On Sun, Sep 12, 2021 at 10:49:25AM -0700, Richard Henderson wrote: > With arm32, the ABI gives us 8-byte alignment for the stack. > While it's possible to realign the stack to provide 16-byte alignment, > it's far easier to simply not encode 16-byte alignment in the > VLD1 and VST1 instructions that we emit. > > Remove the assertion in temp_allocate_frame, limit natural alignment > to the provided stack alignment, and add a comment. > > Reported-by: Richard W.M. Jones <rjo...@redhat.com> > Signed-off-by: Richard Henderson <richard.hender...@linaro.org> > --- > > I haven't seen the assertion with the various arm kernels that I happen > to have laying about. I have not taken the time to build the combo > from the bug report: > > [ 0.000000] Linux version 5.14.0-60.fc36.armv7hl > (mockbu...@buildvm-a32-12.iad2.fedoraproject.org) (gcc (GCC) 11.2.1 20210728 > (Red Hat 11.2.1-1), GNU ld version 2.37-9.fc36) #1 SMP Mon Aug 30 14:08:34 > UTC 2021 > > I thought about parameterizing this patch further, but I can't think of > another ISA that would be affected. (i686 clumsily changed its abi 20 > years ago to avoid faulting on vector spills; other isas so far have > allowed vectors to be unaligned.)
Is it possible this change could have caused a more serious regression? Now when I try to boot the Fedora kernel using TCG on armv7hl I can't even get to the point where it detects virtio-scsi devices. Full log is here (go down to the bottom and work backwards): https://kojipkgs.fedoraproject.org//work/tasks/7337/75597337/build.log This might have been caused by a coincidental change to the kernel. The test environment I have makes it extremely difficult to test this change in isolation. However I do know that the same error does _not_ occur on x86-64 guest/host with this patch applied. Rich. > > r~ > --- > tcg/tcg.c | 8 +++++++- > tcg/arm/tcg-target.c.inc | 13 +++++++++---- > 2 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/tcg/tcg.c b/tcg/tcg.c > index 4142d42d77..ca5bcc4635 100644 > --- a/tcg/tcg.c > +++ b/tcg/tcg.c > @@ -3060,7 +3060,13 @@ static void temp_allocate_frame(TCGContext *s, TCGTemp > *ts) > g_assert_not_reached(); > } > > - assert(align <= TCG_TARGET_STACK_ALIGN); > + /* > + * Assume the stack is sufficiently aligned. > + * This affects e.g. ARM NEON, where we have 8 byte stack alignment > + * and do not require 16 byte vector alignment. This seems slightly > + * easier than fully parameterizing the above switch statement. > + */ > + align = MIN(TCG_TARGET_STACK_ALIGN, align); > off = ROUND_UP(s->current_frame_offset, align); > > /* If we've exhausted the stack frame, restart with a smaller TB. */ > diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc > index e5b4f86841..8515717435 100644 > --- a/tcg/arm/tcg-target.c.inc > +++ b/tcg/arm/tcg-target.c.inc > @@ -2477,8 +2477,13 @@ static void tcg_out_ld(TCGContext *s, TCGType type, > TCGReg arg, > tcg_out_vldst(s, INSN_VLD1 | 0x7d0, arg, arg1, arg2); > return; > case TCG_TYPE_V128: > - /* regs 2; size 8; align 16 */ > - tcg_out_vldst(s, INSN_VLD1 | 0xae0, arg, arg1, arg2); > + /* > + * We have only 8-byte alignment for the stack per the ABI. > + * Rather than dynamically re-align the stack, it's easier > + * to simply not request alignment beyond that. So: > + * regs 2; size 8; align 8 > + */ > + tcg_out_vldst(s, INSN_VLD1 | 0xad0, arg, arg1, arg2); > return; > default: > g_assert_not_reached(); > @@ -2497,8 +2502,8 @@ static void tcg_out_st(TCGContext *s, TCGType type, > TCGReg arg, > tcg_out_vldst(s, INSN_VST1 | 0x7d0, arg, arg1, arg2); > return; > case TCG_TYPE_V128: > - /* regs 2; size 8; align 16 */ > - tcg_out_vldst(s, INSN_VST1 | 0xae0, arg, arg1, arg2); > + /* See tcg_out_ld re alignment: regs 2; size 8; align 8 */ > + tcg_out_vldst(s, INSN_VST1 | 0xad0, arg, arg1, arg2); > return; > default: > g_assert_not_reached(); > -- > 2.25.1 -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW