On Sat, Jan 25, 2025 at 06:59:32PM +0000, Maciej W. Rozycki wrote: > On Sat, 25 Jan 2025, Maciej W. Rozycki wrote: > > > > Interesting. Perhaps these frames are aligned by PAL-code as well, > > > the reference manual wasn't clear about that. > > > > I think it just boils down to the amount of exception nesting. > > Ah, actually most of these faults were entered from the user mode and the > kernel stack starts at a page boundary, so once the stack frame has been > allocated by PALcode and SAVE_ALL combined the stack pointer ends up > misaligned. For faults entered from the kernel mode the opposite might be > the case. Indeed, sounds plausible. > So unless we want to play (and we don't) with FP and the saving > and restoration of SP, we just want to keep SP aligned at all times. > > > I knew about entUna, I thought it's safe as it only deals with 64-bit data > > > and not going to be changed in future, but missed entMM... > > > > > > I agree, better fix both. > > > > Well, we may get away with it in many cases, which is obviously why > > this bug has survived so long, but in principle it is not safe to enter > > C code with the stack misaligned, so yes, we need to fix all the code > > paths, also because a nested exception will cause hell to break loose. > > > > Here just bumping up the frame size and adjusting offsets in assembly > > code accordingly so as to account for the empty longword at the bottom > > of the frame should do, just as I did across my change. > > ... or, depending on how you look at it, top of the frame and FAOD in any > case the longword closest to the stack pointer will be the empty one. Right. So if we agree on my variant, this addition patch is needed. [No problems with gdb, as expected.] Ivan. diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S index 6fb38365539d..f4d41b4538c2 100644 --- a/arch/alpha/kernel/entry.S +++ b/arch/alpha/kernel/entry.S @@ -194,8 +194,8 @@ CFI_END_OSF_FRAME entArith CFI_START_OSF_FRAME entMM SAVE_ALL /* save $9 - $15 so the inline exception code can manipulate them. */ - subq $sp, 56, $sp - .cfi_adjust_cfa_offset 56 + subq $sp, 64, $sp + .cfi_adjust_cfa_offset 64 stq $9, 0($sp) stq $10, 8($sp) stq $11, 16($sp) @@ -210,7 +210,7 @@ CFI_START_OSF_FRAME entMM .cfi_rel_offset $13, 32 .cfi_rel_offset $14, 40 .cfi_rel_offset $15, 48 - addq $sp, 56, $19 + addq $sp, 64, $19 /* handle the fault */ lda $8, 0x3fff bic $sp, $8, $8 @@ -223,7 +223,7 @@ CFI_START_OSF_FRAME entMM ldq $13, 32($sp) ldq $14, 40($sp) ldq $15, 48($sp) - addq $sp, 56, $sp + addq $sp, 64, $sp .cfi_restore $9 .cfi_restore $10 .cfi_restore $11 @@ -231,7 +231,7 @@ CFI_START_OSF_FRAME entMM .cfi_restore $13 .cfi_restore $14 .cfi_restore $15 - .cfi_adjust_cfa_offset -56 + .cfi_adjust_cfa_offset -64 /* finish up the syscall as normal. */ br ret_from_sys_call CFI_END_OSF_FRAME entMM @@ -378,8 +378,8 @@ entUnaUser: .cfi_restore $0 .cfi_adjust_cfa_offset -256 SAVE_ALL /* setup normal kernel stack */ - lda $sp, -56($sp) - .cfi_adjust_cfa_offset 56 + lda $sp, -64($sp) + .cfi_adjust_cfa_offset 64 stq $9, 0($sp) stq $10, 8($sp) stq $11, 16($sp) @@ -395,7 +395,7 @@ entUnaUser: .cfi_rel_offset $14, 40 .cfi_rel_offset $15, 48 lda $8, 0x3fff - addq $sp, 56, $19 + addq $sp, 64, $19 bic $sp, $8, $8 jsr $26, do_entUnaUser ldq $9, 0($sp) @@ -405,7 +405,7 @@ entUnaUser: ldq $13, 32($sp) ldq $14, 40($sp) ldq $15, 48($sp) - lda $sp, 56($sp) + lda $sp, 64($sp) .cfi_restore $9 .cfi_restore $10 .cfi_restore $11 @@ -413,7 +413,7 @@ entUnaUser: .cfi_restore $13 .cfi_restore $14 .cfi_restore $15 - .cfi_adjust_cfa_offset -56 + .cfi_adjust_cfa_offset -64 br ret_from_sys_call CFI_END_OSF_FRAME entUna
