On Wed, Jul 04, 2007 at 11:31:30PM +0100, Pedro Alves wrote:
> Kevin O'Connor wrote:
> > I think future versions of gcc wont guarantee function placement
> > relative to top-level asm statements.
> >
>
> Ah, you're paying attention. :) It will certainly fail today if
> we use -ffunction-sections. If this ever turns into a real problem,
> and we don't have real __try/__except support in the compiler, we
> can craft an __attribute__((seh ("handler")) into gcc. I think that
> is much easier.
I get things reordered today when using -O. Also, I saw on the gcc
website (can't find link now) that they plan on being more aggressive
with this in the future.
> > I'll try to take some of the sample code and integrate it into haret.
> >
>
> Great, please do post here your findings. I'd be curious if you take the
> simplest route of not tweaking the current thread's context and just longjmp
> from the seh handler, and if it brings any real problems (I don't think it's
> safe, but it would be great to be proved wrong).
Attached is what I've done. Oddly, longjmp directly from the handler
seems to work, but returning via EXCEPTION_CONTINUE_EXECUTION fails.
Not sure what I'm doing wrong.
I use my new handlers with:
struct eh_data ehd;
if (start_ehandling(&ehd)) {
while (wcount--)
*vaddr++ = value;
end_ehandling(&ehd);
} else {
Output(C_ERROR "EXCEPTION while writing %08x to address %p",
value, vaddr);
}
Finally, I call init_ehandling at startup.
-Kevin
#include <setjmp.h> // jmp_buf
struct eh_data {
jmp_buf env;
};
int start_ehandling(struct eh_data *d);
void end_ehandling(struct eh_data *d);
void init_thread_ehandling(void);
void init_ehandling(void);
#include <windows.h> // TlsSetValue
#include "output.h" // Output
#include "exceptions.h"
static DWORD handler_tls;
int start_ehandling(struct eh_data *d)
{
TlsSetValue(handler_tls, d);
return !setjmp(d->env);
}
void end_ehandling(struct eh_data *d)
{
TlsSetValue(handler_tls, NULL);
}
void init_thread_ehandling(void)
{
TlsSetValue(handler_tls, NULL);
}
void init_ehandling(void)
{
handler_tls = TlsAlloc();
}
extern "C" long
eh_handler(struct _EXCEPTION_RECORD *ExceptionRecord,
void *EstablisherFrame,
struct _CONTEXT *ContextRecord,
struct _DISPATCHER_CONTEXT *DispatcherContext)
{
Output("In handler");
struct eh_data *d = (struct eh_data*)TlsGetValue(handler_tls);
if (! d) {
Output(C_ERROR "Terminating haret due to unhandled exception");
exit(1);
}
end_ehandling(d);
// XXX
longjmp(d->env, 1);
ContextRecord->Pc = (ulong)longjmp;
ContextRecord->R0 = (ulong)d->env;
ContextRecord->R1 = 1;
Output("Leaving handler");
return EXCEPTION_CONTINUE_EXECUTION;
}
__asm__(
// Data to be placed at start of .text section
"\t.section .init\n"
"\t.word eh_handler\n"
"\t.word 0\n"
"start_eh_text:\n"
// Data for exception handler
"\t.section .pdata\n"
"\t.word start_eh_text\n"
"\t.word 0xc0000002 | (0xFFFFF << 8)\n" // max 22 bits for number of
instructions
"\t.text\n"
);
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