetjmp. It uses stack unwinding for longjmp which results in a crash when it is called from generated code. Thanks to Andrew Baumann for his reminder that this patch was still missing. Andrew, could you please test it with your RPi emulation? Regards, Stefan cpu-exec.c | 9 +++++++++ include/sysemu/os-win32.h | 8 -------- 2 files changed, 9 insertions(+), 8 deletions(-)