Re: [PATCH v6a 08/15] gdb: Update x86 Linux architectures to support XSAVE layouts.

[John Baldwin <jhb@FreeBSD.org>]

On 7/28/23 2:29 PM, John Baldwin wrote:
> Refactor i386_linux_core_read_xcr0 to fetch and return a corresponding
> x86_xsave_layout as well as xcr0 using the size of an existing
> NT_X86_XSTATE core dump to determine the offsets via
> i387_guess_xsave_layout.  Use this to add an implementation of
> gdbarch_core_xfer_x86_xsave_layout.
> 
> Use tdep->xsave_layout.sizeof_xsave as the size of the XSTATE register
> set.
> ---
>    gdb/amd64-linux-tdep.c | 13 +++++++--
>    gdb/i386-linux-tdep.c  | 66 +++++++++++++++++++++++-------------------
>    gdb/i386-linux-tdep.h  | 25 +++++++++-------
>    3 files changed, 61 insertions(+), 43 deletions(-)
> 
> diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
> index cbbac1a0c64..e2fdf5fb6c8 100644
> --- a/gdb/amd64-linux-tdep.c
> +++ b/gdb/amd64-linux-tdep.c
> @@ -1616,7 +1616,10 @@ amd64_linux_core_read_description (struct gdbarch *gdbarch,
>    				  bfd *abfd)
>    {
>      /* Linux/x86-64.  */
> -  uint64_t xcr0 = i386_linux_core_read_xcr0 (abfd);
> +  x86_xsave_layout layout;
> +  uint64_t xcr0 = i386_linux_core_read_xsave_info (abfd, layout);
> +  if (xcr0 == 0)
> +    xcr0 = X86_XSTATE_SSE_MASK;
>    
>      return amd64_linux_read_description (xcr0 & X86_XSTATE_ALL_MASK,
>    				       gdbarch_ptr_bit (gdbarch) == 32);
> @@ -1661,8 +1664,10 @@ amd64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>    
>      cb (".reg", 27 * 8, 27 * 8, &i386_gregset, NULL, cb_data);
>      cb (".reg2", 512, 512, &amd64_fpregset, NULL, cb_data);
> -  cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0), X86_XSTATE_SIZE (tdep->xcr0),
> -      &amd64_linux_xstateregset, "XSAVE extended state", cb_data);
> +  if (tdep->xsave_layout.sizeof_xsave != 0)
> +    cb (".reg-xstate", tdep->xsave_layout.sizeof_xsave,
> +	tdep->xsave_layout.sizeof_xsave, &amd64_linux_xstateregset,
> +	"XSAVE extended state", cb_data);
>    }
>    
>    /* The instruction sequences used in x86_64 machines for a
> @@ -1804,6 +1809,8 @@ amd64_linux_init_abi_common(struct gdbarch_info info, struct gdbarch *gdbarch,
>      tdep->sc_num_regs = ARRAY_SIZE (amd64_linux_sc_reg_offset);
>    
>      tdep->xsave_xcr0_offset = I386_LINUX_XSAVE_XCR0_OFFSET;
> +  set_gdbarch_core_read_x86_xsave_layout
> +    (gdbarch, i386_linux_core_read_x86_xsave_layout);
>    
>      /* Add the %orig_rax register used for syscall restarting.  */
>      set_gdbarch_write_pc (gdbarch, amd64_linux_write_pc);
> diff --git a/gdb/i386-linux-tdep.c b/gdb/i386-linux-tdep.c
> index 554c1455a5f..7ff7c155e2c 100644
> --- a/gdb/i386-linux-tdep.c
> +++ b/gdb/i386-linux-tdep.c
> @@ -638,45 +638,48 @@ static int i386_linux_sc_reg_offset[] =
>      0 * 4				/* %gs */
>    };
>    
> -/* Get XSAVE extended state xcr0 from core dump.  */
> +/* See i386-linux-tdep.h.  */
>    
>    uint64_t
> -i386_linux_core_read_xcr0 (bfd *abfd)
> +i386_linux_core_read_xsave_info (bfd *abfd, x86_xsave_layout &layout)
>    {
>      asection *xstate = bfd_get_section_by_name (abfd, ".reg-xstate");
> -  uint64_t xcr0;
> +  if (xstate == nullptr)
> +    return 0;
>    
> -  if (xstate)
> +  /* Check extended state size.  */
> +  size_t size = bfd_section_size (xstate);
> +  if (size < X86_XSTATE_AVX_SIZE)
> +    return 0;
> +
> +  char contents[8];
> +  if (! bfd_get_section_contents (abfd, xstate, contents,
> +				  I386_LINUX_XSAVE_XCR0_OFFSET, 8))
>        {
> -      size_t size = bfd_section_size (xstate);
> -
> -      /* Check extended state size.  */
> -      if (size < X86_XSTATE_AVX_SIZE)
> -	xcr0 = X86_XSTATE_SSE_MASK;
> -      else
> -	{
> -	  char contents[8];
> -
> -	  if (! bfd_get_section_contents (abfd, xstate, contents,
> -					  I386_LINUX_XSAVE_XCR0_OFFSET,
> -					  8))
> -	    {
> -	      warning (_("Couldn't read `xcr0' bytes from "
> -			 "`.reg-xstate' section in core file."));
> -	      return 0;
> -	    }
> -
> -	  xcr0 = bfd_get_64 (abfd, contents);
> -	}
> +      warning (_("Couldn't read `xcr0' bytes from "
> +		 "`.reg-xstate' section in core file."));
> +      return 0;
>        }
> -  else
> -    xcr0 = 0;
> +
> +  uint64_t xcr0 = bfd_get_64 (abfd, contents);
> +
> +  if (!i387_guess_xsave_layout (xcr0, size, layout))
> +    return 0;
>    
>      return xcr0;
>    }
>    
>    /* See i386-linux-tdep.h.  */
>    
> +bool
> +i386_linux_core_read_x86_xsave_layout (struct gdbarch *gdbarch,
> +				       x86_xsave_layout &layout)
> +{
> +  return i386_linux_core_read_xsave_info (core_bfd, layout) != 0;
> +}
> +
> +/* See i386-linux-tdep.h.  */
> +
>    const struct target_desc *
>    i386_linux_read_description (uint64_t xcr0)
>    {
> @@ -708,7 +711,8 @@ i386_linux_core_read_description (struct gdbarch *gdbarch,
>    				  bfd *abfd)
>    {
>      /* Linux/i386.  */
> -  uint64_t xcr0 = i386_linux_core_read_xcr0 (abfd);
> +  x86_xsave_layout layout;
> +  uint64_t xcr0 = i386_linux_core_read_xsave_info (abfd, layout);
>      const struct target_desc *tdesc = i386_linux_read_description (xcr0);
>    
>      if (tdesc != NULL)
> @@ -767,9 +771,9 @@ i386_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>    
>      cb (".reg", 68, 68, &i386_gregset, NULL, cb_data);
>    
> -  if (tdep->xcr0 & X86_XSTATE_AVX)
> -    cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0),
> -	X86_XSTATE_SIZE (tdep->xcr0), &i386_linux_xstateregset,
> +  if (tdep->xsave_layout.sizeof_xsave != 0)
> +    cb (".reg-xstate", tdep->xsave_layout.sizeof_xsave,
> +	tdep->xsave_layout.sizeof_xsave, &i386_linux_xstateregset,
>    	"XSAVE extended state", cb_data);
>      else if (tdep->xcr0 & X86_XSTATE_SSE)
>        cb (".reg-xfp", 512, 512, &i386_fpregset, "extended floating-point",
> @@ -872,6 +876,8 @@ i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>      tdep->sc_num_regs = ARRAY_SIZE (i386_linux_sc_reg_offset);
>    
>      tdep->xsave_xcr0_offset = I386_LINUX_XSAVE_XCR0_OFFSET;
> +  set_gdbarch_core_read_x86_xsave_layout
> +    (gdbarch, i386_linux_core_read_x86_xsave_layout);
>    
>      set_gdbarch_process_record (gdbarch, i386_process_record);
>      set_gdbarch_process_record_signal (gdbarch, i386_linux_record_signal);
> diff --git a/gdb/i386-linux-tdep.h b/gdb/i386-linux-tdep.h
> index c0fd1f7f300..bd8e328b7fe 100644
> --- a/gdb/i386-linux-tdep.h
> +++ b/gdb/i386-linux-tdep.h
> @@ -20,6 +20,8 @@
>    #ifndef I386_LINUX_TDEP_H
>    #define I386_LINUX_TDEP_H
>    
> +#include "gdbsupport/x86-xstate.h"
> +
>    /* The Linux kernel pretends there is an additional "orig_eax"
>       register.  Since GDB needs access to that register to be able to
>       properly restart system calls when necessary (see
> @@ -34,8 +36,18 @@
>    /* Total number of registers for GNU/Linux.  */
>    #define I386_LINUX_NUM_REGS (I386_LINUX_ORIG_EAX_REGNUM + 1)
>    
> -/* Get XSAVE extended state xcr0 from core dump.  */
> -extern uint64_t i386_linux_core_read_xcr0 (bfd *abfd);
> +/* Read the XSAVE extended state xcr0 value from the ABFD core file.
> +   If it appears to be valid, return it and fill LAYOUT with values
> +   inferred from that value.
> +
> +   Otherwise, return 0 to indicate no state was found and leave LAYOUT
> +   untouched.  */
> +extern uint64_t i386_linux_core_read_xsave_info (bfd *abfd,
> +						 x86_xsave_layout &layout);
> +
> +/* Implement the core_read_x86_xsave_layout gdbarch method.  */
> +extern bool i386_linux_core_read_x86_xsave_layout (struct gdbarch *gdbarch,
> +						   x86_xsave_layout &layout);
>    
>    /* Handle and display information related to the MPX bound violation
>       to the user.  */
> @@ -52,14 +64,7 @@ extern const struct target_desc *i386_linux_read_description (uint64_t xcr0);
>    	  fxsave_bytes[0..463]
>    	  sw_usable_bytes[464..511]
>    	  xstate_hdr_bytes[512..575]
> -	  avx_bytes[576..831]
> -	  mpx_bytes [960..1032]
> -	  avx512_k_regs[1088..1152]
> -	  avx512_zmmh_regs0-7[1153..1407]
> -	  avx512_zmmh_regs8-15[1408..1663]
> -	  avx512_zmm_regs16-31[1664..2687]
> -	  pkru[2688..2752]
> -	  future_state etc
> +	  extended state regions (AVX, MPX, AVX512, PKRU, etc.)
>    	};
>    
>      Same memory layout will be used for the coredump NT_X86_XSTATE

Ping?

-- 
John Baldwin