Re: [PATCH v5 10/16] [gdb/aarch64] sme: Fixup sigframe gdbarch when vg/svg changes

Luis Machado via Gdb-patches
2023-09-08T11:08:48Z

It would be nice to have a global maintainer go through this one, as it touches a small part of generic gdb code.

On 9/7/23 16:20, Luis Machado via Gdb-patches wrote:
> Updates in v4:
>
> - Addressed review comments
>
> ---
>
> With SME, where you have two different vector lengths (vl and svl), it may be
> the case that the current frame has a set of vector lengths (A) but the signal
> context has a distinct set of vector lengths (B).
>
> In this case, we may run into a situation where GDB attempts to use a gdbarch
> created for set A, but it is really dealing with a frame that was using set
> B.
>
> This is problematic, specially with SME, because now we have a different
> number of pseudo-registers and types that gets cached on creation of each
> gdbarch variation.
>
> For AArch64 we really need to be able to use the correct gdbarch for each
> frame, and I noticed the signal frame (tramp-frame) doesn't have a settable
> prev_arch field. So it ends up using the default frame_unwind_arch function
> and eventually calling get_frame_arch (next_frame). That means the previous
> frame will always have the same gdbarch as the current frame.
>
> This patch first refactors the AArch64/Linux signal context code, simplifying
> it and making it reusable for our purposes of calculating the previous frame's
> gdbarch.
>
> I introduced a struct that holds information that we have found in the signal
> context, and with which we can make various decisions.
>
> Finally, a small change to tramp-frame.c and tramp-frame.h to expose a
> prev_arch hook that the architecture can set.
>
> With this new field, AArch64/Linux can implement a hook that looks at the
> signal context and infers the gdbarch for the previous frame.
>
> Regression-tested on aarch64-linux Ubuntu 22.04/20.04.
> ---
> gdb/aarch64-linux-tdep.c | 278 +++++++++++++++++++++++++++------------
> gdb/tramp-frame.c | 1 +
> gdb/tramp-frame.h | 11 ++
> 3 files changed, 204 insertions(+), 86 deletions(-)
>
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index f76d1888072..39855844ad0 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -184,6 +184,39 @@
> #define AARCH64_SME_CONTEXT_SIZE(svq) \
> (AARCH64_SME_CONTEXT_REGS_OFFSET + AARCH64_SME_CONTEXT_ZA_SIZE (svq))
>
> +/* Holds information about the signal frame. */
> +struct aarch64_linux_sigframe
> +{
> + /* The stack pointer value. */
> + CORE_ADDR sp = 0;
> + /* The sigcontext address. */
> + CORE_ADDR sigcontext_address = 0;
> + /* The start/end signal frame section addresses. */
> + CORE_ADDR section = 0;
> + CORE_ADDR section_end = 0;
> +
> + /* Starting address of the section containing the general purpose
> + registers. */
> + CORE_ADDR gpr_section = 0;
> + /* Starting address of the section containing the FPSIMD registers. */
> + CORE_ADDR fpsimd_section = 0;
> + /* Starting address of the section containing the SVE registers. */
> + CORE_ADDR sve_section = 0;
> + /* Starting address of the section containing the ZA register. */
> + CORE_ADDR za_section = 0;
> + /* Starting address of the section containing extra information. */
> + CORE_ADDR extra_section = 0;
> +
> + /* The vector length (SVE or SSVE). */
> + ULONGEST vl = 0;
> + /* The streaming vector length (SSVE/ZA). */
> + ULONGEST svl = 0;
> + /* True if we are in streaming mode, false otherwise. */
> + bool streaming_mode = false;
> + /* True if we have a ZA payload, false otherwise. */
> + bool za_payload = false;
> +};
> +
> /* Read an aarch64_ctx, returning the magic value, and setting *SIZE to the
> size, or return 0 on error. */
>
> @@ -318,129 +351,115 @@ aarch64_linux_restore_vregs (struct gdbarch *gdbarch,
> }
> }
>
> -/* Implement the "init" method of struct tramp_frame. */
> +/* Given a signal frame THIS_FRAME, read the signal frame information into
> + SIGNAL_FRAME. */
>
> static void
> -aarch64_linux_sigframe_init (const struct tramp_frame *self,
> - frame_info_ptr this_frame,
> - struct trad_frame_cache *this_cache,
> - CORE_ADDR func)
> +aarch64_linux_read_signal_frame_info (frame_info_ptr this_frame,
> + struct aarch64_linux_sigframe &signal_frame)
> {
> - struct gdbarch *gdbarch = get_frame_arch (this_frame);
> - enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
> - aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (gdbarch);
> - CORE_ADDR sp = get_frame_register_unsigned (this_frame, AARCH64_SP_REGNUM);
> - CORE_ADDR sigcontext_addr = (sp + AARCH64_RT_SIGFRAME_UCONTEXT_OFFSET
> - + AARCH64_UCONTEXT_SIGCONTEXT_OFFSET );
> - CORE_ADDR section = sigcontext_addr + AARCH64_SIGCONTEXT_RESERVED_OFFSET;
> - CORE_ADDR section_end = section + AARCH64_SIGCONTEXT_RESERVED_SIZE;
> - CORE_ADDR fpsimd = 0;
> - CORE_ADDR sve_regs = 0;
> - CORE_ADDR za_state = 0;
> - uint64_t svcr = 0;
> + signal_frame.sp = get_frame_register_unsigned (this_frame, AARCH64_SP_REGNUM);
> + signal_frame.sigcontext_address
> + = signal_frame.sp + AARCH64_RT_SIGFRAME_UCONTEXT_OFFSET
> + + AARCH64_UCONTEXT_SIGCONTEXT_OFFSET;
> + signal_frame.section
> + = signal_frame.sigcontext_address + AARCH64_SIGCONTEXT_RESERVED_OFFSET;
> + signal_frame.section_end
> + = signal_frame.section + AARCH64_SIGCONTEXT_RESERVED_SIZE;
> +
> + signal_frame.gpr_section
> + = signal_frame.sigcontext_address + AARCH64_SIGCONTEXT_XO_OFFSET;
> +
> + /* Search for all the other sections, stopping at null. */
> + CORE_ADDR section = signal_frame.section;
> + CORE_ADDR section_end = signal_frame.section_end;
> uint32_t size, magic;
> - size_t vq = 0, svq = 0;
> bool extra_found = false;
> - int num_regs = gdbarch_num_regs (gdbarch);
> -
> - /* Read in the integer registers. */
> + enum bfd_endian byte_order
> + = gdbarch_byte_order (get_frame_arch (this_frame));
>
> - for (int i = 0; i < 31; i++)
> - {
> - trad_frame_set_reg_addr (this_cache,
> - AARCH64_X0_REGNUM + i,
> - sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
> - + i * AARCH64_SIGCONTEXT_REG_SIZE);
> - }
> - trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM,
> - sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
> - + 31 * AARCH64_SIGCONTEXT_REG_SIZE);
> - trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM,
> - sigcontext_addr + AARCH64_SIGCONTEXT_XO_OFFSET
> - + 32 * AARCH64_SIGCONTEXT_REG_SIZE);
> -
> - /* Search for the FP and SVE sections, stopping at null. */
> while ((magic = read_aarch64_ctx (section, byte_order, &size)) != 0
> && size != 0)
> {
> switch (magic)
> {
> case AARCH64_FPSIMD_MAGIC:
> - fpsimd = section;
> - section += size;
> - break;
> + {
> + signal_frame.fpsimd_section = section;
> + section += size;
> + break;
> + }
>
> case AARCH64_SVE_MAGIC:
> {
> /* Check if the section is followed by a full SVE dump, and set
> sve_regs if it is. */
> gdb_byte buf[4];
> - uint16_t flags;
> -
> - if (!tdep->has_sve ())
> - break;
>
> + /* Extract the vector length. */
> if (target_read_memory (section + AARCH64_SVE_CONTEXT_VL_OFFSET,
> buf, 2) != 0)
> {
> + warning (_("Failed to read the vector length from the SVE "
> + "signal frame context."));
> section += size;
> break;
> }
> - vq = sve_vq_from_vl (extract_unsigned_integer (buf, 2, byte_order));
>
> - /* If SME is supported, also read the flags field. It may
> - indicate if this SVE context is for streaming mode (SSVE). */
> - if (tdep->has_sme ())
> + signal_frame.vl = extract_unsigned_integer (buf, 2, byte_order);
> +
> + /* Extract the flags to check if we are in streaming mode. */
> + if (target_read_memory (section
> + + AARCH64_SVE_CONTEXT_FLAGS_OFFSET,
> + buf, 2) != 0)
> {
> - if (target_read_memory (section
> - + AARCH64_SVE_CONTEXT_FLAGS_OFFSET,
> - buf, 2) != 0)
> - {
> - section += size;
> - break;
> - }
> - flags = extract_unsigned_integer (buf, 2, byte_order);
> -
> - /* Is this SSVE data? If so, enable the SM bit in SVCR. */
> - if (flags & SVE_SIG_FLAG_SM)
> - svcr |= SVCR_SM_BIT;
> + warning (_("Failed to read the flags from the SVE signal frame"
> + " context."));
> + section += size;
> + break;
> }
>
> - if (size >= AARCH64_SVE_CONTEXT_SIZE (vq))
> - sve_regs = section + AARCH64_SVE_CONTEXT_REGS_OFFSET;
> + uint16_t flags = extract_unsigned_integer (buf, 2, byte_order);
>
> + /* Is this SSVE data? If so, we are in streaming mode. */
> + signal_frame.streaming_mode
> + = (flags & SVE_SIG_FLAG_SM) ? true : false;
> +
> + ULONGEST vq = sve_vq_from_vl (signal_frame.vl);
> + if (size >= AARCH64_SVE_CONTEXT_SIZE (vq))
> + {
> + signal_frame.sve_section
> + = section + AARCH64_SVE_CONTEXT_REGS_OFFSET;
> + }
> section += size;
> break;
> }
>
> case AARCH64_ZA_MAGIC:
> {
> - if (!tdep->has_sme ())
> - {
> - section += size;
> - break;
> - }
> -
> /* Check if the section is followed by a full ZA dump, and set
> za_state if it is. */
> gdb_byte buf[2];
>
> + /* Extract the streaming vector length. */
> if (target_read_memory (section + AARCH64_SME_CONTEXT_SVL_OFFSET,
> buf, 2) != 0)
> {
> + warning (_("Failed to read the streaming vector length from "
> + "ZA signal frame context."));
> section += size;
> break;
> }
> - svq = sve_vq_from_vl (extract_unsigned_integer (buf, 2,
> - byte_order));
> +
> + signal_frame.svl = extract_unsigned_integer (buf, 2, byte_order);
> + ULONGEST svq = sve_vq_from_vl (signal_frame.svl);
>
> if (size >= AARCH64_SME_CONTEXT_SIZE (svq))
> {
> - za_state = section + AARCH64_SME_CONTEXT_REGS_OFFSET;
> - /* We have ZA data. Enable the ZA bit in SVCR. */
> - svcr |= SVCR_ZA_BIT;
> + signal_frame.za_section
> + = section + AARCH64_SME_CONTEXT_REGS_OFFSET;
> + signal_frame.za_payload = true;
> }
> -
> section += size;
> break;
> }
> @@ -456,11 +475,14 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
> if (target_read_memory (section + AARCH64_EXTRA_DATAP_OFFSET,
> buf, 8) != 0)
> {
> + warning (_("Failed to read the extra section address from the"
> + " signal frame context."));
> section += size;
> break;
> }
>
> section = extract_unsigned_integer (buf, 8, byte_order);
> + signal_frame.extra_section = section;
> extra_found = true;
> break;
> }
> @@ -476,11 +498,48 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
> if (!extra_found && section > section_end)
> break;
> }
> +}
> +
> +/* Implement the "init" method of struct tramp_frame. */
> +
> +static void
> +aarch64_linux_sigframe_init (const struct tramp_frame *self,
> + frame_info_ptr this_frame,
> + struct trad_frame_cache *this_cache,
> + CORE_ADDR func)
> +{
> + /* Read the signal context information. */
> + struct aarch64_linux_sigframe signal_frame;
> + aarch64_linux_read_signal_frame_info (this_frame, signal_frame);
> +
> + /* Now we have all the data required to restore the registers from the
> + signal frame. */
> +
> + /* Restore the general purpose registers. */
> + CORE_ADDR offset = signal_frame.gpr_section;
> + for (int i = 0; i < 31; i++)
> + {
> + trad_frame_set_reg_addr (this_cache, AARCH64_X0_REGNUM + i, offset);
> + offset += AARCH64_SIGCONTEXT_REG_SIZE;
> + }
> + trad_frame_set_reg_addr (this_cache, AARCH64_SP_REGNUM, offset);
> + offset += AARCH64_SIGCONTEXT_REG_SIZE;
> + trad_frame_set_reg_addr (this_cache, AARCH64_PC_REGNUM, offset);
>
> - if (sve_regs != 0)
> + struct gdbarch *gdbarch = get_frame_arch (this_frame);
> + aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (gdbarch);
> +
> + /* Restore the SVE / FPSIMD registers. */
> + if (tdep->has_sve () && signal_frame.sve_section != 0)
> {
> - CORE_ADDR offset;
> + ULONGEST vq = sve_vq_from_vl (signal_frame.vl);
> + CORE_ADDR sve_regs = signal_frame.sve_section;
> +
> + /* Restore VG. */
> + trad_frame_set_reg_value (this_cache, AARCH64_SVE_VG_REGNUM,
> + sve_vg_from_vl (signal_frame.vl));
>
> + int num_regs = gdbarch_num_regs (gdbarch);
> for (int i = 0; i < 32; i++)
> {
> offset = sve_regs + (i * vq * 16);
> @@ -510,30 +569,75 @@ aarch64_linux_sigframe_init (const struct tramp_frame *self,
> trad_frame_set_reg_addr (this_cache, AARCH64_SVE_FFR_REGNUM, offset);
> }
>
> - if (fpsimd != 0)
> + /* Restore the FPSIMD registers. */
> + if (signal_frame.fpsimd_section != 0)
> {
> + CORE_ADDR fpsimd = signal_frame.fpsimd_section;
> +
> trad_frame_set_reg_addr (this_cache, AARCH64_FPSR_REGNUM,
> fpsimd + AARCH64_FPSIMD_FPSR_OFFSET);
> trad_frame_set_reg_addr (this_cache, AARCH64_FPCR_REGNUM,
> fpsimd + AARCH64_FPSIMD_FPCR_OFFSET);
>
> /* If there was no SVE section then set up the V registers. */
> - if (sve_regs == 0)
> + if (!tdep->has_sve () || signal_frame.sve_section == 0)
> aarch64_linux_restore_vregs (gdbarch, this_cache, fpsimd);
> }
>
> - if (za_state != 0)
> + /* Restore the SME registers. */
> + if (tdep->has_sme ())
> {
> - /* Restore the ZA state. */
> - trad_frame_set_reg_addr (this_cache, tdep->sme_za_regnum,
> - za_state);
> + if (signal_frame.za_section != 0)
> + {
> + /* Restore the ZA state. */
> + trad_frame_set_reg_addr (this_cache, tdep->sme_za_regnum,
> + signal_frame.za_section);
> + }
> +
> + /* Restore/Reconstruct SVCR. */
> + ULONGEST svcr = 0;
> + svcr |= signal_frame.za_payload ? SVCR_ZA_BIT : 0;
> + svcr |= signal_frame.streaming_mode ? SVCR_SM_BIT : 0;
> + trad_frame_set_reg_value (this_cache, tdep->sme_svcr_regnum, svcr);
> +
> + /* Restore SVG. */
> + trad_frame_set_reg_value (this_cache, tdep->sme_svg_regnum,
> + sve_vg_from_vl (signal_frame.svl));
> }
>
> - /* If SME is supported, set SVCR as well. */
> - if (tdep->has_sme ())
> - trad_frame_set_reg_value (this_cache, tdep->sme_svcr_regnum, svcr);
> + trad_frame_set_id (this_cache, frame_id_build (signal_frame.sp, func));
> +}
>
> - trad_frame_set_id (this_cache, frame_id_build (sp, func));
> +/* Implements the "prev_arch" method of struct tramp_frame. */
> +
> +static struct gdbarch *
> +aarch64_linux_sigframe_prev_arch (frame_info_ptr this_frame,
> + void **frame_cache)
> +{
> + struct trad_frame_cache *cache
> + = (struct trad_frame_cache *) *frame_cache;
> +
> + gdb_assert (cache != nullptr);
> +
> + struct aarch64_linux_sigframe signal_frame;
> + aarch64_linux_read_signal_frame_info (this_frame, signal_frame);
> +
> + /* The SVE vector length and the SME vector length may change from frame to
> + frame. Make sure we report the correct architecture to the previous
> + frame.
> +
> + We can reuse the next frame's architecture here, as it should be mostly
> + the same, except for potential different vg and svg values. */
> + const struct target_desc *tdesc
> + = gdbarch_target_desc (get_frame_arch (this_frame));
> + aarch64_features features = aarch64_features_from_target_desc (tdesc);
> + features.vq = sve_vq_from_vl (signal_frame.vl);
> + features.svq = (uint8_t) sve_vq_from_vl (signal_frame.svl);
> +
> + struct gdbarch_info info;
> + info.bfd_arch_info = bfd_lookup_arch (bfd_arch_aarch64, bfd_mach_aarch64);
> + info.target_desc = aarch64_read_description (features);
> + return gdbarch_find_by_info (info);
> }
>
> static const struct tramp_frame aarch64_linux_rt_sigframe =
> @@ -550,7 +654,9 @@ static const struct tramp_frame aarch64_linux_rt_sigframe =
> {0xd4000001, ULONGEST_MAX},
> {TRAMP_SENTINEL_INSN, ULONGEST_MAX}
> },
> - aarch64_linux_sigframe_init
> + aarch64_linux_sigframe_init,
> + nullptr, /* validate */
> + aarch64_linux_sigframe_prev_arch, /* prev_arch */
> };
>
> /* Register maps. */
> diff --git a/gdb/tramp-frame.c b/gdb/tramp-frame.c
> index c69ee6efc2c..94e42e9fec1 100644
> --- a/gdb/tramp-frame.c
> +++ b/gdb/tramp-frame.c
> @@ -170,5 +170,6 @@ tramp_frame_prepend_unwinder (struct gdbarch *gdbarch,
> unwinder->stop_reason = default_frame_unwind_stop_reason;
> unwinder->this_id = tramp_frame_this_id;
> unwinder->prev_register = tramp_frame_prev_register;
> + unwinder->prev_arch = tramp_frame->prev_arch;
> frame_unwind_prepend_unwinder (gdbarch, unwinder);
> }
> diff --git a/gdb/tramp-frame.h b/gdb/tramp-frame.h
> index fa0241acb2d..9b43d5e1a36 100644
> --- a/gdb/tramp-frame.h
> +++ b/gdb/tramp-frame.h
> @@ -42,6 +42,13 @@ struct trad_frame_cache;
> instruction sequence. */
> #define TRAMP_SENTINEL_INSN ULONGEST_MAX
>
> +/* Assuming the frame chain: (outer) prev <-> this <-> next (inner);
> + use THIS frame, and implicitly the NEXT frame's register unwind
> + method, to return PREV frame's architecture. */
> +
> +typedef struct gdbarch *(frame_prev_arch_ftype) (frame_info_ptr this_frame,
> + void **this_prologue_cache);
> +
> struct tramp_frame
> {
> /* The trampoline's type, some a signal trampolines, some are normal
> @@ -75,6 +82,10 @@ struct tramp_frame
> int (*validate) (const struct tramp_frame *self,
> frame_info_ptr this_frame,
> CORE_ADDR *pc);
> +
> + /* Given the current frame in THIS_FRAME and a frame cache in FRAME_CACHE,
> + return the architecture of the previous frame. */
> + frame_prev_arch_ftype *prev_arch;
> };
>
> void tramp_frame_prepend_unwinder (struct gdbarch *gdbarch,