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quemu-user 32-bit fixes in support of building Proton in linux/amd64 containers on non-Intel hosts #350

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quemu-user 32-bit fixes in support of building Proton in linux/amd64 containers on non-Intel hosts #350

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c4c715e
ntdll: Keep reserved area bounds page aligned when avoiding 4GB wrap-…
natbro Aug 22, 2026
c810945
ntdll: Infer the trap number in segv_handler() when the context lacks…
natbro Aug 22, 2026
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13 changes: 12 additions & 1 deletion dlls/ntdll/unix/signal_i386.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1977,8 +1977,19 @@ static void segv_handler( int signal, siginfo_t *siginfo, void *sigcontext )
ucontext_t *ucontext = sigcontext;
void *stack = setup_exception_record( sigcontext, &rec, &xcontext );
void *steamclient_addr = NULL;
int trap = TRAP_sig(ucontext);

switch (TRAP_sig(ucontext))
/* qemu-user synthesizes signal frames without filling in the trap number,
* leaving it -1, so the dispatch below falls through to the default case and
* the fault is never serviced. Infer it from the signal instead. */
if (trap < 0) switch (signal)
{
case SIGSEGV: trap = TRAP_x86_PAGEFLT; break;
case SIGBUS: trap = TRAP_x86_ALIGNFLT; break;
case SIGILL: trap = TRAP_x86_PRIVINFLT; break;
}

switch (trap)
{
case TRAP_x86_OFLOW: /* Overflow exception */
rec.ExceptionCode = EXCEPTION_INT_OVERFLOW;
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14 changes: 12 additions & 2 deletions dlls/ntdll/unix/virtual.c
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Original file line number Diff line number Diff line change
Expand Up @@ -574,7 +574,12 @@ static void mmap_add_reserved_area( void *addr, SIZE_T size )
assert( !((UINT_PTR)addr & host_page_mask) );
assert( !(size & host_page_mask) );

if (!((intptr_t)addr + size)) size--; /* avoid wrap-around */
/* An area ending exactly at the 4GB boundary wraps addr+size to 0. Back it off
* by a whole page rather than a single byte, so that the area bounds stay page
* aligned as the asserts above require; consumers such as alloc_virtual_heap()
* derive addresses from the area end and would otherwise be handed an
* unaligned one. */
if (size >= host_page_size && !((intptr_t)addr + size)) size -= host_page_size;
end = (char *)addr + size;

LIST_FOR_EACH( ptr, &reserved_areas )
Expand Down Expand Up @@ -626,7 +631,12 @@ static void mmap_remove_reserved_area( void *addr, SIZE_T size )
assert( !((UINT_PTR)addr & host_page_mask) );
assert( !(size & host_page_mask) );

if (!((intptr_t)addr + size)) size--; /* avoid wrap-around */
/* An area ending exactly at the 4GB boundary wraps addr+size to 0. Back it off
* by a whole page rather than a single byte, so that the area bounds stay page
* aligned as the asserts above require; consumers such as alloc_virtual_heap()
* derive addresses from the area end and would otherwise be handed an
* unaligned one. */
if (size >= host_page_size && !((intptr_t)addr + size)) size -= host_page_size;

ptr = list_head( &reserved_areas );
/* find the first area covering address */
Expand Down