Re: [Sbcl-devel] [Sbcl-commits] master: arm64-arch.c: Fix soft-simulation of some instructions.

[Stas B. <sta...@gm...>]

On Thu, May 21, 2026 at 11:09 AM Charles Zhang <cha...@ya...> wrote:
>
> Oh, right. Thanks for tracking these issues down.

I just fed the function to an llm.

> I look forward to any masochist’s x86-64 software implementation to make breakpoint tracing thread safe. :)
>
> On Thursday, May 21, 2026, 12:30 AM, Stas Boukarev <sta...@gm...> wrote:
>
> It's a safepoint.
>
> On Thu, May 21, 2026 at 12:22 AM Charles Zhang <cha...@ya...> wrote:
> >
> > Thanks. Not a proper fix because I don't have a Windows machine. I'm thoroughly confused about why this is Windows only.
> >
> >
> >
> >
> >
> > On Wednesday, May 20, 2026 at 08:29:14 PM GMT+2, Stas Boukarev <sta...@gm...> wrote:
> >
> >
> > ::: Running (TRACE :ENCAPSULATE NIL)
> > fatal error encountered in SBCL pid 5521255184:
> > Unsupported LDR (literal) variant.
> > 0: 00000291caaa1938 pc=0000001000181ed0 {0000001000181dc0+0110}
> > SB-DI::BREAKPOINT-DO-DISPLACED-INST
> > 1: 00000291caaa1928 pc=00007ff7531059e0
> > 2: 00000291caaa1900 pc=00000010019d75e0 {00000010019d7580+0060}
> > CL-USER::TRACE-THIS
> >
> > On Wed, May 20, 2026 at 1:14 PM apache--- via Sbcl-commits
> > <sbc...@li...> wrote:
> > >
> > > The branch "master" has been updated in SBCL:
> > >        via  f982475b0bcb6d691cf172630fad9c14087378b2 (commit)
> > >      from  07f82d35917900fe1222891579c2fe9d3d8df3c4 (commit)
> > >
> > > - Log -----------------------------------------------------------------
> > > commit f982475b0bcb6d691cf172630fad9c14087378b2
> > > Author: Charles Zhang <cha...@ya...>
> > > Date:  Tue Mar 17 15:18:20 2026 +0100
> > >
> > >    arm64-arch.c: Fix soft-simulation of some instructions.
> > >
> > >    For breakpoint support.
> > > ---
> > >  src/runtime/arm64-arch.c | 63 ++++++++++++++++++++++++++++++------------------
> > >  1 file changed, 39 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/src/runtime/arm64-arch.c b/src/runtime/arm64-arch.c
> > > index 9183013fe..e9e8d3af1 100644
> > > --- a/src/runtime/arm64-arch.c
> > > +++ b/src/runtime/arm64-arch.c
> > > @@ -88,20 +88,35 @@ condition_holds(os_context_t *context, unsigned int cond)
> > >  {
> > >      int flags = *os_context_flags_addr(context);
> > >      bool result;
> > > -    // Evaluate base condition.
> > > -    switch (cond) {
> > > -    case 0b000: result = ((flags >> Z_BIT) & 1);
> > > -    case 0b001: result = ((flags >> C_BIT) & 1);
> > > -    case 0b010: result = ((flags >> N_BIT) & 1);
> > > -    case 0b011: result = ((flags >> V_BIT) & 1);
> > > -    case 0b100: result = ((flags >> V_BIT) & 1) && ~((flags >> Z_BIT) & 1);
> > > -    case 0b101: result = ((flags >> N_BIT) == (flags >> V_BIT));
> > > -    case 0b110: result = ((flags >> N_BIT) == (flags >> V_BIT)) && !((flags >> Z_BIT) & 1);
> > > -    case 0b111: result = 1;
> > > +    // Evaluate base condition (ignoring the inversion bit).
> > > +    switch (cond >> 1) {
> > > +    case 0b000:
> > > +      result = (flags >> Z_BIT) & 1;
> > > +      break;
> > > +    case 0b001:
> > > +      result = (flags >> C_BIT) & 1;
> > > +      break;
> > > +    case 0b010:
> > > +      result = (flags >> N_BIT) & 1;
> > > +      break;
> > > +    case 0b011: result = (flags >> V_BIT) & 1;
> > > +      break;
> > > +    case 0b100:
> > > +      result = ((flags >> C_BIT) & 1) && !((flags >> Z_BIT) & 1);
> > > +      break;
> > > +    case 0b101:
> > > +      result = ((flags >> N_BIT) & 1) == ((flags >> V_BIT) & 1);
> > > +      break;
> > > +    case 0b110:
> > > +      result = ((flags >> N_BIT) & 1) == ((flags >> V_BIT) & 1) && !((flags >> Z_BIT) & 1);
> > > +      break;
> > > +    default:
> > > +      result = 1;
> > > +      break;
> > >      }
> > >
> > > -    // Condition flag values in the set '111x' indicate always true
> > > -    // Otherwise, invert condition if necessary.
> > > +    // Condition flag values in the set '111x' indicate always true.
> > > +    // Otherwise, invert condition if the low bit is set.
> > >      if ((cond & 0b1) && (cond != 0b1111))
> > >          result = !result;
> > >
> > > @@ -158,12 +173,10 @@ void arch_do_displaced_inst(os_context_t *context, unsigned int orig_inst)
> > >      }
> > >      else if (((orig_inst >> 25) & 0b111111) == 0b011010) {
> > >          // Compare branch imm
> > > -        bool size_is_64 = (orig_inst >> 31) & 0b1;
> > >          bool op = (orig_inst >> 24) & 0b1;
> > >          int offset = sign_extend((orig_inst >> 5) & ~(1 << 19), 19);
> > >          int rt = orig_inst & 0b11111;
> > > -        if (!size_is_64) lose("Size must be 64 bits.");
> > > -        if (*os_context_register_addr(context, rt) ^ op)
> > > +        if ((!*os_context_register_addr(context, rt)) ^ op)
> > >              next_pc += offset;
> > >          else
> > >              next_pc += 1;
> > > @@ -173,32 +186,34 @@ void arch_do_displaced_inst(os_context_t *context, unsigned int orig_inst)
> > >          bool b5 = (orig_inst >> 31) & 0b1;
> > >          bool op = (orig_inst >> 24) & 0b1;
> > >          bool b40 = (orig_inst >> 19) & 0b11111;
> > > -        int bit_pos = (b5 << 6) | b40;
> > > +        int bit_pos = (b5 << 5) | b40;
> > >          int offset = sign_extend((orig_inst >> 5) & ~(1 << 14), 14);
> > >          int rt = orig_inst & 0b11111;
> > > -        if (!b5) lose("b5 must be 64 bits.");
> > >          if (((*os_context_register_addr(context, rt) >> bit_pos) & 0b1) ^ op)
> > >              next_pc += offset;
> > >          else
> > >              next_pc += 1;
> > >      }
> > > -    else if (((orig_inst >> 31) & 0b1) == 0b0) {
> > > +    else if (((orig_inst >> 24) & 0b11111) == 0b11000) {
> > >          // LDR (literal)
> > > -        bool size_is_64 = (orig_inst >> 30) & 0b1;
> > > +        int opc = (orig_inst >> 30) & 0b11;
> > >          int rt = orig_inst & 0b11111;
> > >          int offset = sign_extend((orig_inst >> 5) & ~(1 << 19), 19);
> > > -        if (!size_is_64) lose("Size must be 64 bits.");
> > > -        *os_context_register_addr(context, rt) = *((lispobj*)(pc + offset));
> > > +        if (opc == 0b01)
> > > +          *os_context_register_addr(context, rt) = *((uint64_t *)(pc + offset));
> > > +        else if (opc == 0b00)
> > > +          *os_context_register_addr(context, rt) = *((uint32_t *)(pc + offset));
> > > +        else
> > > +          lose("Unsupported LDR (literal) variant.");
> > >          next_pc += 1;
> > >      }
> > >      else if (((orig_inst >> 24) & 0b11111) == 0b10000) {
> > >          // ADR(P)
> > >          bool op = (orig_inst >> 31) & 0b1;
> > >          int rd = orig_inst & 0b11111;
> > > -        int imm = sign_extend(((orig_inst >> 5) & ~(1 << 19)) |
> > > -                              ((orig_inst >> 29) & ~(1 << 2)), 21);
> > > +        int imm = sign_extend(((orig_inst >> 3) & 0x1FFFFC) | ((orig_inst >> 29) & 3), 21);
> > >          if (op) // ADRP
> > > -            *os_context_register_addr(context, rd) = ((uword_t)pc & ~(1 << 12)) + (imm << 12);
> > > +            *os_context_register_addr(context, rd) = ((uword_t)pc & ~(uword_t)0xFFF) + ((sword_t)imm << 12);
> > >          else // ADR
> > >              *os_context_register_addr(context, rd) = (uword_t)pc + imm;
> > >          next_pc += 1;
> > >
> > > -----------------------------------------------------------------------
> > >
> > >
> > > hooks/post-receive
> > > --
> > > SBCL
> > >
> > >
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