[PATCH v3 10/16] [gdb/aarch64] sme: Fixup sigframe gdbarch when vg/svg changes

Luis Machado via Gdb-patches
2023-06-30T13:49:00Z

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 | 279 +++++++++++++++++++++++++++------------
gdb/tramp-frame.c | 1 +
gdb/tramp-frame.h | 12 ++
3 files changed, 206 insertions(+), 86 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 1e12a8f0279..c973a790f62 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. */

@@ -319,129 +352,115 @@ 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_SVE_CONTEXT_VL_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;
}
@@ -457,11 +476,14 @@ 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;
}
@@ -477,11 +499,49 @@ 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.sigcontext_address + AARCH64_SIGCONTEXT_XO_OFFSET;
+ 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);
@@ -511,30 +571,75 @@ 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 =
@@ -551,7 +656,9 @@ 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..563c34ae595 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, 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 +82,11 @@ 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. */
+ struct gdbarch *(*prev_arch) (frame_info_ptr this_frame,
+ void **frame_cache);
};

void tramp_frame_prepend_unwinder (struct gdbarch *gdbarch,
--
2.25.1